EXTENDED LEARNING INSTITUTE
NORTHERN VIRGINIA COMMUNITY COLLEGE
LABORATORY GUIDE
CHM 111
College Chemistry I
ELI HOTLINE: (703) 323-3347
V/TDD: (703) 323-3717
Version 1/02
CHM 111
Copyright © 2002 by Northern Virginia Community College. All rights reserved.
CHM 111 Laboratory Guide
Table of Contents
Overview of CHM 111 Laboratory Component ........................................................... 1
On-Campus Laboratory Experiments ............................................................... 1
Off-Campus Laboratory Exercises .................................................................... 2
Policies and Procedures for On-Campus Laboratories ............................................. 3
Prelaboratory for Dry Lab 3 -- Chemical Models: Lewis Structures ......................... 5
Instructions for Off-Campus Laboratory Exercises ................................................. 14
Inorganic Nomenclature .................................................................................. 15
Scientific Literature .......................................................................................... 32
Exercise 1: Library Information Retrieval ............................................ 33
Exercise 2: Research Report ................................................................ 34
Smithsonian Lab Exercises ............................................................................. 35
Exercise 1: Hands-on Science Center ................................................. 36
Exercise 2: “Science in American Life” Exhibit .................................. 37
Chromatography of Food Dyes ....................................................................... 38
Overview of CHM 111 Laboratory Component
The laboratory component of the ELI course CHM 111, College Chemistry I, consists of ten
laboratory exercises: four on-campus laboratory experiments, one Lab Safety, Orientation,
and Techniques, one Nomenclature Lab and Test, three CyberChem CD-ROM CyberLabs,
and your choice of one out of five off-campus experiments.
On-Campus Laboratory Experiments (all are mandatory)
Scheduling
Four experiments are scheduled in the chemistry lab on Annandale Campus on Saturdays from
9:00 am to 3:30 pm during the semester. These are to be done in groups of four students. These
experiments have been selected from the Laboratory Manual for Principles of General Chemistry,
6th Edition. These are:
1.
2.
3.
4.
Experiment 2: Identification of a Compound: Physical Properties -- read the
textbook assignments for Units 1 and 2
Experiment 9: A Volumetric Analysis -- read the textbook assignments for Units 3 & 4
Experiment 12: Inorganic Compounds and Metathesis Reactions -- read the textbook
assignments for Units 3 and 4
Dry Lab 3: Atomic and Molecular Structure -- read the textbook assignments for
Units 7, 8, and 9; also complete the Prelaboratory assignment (Chemical Models: Lewis
Structures) on pages 5 - 12 of this Lab Guide.
Complete the Prelaboratory Assignment questions in the Laboratory Manual for each
scheduled experiment individually, not in groups. Submit it to the instructor in Lab. Perform
each experiment and submit a Lab Report as per the described format. Allow three hours to
complete one experiment. You must plan to do two experiments on each Saturday, 9-12 and
12:30-3:30
Preparation for first on-campus laboratory experiment
Before reporting to the Annandale Campus chemistry lab for the first time, you should:
a.
complete Assignment 0 (see your online Course Guide) including your Course
Completion Plan on the online forum.
b.
Do the Lab Safety, Orientation, and Techniques off-campus lab (see instructions in the
Off-Campus Laboratory Exercises section on the next page).
c.
read the Procedures and Policies for On-Campus Laboratories section of this Guide.
1
d.
view the Lab Safety Video in one of the campus libraries and take the Lab Safety quiz
(available at any NVCC campus Testing Center). Note: you must pass this safety quiz
and present a form certifying this to the lab instructor in order to be admitted to the lab.
Off-campus Laboratory Exercises
Mandatory Exercises:
5.
6.
7.
8.
9.
Lab Safety, Orientation, and Techniques -- Read Laboratory Safety and Guidelines,
Laboratory Data, and Laboratory Techniques sections; Read Dry Lab 1, complete
Sections A through D and submit pages 35-36 and pages 41-42 stapled together
Inorganic Nomenclature Lab and Nomenclature Test
CyberLab 3: Combustion Analysis -- read textbook assignments for Unit 3
CyberLab 4: Precipitation Reactions -- read textbook assignments for Units 3 & 4
CyberLab 6: Hess’ Law -- read textbook assignments for Unit 6
Complete instructions for Lab 6 is found in the Instructions for Off-Campus Laboratory
Exercises section of this Laboratory Guide.
Complete instructions for the three CyberLabs (CyberLabs 3, 4, and 6) are found on the CyberChem CD-ROM. For the CyberLabs, after performing each experiment submit a Lab Report
using the format described in the Procedures and Policies for On-Campus Laboratories section of
this Laboratory Guide.
Optional Exercises:
10a.
10b.
10c.
10d.
10e.
Choose one of the following five experiments:
Scientific Literature: Library Information Retrieval
Scientific Literature: Research Report
Smithsonian Institution: Visit to “Science in American Life” exhibit
Smithsonian Institution: Visit to “Hands-on Science Center”
Chromatography of M&M Candies
Complete instructions for these optional labs are found in the Instructions for Off-Campus
Laboratory Exercises section of this Laboratory Guide.
2
Procedures and Policies for On-Campus Laboratories
During the lab
-
Identify one member of your laboratory group to be the designated leader for the
experiment. This person will take the official set of data and observations during the lab
and coordinate the preparation of the lab report.
Each member of the group should record notes, observations and data on the Data Sheet
provided in the laboratory module. These data and observations are to be written in ink.
Follow all general laboratory safety rules and specific safety precautions and disposal
procedures for the experiment.
Have the instructor initial the official copies of all data and observations that will be
turned as part of the lab report.
-
NOTE: It is important that you follow the rule that all observations and data be recorded in
ink. These constitute an official and unchangeable record of the experiment. If there is
disagreement within the group concerning a measurement or observation, it must be repeated.
If the second determination differs from the original one, the original is crossed out with a
single line also in ink and the new value entered. A notation is added explaining why
repetition was necessary. It is essential that all observers agree on observation before it is
recorded, and that each member of a group assume responsibility for assuring that everyone
records the same data. If it is impossible to agree on an observation or measurement, even
after repeating it, the details of the argument are to be included as part of the observation so
they become part of the record.
Following the lab
Complete and submit a lab report within 2 weeks after performing the experiment. One lab
report will be submitted by each group. The content of the report should include the following:
Cover page: Includes lab section, the names of the group members who performed the
experiment and contributed to the writing of the report; number and name of the experiment,
date performed, and date due.
Body of report -- This part of the report will contain:



An introduction stating the purpose of the lab exercise and a brief description of
procedures followed.
The "official" Data Sheet from the lab module exactly as completed during the
experiment.
A page or pages showing all calculations hand written in pencil. Calculations of
3



experimental error are to be included if appropriate for the experiment. Units should be
included for all calculations and the rules for significant figures followed.
A discussion of experimental results including:
- an analysis of results comparing actual results with expected results, i.e.
experimental accuracy;
- a discussion of experimental error (random and systematic) and its possible
sources as well as the precision of results.
A concluding statement summarizing how the experimental results relate to the objective
of the experiment.
A statement from each individual group member describing his/her contribution to the
report.
If the lab experiment includes Post Laboratory Questions, these are to be completed by the group
working together and one copy attached to the lab report.
4
Prelaboratory Assignment for Dry Lab 3
Chemical Models: Lewis Structures
The Problem to be Investigated:



Write Lewis structures for atoms, molecules, and ions.
Predict the empirical formulas of compounds and write their Lewis structures.
Write chemical equations using Lewis structures for the reactants and products.
Background Information
To understand better the nature of matter, chemists become involved in model building. The
structure of a substance can often be pictured in the mind by constructing a physical model to
represent it. By studying the model, predictions can often be made as to the possible physical
and chemical behavior of the substance, and insight is often gained as to its shape and size.
The atoms of a substance are held together by bonds. The nature of the bonding can be
considered also by building a model of the substance. One type of model that is often used is the
Lewis structure. This model shows the sequence of the atoms in the molecule and the
distribution of the outer electrons of the atoms.
In a Lewis structure, the chemical symbol of an element represents the nucleus and all the inner
electrons of an atom of that element. This portion of the structure is sometimes called the atomic
kernel. The outer electrons may be represented by dots added to the kernel.
The number of outer electrons of an element may be determined from its position in the periodic
table. The Roman numeral heading each group or column on the table indicates the number of
outer electrons of each element in that group.
When writing the Lewis structure for lithium, for example, the presence of Li in Group I of the
periodic table indicates Li has one outer electron. The Lewis structure for lithium is:
The Lewis structure for the fluorine atom, F, may be written by recognizing that fluorine is in
Group VII of the periodic table. Thus, fluorine has seven outer electrons. The Lewis structure
for the fluorine atom is:
5
As many of the electrons are written as pairs as is possible. There are three pairs of electrons and
one lone electron for the fluorine atom.
To write the Lewis structure for the fluorine ion, F-note that the negative sign on the fluorine
indicates the ion has one more electron than the fluorine atom. By adding an electron to the
fluorine atom, the Lewis structure of the fluoride ion becomes:
This structure has eight electrons, which are written as four pairs around the fluoride ion. The
ion has a negative one charge.
The Lewis structure for the lithium ion is:
In this case a lithium atom loses an electron and becomes the lithium ion. No outer electrons are
shown and the lithium has a positive one charge.
When writing the Lewis structure for a molecule or a polyatomic ion, the bonding between the
atoms is shown. Two electrons may form a single bond between two atoms.
In the case of the hydrogen molecule, H2, each hydrogen atom has one outer electron. With two
outer electrons available from two hydrogen atoms, an electron-pair bond can be formed between
the two hydrogen atoms. The Lewis structure for H2 is:
A further shorthand allows the electron pair to be represented by a line or a dash between the two
bonding atoms.
For elements in the second and third periods of the periodic table, there is a tendency for the
atoms of the elements to each accommodate eight outer electrons. The resulting outer electron
configuration is like that of a rare gas. Because the eight outer electrons form an octet, the
resulting structure is said to obey the octet rule.
In the case of hydrogen and helium, a filled outer level would contain two electrons. When a
hydrogen atom has two electrons, the structure is said to comply with the duet rule.
How does one begin to write the Lewis structure for the fluorine molecule, F2? There are two
atomic kernels and 14 outer electrons. First, the two atomic kernels are written. Because a two-
6
atom molecule is of necessity linear, the two atomic kernels can be placed as shown in Figure
1(a). Second, a pair of electrons is placed between the two fluorines to form a bond. Finally, the
remaining 12 electrons are distributed, assigning three electron pairs to each fluorine. In Figure
1(c), each fluorine has an octet of electrons.
Chemical equations can be written for some reactions using Lewis structures for both the
reactants and the products. The chemical equation for the reaction of lithium atoms and fluorine
molecules may be written as shown in Equation (1).
The lithium atom has lost an electron to a fluorine atom and become a lithium ion. The fluorine
gains an electron from the lithium atom and becomes a fluoride ion. The product is lithium
fluoride, an ionic compound. Neither the lithium ion nor the fluoride ion share any outer
electrons. The fluoride ion meets the octet rule, while the lithium ion follows the duet rule.
Lewis structures can also be used to predict the empirical formula of a substance formed from
two elements. If silicon and hydrogen reacted to form a compound, what might the Lewis
structure and the empirical formula of the compound be? Silicon is found in Group IV of the
periodic table, which suggests that silicon has four outer electrons. Because hydrogen is in
Group 1, it has one outer electron. Consideration of the Lewis structures for silicon and
a) the atomic kernels
b) the electron-pair bond
c) the distribution of
remaining electrons
Figure 1. The Lewis structure of the fluorine molecule.
for hydrogen suggests that silicon could form four bonds, one with each of four hydrogen atoms.
The resulting structure would have an octet of electrons on the silicon and an empirical formula
of SiH4.
In this experiment, Lewis structures will be used as models for atoms, molecules, and ions. By
considering Lewis models of substances, predictions will be made as to the possible products that
might form from a chemical reaction. Chemical equations will be written in which Lewis
structures will be used as models for reactants and products. By considering the Lewis structures
7
of certain elements in the periodic table, the empirical formula of the product and the Lewis
structure of the product formed will be predicted.
PROCEDURE
In each of the following questions, supply the requested information. A periodic table would be
useful in doing this exercise.
A. Writing Lewis Structures
1. Fill in the remaining spaces with the Lewis structures of each of the second period elements in
the following table.
2. Write a Lewis structure for each of the following:
Ca2+____
Ne____
Cl -____
Na+____
O2-____
3. Example: Lewis structure for hydrogen fluoride, HF.
(a) The total number of outer electrons available is __________.
(b) Write the atomic kernels in the box below.
(c) Write the electron pair to represent the bond between the two kernels.
(d) Distribute the remaining outer electrons between the two atomic kernels.
Lewis Structure of HF
(e) Why is the Lewis structure of HF different from that of LiF?
4. Example: Lewis structure for the water molecule, H2O.
8
(a)
The total number of outer electrons available is _______.
(b)
Write the atomic kernels in the box below. Arrange the kernels so that bonds can be
written between each hydrogen and the oxygen kernel.
(c)
Place an electron-pair bond between each hydrogen and the oxygen kernel.
(d)
Distribute the remaining outer electrons so that the octet rule is followed by oxygen and
the duet rule by hydrogen.
Lewis Structure of H2O
5. Example: Lewis structure for the methane molecule, CH4.
(a)
The total number of outer electrons available is _________.
(b)
Select the atomic kernel of the element which would seem likely to be the central atom in
the molecule. Position the remaining atomic kernels around it in the box below.
(c)
Place an electron pair between each of the two bonding atoms.
(d)
Distribute the remaining outer electrons so that the octet rule is followed by carbon and
the duet rule by hydrogen.
Lewis Structure of CH4
6. Example: Lewis structure for oxygen difluoride, OF2.
(a)
The total number of outer electrons available is ________.
(b)
Arrange the atomic kernels in the box below so that they are positioned according to the
bonds to be formed. Generally, the element appearing nearer the middle of the periodic
table is the central atom.
(c)
Place an electron-pair bond between each fluorine and oxygen kernel.
(d)
Distribute the remaining outer electrons so that oxygen and both fluorines follow the octet
rule.
9
Lewis Structure of OF2
7. Example: Lewis structure for ethylene, C2H4.
(a)
The total number of outer electrons available is _______.
(b)
Hydrocarbons are substances in which carbon atoms are bonded together and which
contain hydrogen atoms attached to the carbon atoms. Arrange the atomic kernels in the
box below.
(c)
Place one electron-pair bond between the atomic kernels.
(d)
Assign the remaining outer electrons to the carbon atomic kernels so that they each have
an octet of electrons.
(e)
If there are not enough outer electrons remaining for the carbon atoms, consider the
possibility of having a multiple bond between two bonding atoms. If there should be two
electron pair bonds between the two carbons, does each carbon comply with the rule of
the octet? Place the remaining pair of electrons in the structure.
Lewis Structure of C2H4
8. Example: Lewis structure for chloroform, CHCl3.
(a)
The total number of outer electrons available is _______.
(b)
Use carbon as the central atomic kernel and place the other kernels accordingly, joining
the kernels with an electron pair to form the necessary bonds. Distribute the remaining
electrons so that carbon and chlorine follow the octet rule.
Lewis Structure of CHCl3
9.
Example: Lewis structure for carbon (IV) oxide, or carbon dioxide, CO2.
(a)
The total number of outer electrons available is ________.
10
(b)
Arrange the atomic kernels in appropriate order. Place electron pairs so that the atoms
are bonded to each other. Distribute the remaining electrons so that the carbon and the
oxygens each have an octet of electrons.
(c)
If there seem to be too few electrons for the structure, consider the possibility of placing a
double bond in the structure. Are two double bonds required?
Lewis Structure of CO 2
10. Example: Lewis structure for the sulfate ion, SO42-, in which the central atom is sulfur.
(a)
The total number of outer electrons available is ________.
Lewis Structure of SO 4 211.
Example: Lewis structure for acetylene, C2H2 , in which the two carbons are bonded
together.
(a)
The total number of outer electrons available is ________.
Lewis Structure of C2H2
B. Prediction of Compounds and of Products of Reactions
1.(a) The hydride of sulfur has an empirical formula of H2S and the central atom is sulfur. The
empirical formula for the hydride of selenium would be expected to be ____ and its Lewis
11
structure would be:
(b)
The hydride of silicon has the empirical formula of SiH4 and silicon is the central atom.
The empirical formula of the hydride of germanium would be expected to be ______ and
its Lewis structure would be:
LEWIS FORMULAS
Write Lewis formulas for the following:
Elemental molecules
Br2
N2
O3
I2
Covalent compounds
H2S
PH3
C2H6
H2SO4
12
Ionic Compounds
CsF
KNO3
(NH4)2SO4
13
Instructions for Off-Campus Laboratory Exercises
for CHM 111-ELI
This section contains instructions for those CHM 111 ELI off-campus laboratory exercises which
are not CyberChem Labs as follows:
Mandatory Exercises:
Lab Safety, Orientation, and Techniques -- Read Laboratory Safety and Guidelines,
Laboratory Data, and Laboratory Techniques sections; Read Dry Lab 1, complete
Sections A through D and submit pages 35-36 and pages 41-42 stapled together
Inorganic Nomenclature -- see page 15
Optional Exercises (choose one):
Scientific Literature Exercise 1: Library Information Retrieval
Scientific Literature Exercise 2: Research Report
Smithsonian Lab Exercise 1: Hands-on Science Center
Smithsonian Lab Exercise 2: “Science in American Life” Exhibit
Chromatography of Food Dyes
14
Inorganic Nomenclature
An Exercise in
Naming Chemical Compounds
and
Writing Chemical Formulas
This exercise should be completed as early as possible. Related material is covered in Chapter 1
and in the Appendix of the text. View the lab video "Nomenclature" available at each of the five
campus libraries. Also read Dry Lab 2B, Inorganic Nomenclature II, and Dry Lab 2C, Inorganic
Nomenclature III.
Note: you must study the Stock system of nomenclature: see page 128. You are not responsible
for knowing the archaic or old system.
Your grade for this exercise will consist of the score earned on the Nomenclature Test you take
in the Testing Lab upon completion of the lab. Exercises contained in the lab need not be turned
in. However, you should complete them all. Be sure to check your responses against the
answers given at the end of the lab write-up.
In the Nomenclature Test you will be asked to identify compounds as ionic or covalent from their
names or formulas, to classify compounds as binary or ternary, to write formulas of compounds
given their names and to write names of compounds given their formulas. This last task is the
most difficult one of those listed. It would be well worth it to put extra effort into developing
this skill.
Any of the compounds or ions discussed in the lab handout may be included on the test.
15
INORGANIC NOMENCLATURE
1.
Introduction
Chemistry is divided into two main branches: organic chemistry and inorganic chemistry.
Organic chemistry is the study of carbon compounds, although some of these are included in the
study of inorganic chemistry. Among these compounds are carbon dioxide and its derivatives,
the carbonates, cyanides, carbon monoxide, and carbon disulfide.
Organic chemists deal with compounds which are relatively large. The properties of these
compounds depend on the spatial arrangement of the atoms within the molecules. Therefore, the
system of nomenclature used for organic chemistry must be detailed and complex.
Inorganic compounds, on the other hand, are commonly named by simply specifying the
proportions of the elements that make up the compound. The two branches of chemistry have
distinctly different but compatible systems of nomenclature, but the objective of both systems is
to name each compound in such a way that the chemical identity of the specific compound is
known with certainty.
2.
The IUPAC System of Inorganic Nomenclature
The evolution of the science of chemistry is traced back to the early fifteen hundreds to the work
of the alchemists and the iatrochemists. Substances often were given names based on their
appearance or source. For example, "blue vitriol" and "bluestone" were two of the names given
to the substance now called copper(II) sulfate. Ammonium hydroxide, the name for household
ammonia, was called "spirits of hartshorn" because it was prepared primarily from the dry
distillation of antlers from the hart, a common European deer.
The alchemists concentrated their efforts on the search for the "philosopher's stone" which they
believed would change common, corrodible base metals into the noble metal, gold. The
iatrochemists studied both plants and minerals, and were searching for the "elixir of life" which
would, they thought, prolong life indefinitely. These early "chemists" worked quite
independently of each other, and were often very secretive about their results. As a result, the
compounds they worked with were described by individually developed symbols, or codes.
There were almost as many symbols for the elements known at that time as there were people
working with them.
As chemistry gradually became more sophisticated and its practitioners began to cooperate and
share results of experiments, the need for a commonly agreed upon set of symbols for the
elements and for a systematic method for naming compounds became urgent. Even so, it was not
until the late eighteenth century that the first widely used system of chemical nomenclature was
developed. This system was developed in France by four prominent scientists, Antoine
Lavoisier, Guyton de Morveau, Comte de Antoine Fourcroy and Comte Claude Berthollet, and
16
published in 1787. Their proposed system emphasized the necessity for a commonly agreed
upon system of naming compounds.
Twenty six years later, in 1813, J. J. Berzelius of Sweden, proposed the use of the first letter of
the Latin name of the element as its symbol. To avoid duplication, he used the second letter from
the name where necessary. Thus carbon was given the symbol C; chlorine, Cl; chromium, Cr.
Berzelius also introduced the idea of writing formulas to indicate the ratio of the elements in the
compound. At first, he wrote the formula for the compound we now call carbon dioxide as
COO; later he changed this to CO2. This system for formulas was not widely accepted until a
journal editor, Justus von Liebig altered the superscripts to subscripts to avoid the comparison
with mathematical symbolism. Finally, carbon dioxide became CO2, and this system was
gradually adopted as standard.
In 1894, the International Congress of Chemists met in Brussels. This Congress was
composed of leading chemists from the major western countries, and an agreement was reached
on a standard system of nomenclature based on that of Lavoisier, et al, and on the system of
formulas patterned after that of Berzelius and Liebig.
In June of 1920, the International Union of Pure and Applied Chemistry was formed with the
aim of this organization being the assurance of international agreement in nomenclature,
chemical symbols, formulas, and other aspects of chemistry where communication among
scientists requires complete uniformity. The IUPAC holds meetings for this purpose every two
years, rotating the site among member nations. The system of nomenclature and formula writing
used here is based on the IUPAC rules and recommendations as presently stated.
A.
Nomenclature of Cations
Cations are formed when an atom loses one or more electrons. These ions will have a
positive electrical charge, and are normally formed from the atoms of metals.
A cation, if present, is always listed first in both names and formulas of compounds. These ions
have the same name as the elements from which they are derived, without any alteration. When
writing the symbol of a cation, the number of electrons lost in its formation is indicated by a
superscript Arabic numeral followed by a positive sign. (For those ions formed by losing one
electron, thus with a charge of positive one, the numeral 1 is commonly omitted.)
Examples:
Na+
Ca2+
17
"en ay positive"
"cee ay two positive"
Some elements, particularly those in the "d" block of the periodic table (transition elements) form
more than one cation. This is because the atom may, under different circumstances, lose a
different number of electrons. To name the cations of such an element, a system known as Stock
notation is preferred. A Roman numeral, representing the number of electrons lost and thus the
positive charge on the ion, is placed in parentheses immediately following the name of the
element.
Examples:
Note:
Fe2+
Fe3+
Cu1+
Cu2+
Hg22+
Hg2+
iron(II)
iron(III)
copper(I)
copper(II)
mercury(I)
mercury(II)
"iron two"
"iron three"
The mercury(I) cation consists of two mercury atoms covalently
bonded together. Each of these atoms has lost one electron so that
the charge on the pair of 1+ ions is 2+.
In the IUPAC system, it is considered inappropriate to use a Roman numeral in naming the ion of
a metal that forms only one cation. It is incorrect to omit the Roman numeral in the name of the
ion of a metal that has more than one possible cation. Therefore, to correctly apply the rules of
this system, it is necessary to know which metals fall into each category. The following
relatively common metallic elements should not have a Roman numeral included as part of their
names in as much as they have only one possible charge on their cations:
(Memorize)
The alkali metals and silver (all form 1+ cations)
The alkaline earths, zinc and cadmium (all form 2+ cations)
Aluminum and scandium (form 3+ cations)
For all other metals, the use of Roman numerals is required.
The NH4+ cation, the ammonium ion, is a common inorganic cation. It is derived from
the compound NH3, ammonia, by the addition of a hydrogen ion to the NH3 molecule. Because
the chemistry of the NH4+ ion somewhat resembles that of metal ions having a 1+ charge, it is
given a name with the "ium" ending common to the Group 1 metals.
B.
Nomenclature of Simple Anions
The nomenclature of all anions depends on alterations of the ending of the name of the
main element to indicate the exact nature of the anion. The simple anions are, for the most part,
single atoms of the nonmetals which have gained one or more electrons. The ending which
indicates the single atom nature of an anion is -ide. The elements which form this type of anion,
the symbol and charge for the anion formed, and its name are given in the following table.
Table 1 - The Single Atom Anions
18
Element
Symbol for Anion
fluorine
chlorine
bromine
iodine
oxygen
sulfur
selenium
tellurium
nitrogen
phosphorus
hydrogen
Name of Anion
FClBrIO2S2Se2Te2N3P3H-
fluoride
chloride
bromide
iodide
oxide
sulfide
selenide
telluride
nitride
phosphide
hydride
Other anions with names ending in ide:
CNOHO22C22-
cyanide (a carbon and nitrogen atom covalently bonded, one electron added
to the pair of atoms.)
hydroxide (a hydrogen and an oxygen atom covalently bonded, one electron added
to the pair of atoms.)
peroxide (two oxygen atoms covalently bonded, two electrons added to the
bonded pair.)
carbide (two carbon atoms covalently bonded, two electrons added to the bonded
pair.)
The names and charges for these ions must be memorized. However, the charges on the
single atom anions can be deduced from position in the periodic table.
The name of a binary compound formed from one or more cations and one or more single atom
anions or cyanide, hydroxide, peroxide or carbide anions is simply the name of the cation
followed by the name of the anion, separated by one space.
Table 2 - Some Compounds Formed from Metals with Only One Ion Charge
Name
sodium chloride
barium chloride
Formula
NaCl
BaCl2
Name
strontium hydroxide
aluminum cyanide
Formula
Sr(OH)2
Al(CN)3
Since the above compounds contain metallic ions of only one possible charge, a Roman numeral
indicating the charge is not included as part of its name.
19
However, if the cation is formed from a metal which can form cations with different charges, and
for which the ion charge must be included as part of its name, the charge on the cation in the
particular compound being named must be determined from the formula and the charge on the
anion. Examples are discussed below.
Table 3 - Some Compounds Formed from Metals with More Than One Possible Ion Charge
Name
iron(II) iodidea
iron(III) iodideb
chromium(III) oxidec
a.
b.
c.
Formula
FeI2
FeI3
Cr2O3
The formula, FeI2, must represent a neutral compound, with no net charge. The iodide
ion has a 1- charge. Two iodide ions represent a total of 2- charges. To be electrically
neutral the iron ion must have a charge of 2+. This is the iron(II) cation.
Three iodide ions represent a total negative charge of 3-. For the formula, FeI3, to
represent a neutral compound the iron cation must have a charge of 3+. This is the
iron(III) ion.
The oxide ions represent a total negative charge of 6-. Therefore, two chromium ions
must have a total charge of 6+. This means each chromium ion has a charge of 3+ in the
compound, and is the chromium(III) ion.
Exercise 1: Write the preferred IUPAC name for the compounds below.
a. CaO
f. Na2O2
k. Al2O3
p. AgI
b. KCl
g. CrBr3
l. CrO3
q. NiS
c. Hg2O
h. Au(CN)3
m. CuO
r. Hg3N2
d. ZnF2
i. Sr3P2
n. PbO2
s. Li3N
e. Ba(OH)2
j. CoS
o. Cu(CN)2
t. CaC2
C.
Binary Compounds of Two Non-metals
For naming compounds containing two elements, both of which are nonmetals, the IUPAC
system recommends the use of a series of prefixes to specify exactly how many atoms of each
element there are in a molecule of the compound. These prefixes and their numerical meanings
are:
1 - mono
5 - penta
8 - octa
2 - di
6 - hexa
9 - nona
3 - tri
7 - hepta
10 – deca
4 - tetra
20
Table 4 - Nomenclature of Binary Compounds Using Numerical Prefixes
Name
Name
Formula
Formula
carbon monoxide
sulfur trioxide
tetraphosphorus hexaoxide
CO
SO3
P4O6
carbon dioxide
dinitrogen pentaoxide
dibromine heptachloride
CO2
N2O5
Br2Cl7
Note: When there is only one atom of the first element in the compound, the prefix "mono" is
not used.
The IUPAC rules state that in the preferred system of nomenclature:
a.
b.
c.
Binary compounds of two nonmetals should be named using the system of numerical
prefixes.
Numerical prefixes should not appear in the name of binary compounds of metals with
nonmetals.
The Stock system of using Roman numerals to indicate ion charges is not appropriate for
naming binary compounds of two nonmetals.
Exercise 2: Name the following binary compounds using the
system of numerical prefixes.
a.
b.
c.
d.
SiO2
Cl2O
S2Cl2
SF6
e. CCl4
f. NF3
g. CS2
h. ClF3
i. N2O3
j. XeF6
Exercise 3: Name the following compounds
using the preferred IUPAC nomenclature.
a.
b.
c.
d.
e.
XeF4
CuCl
Mg(CN)2
Au(OH)3
PCl3
f.
g.
h.
i.
j.
Cs3N
CrCl3
CaO2
CuS
SO2
21
k. N2O4
l. Ag2O
m. MnO2
n. PbO2
o. Hg2O
D.
Writing Formulas from Names for Binary Compounds
When the name of a compound ends in ide, it can be assumed to be a binary compound
formed from:
a.
one or more metal (or ammonium) cations and one or more single atom anions (or
one of the exceptions noted before); or,
b.
two nonmetals.
To correctly write a formula for a compound formed from a metal and non-metal given the name
of the compound:
A.
The charges on both the cation and anion must be known.
Cation charge: If the name includes a Roman numeral, this numeral gives the
number of positive charges on the cation. If the name does not include a Roman
numeral, the charge on the cation must be inferred from the position of the
element in the periodic table or have been memorized.
Anion charge: The charge on the anion is never stated in the name of a
compound, and therefore must be inferred from the position of the element in the
periodic table, or have been memorized.
B.
The formula for a compound must be electrically neutral. This means that the total
number of positive (cation) charges must be exactly balanced by the total number of
negative (anion) charges. More than one cation and/or more than one anion may be
necessary to balance these charges. If so, the number of ions needed is indicated by a
subscript written after the symbol for the ion.
22
Table 5 - Examples of Formulas from Names of Binary Metal/Nonmetal Compounds
Name
sodium chloride
Cation
Anion
Na+
Cl-
Formula
NaCl
(one 1+ ion and one 1- ion result in a neutral compound.)
iron(III) bromide
Fe3+
Br-
FeBr3
(one 3+ ion and the three 1- ions result in a neutral compound.)
silver sulfide
Ag+
S2-
Ag2S
O2-
CaO
(two 1+ ions and 2- ion result in a neutral compound.)
calcium oxide
Ca2+
( one 2+ ion and one 2- ion result in a neutral compound.)
aluminum oxide
Al3+
O2-
Al2O3
(two 3+ ions and three 2- ions give a neutral compound.)
gold(III) cyanide
Au3+
CN-
Au(CN)3
(one 3+ ion and three 1- ions give a neutral compound. The cyanide ion is enclosed in
parentheses to indicate that three CN- ions, each consisting of one C and one N, are
needed.)
ammonium sulfide
NH4+
S2-
(NH4)2S
(two 1+ ions are needed to balance the one 2- charge. Note that the ammonium ion is
enclosed in parentheses to indicate that two multi-atom ions are required.)
To write the formula for a binary compound composed of two nonmetals from its name in which
numerical prefixes have been used, simply write the constituent elements in order given using
subscripts to indicate the number of the atoms indicated by the prefix for each.
23
Exercise 4.
Write the formulas for the following binary compounds
a. magnesium iodide
b. chlorine dioxide
c. chromium(III) sulfide
d. silver bromide
e. mercury(II) hydride
f. ammonium sulfide
g. barium hydroxide
h. strontium phosphide
i. carbon tetraiodide
j. iodine heptafluoride
E.
k. gold (III) hydroxide
l. aluminum nitride
m. iron(II) phosphide
n. oxygen difluoride
o. potassium peroxide
p. gold(I) cyanide
q. zinc oxide
r. selenium disulfide
s. uranium(III) oxide
Archaic System of Cation Nomenclature
At the time Lavoisier and his fellow scientists proposed their system of naming compounds, none
of the metallic elements had more than two known charge states. Thus, they recommended that
the two charge states be differentiated by adding the suffix ous to the Latin name for the element
in the lower charge state, and the suffix ic to the Latin name for higher charge state. This system
is not recommended by IUPAC because many elements have been discovered in more than two
charge states, and because this old system is not as explicit as the stock system. However, it as
yet has not completely disappeared from scientific literature or from labels used by chemical
manufacturers.
Table 6- Comparison Of Some Stock System/ Archaic System Cation Names
Stock System
F.
Archaic
Stock System
Archaic
iron(II)
ferrous
gold(I)
aurous
iron(III)
ferric
gold(III)
auric
copper(I)
cuprous
lead(II)
plumbous
copper(II)
cupric
lead(IV)
plumbic
mercury(I)
mercurous
tin(II)
stannous
Nomenclature of Complex Anions
Complex anions are made up of several atoms. One atom will be the central atom; the others
are referred to as ligands. By far the most common ligand is oxygen, and in the common
complex anions, oxygen is the only ligand. These anions are usually identified by their "trivial"
or common names. For example, the SO42- complex anion oxygen is commonly called the
24
sulfate ion. The IUPAC systematic name for this anion is tetraoxosulfate(VI). Since the trivial
names are the ones in almost universal use within the United States, the rules for forming these
names are discussed here.
In the correct formula for a complex anion, the central atom will appear first. Sulfur is the
central atom in the sulfate ion and it is covalently bonded to four oxygen ligands. This group of
five atoms shares two electrons over and above the number of electrons normally belonging to
one sulfur atom and four oxygen atoms. Thus, the ion has a charge of 2-.
The names of the majority of complex anions with oxygen as the only ligand are derived by
altering the name of the central atom. The following rules set out the derivation of the anion
name:
Rule 1:
Rule 2:
Rule 3:
Rule 4:
The most common oxygen-containing anion has the name of the central atom
altered to "ate."
Anions with one fewer oxygen atom than the most common anion have the
name of the central atom altered to "ite."
Anions with two fewer oxygen atoms than the most common anion have the
prefix "hypo" added to the name of the central atom and the ending altered
to "ite."
Anions with one more oxygen atom than the most common anion have the prefix "per" added to the name of the central atom and the ending altered to "ate."
When writing formulas for compounds containing complex anions, as usual the positive cation
charges and the negative anion charges must be balanced so that the compound is neutral. When
more than one complex anion is required in the formula, the entire anion is placed in parentheses.
The number of anions in the formula is indicated by a subscript outside and to the right of the
parentheses.
If there is only one complex anion required in the formula, the anion is not placed in parentheses.
Table 7 - Examples of Formulas with Complex Anions
Compound
Cation
Anion
Formula
Ag+
Ca2+
Al3+
Sn4+
NO3ClO3SO42NO3-
AgNO3
Ca(ClO3)2
Al2(SO4)3
Sn(NO3)4
silver nitrate
calcium chlorate
aluminum sulfate
tin(IV) nitrate
These formulas are read aloud as:
AgNO3 - "ay gee en oh three"
25
Ca(ClO3)2 - "cee ay - cee ell oh three taken twice"
Al2(SO4)3 - "ay ell two - ess oh four taken three times"
Sn(NO3)4 - "ess en - en oh three taken four times."
The formulas and charges of the complex anions ending in "ate" should be memorized. Rules
2-4 above can then be applied to the memorized formulas to derive the other complex anions
formed from the same central atom. For example:
ClO3- = "chlorate ion"
ClO2- has one less oxygen atom than the chorate ion; therefore it is the "chlorite ion."
(Rule 2)
ClO- has two fewer oxygen atoms than the chlorate ion; therefore it is the "hypochlorite
ion." (Rule 3)
ClO4- has one more oxygen atom than the chlorate ion; therefore it is the "perchlorate
ion." (Rule 4)
Note that the charge on all of the complex anions formed from chlorine have
the same ion charge of -1. This, generally, will be the case for all complex
anions formed from the same central atom.
Because sulfur has the same outer electron configuration as oxygen, it can take the place of an
oxygen ligand in a complex anion. The replacement of an oxygen atom by a sulfur atom is
indicated by prefixing the name of the complex anion by "thio."
Examples:
sulfate
sulfite
cyanate
SO42SO32OCN-
thiosulfate
thiosulfite
thiocyanate
S2O32S2O22SCN-
There are many exceptions to the simplified nomenclature rules described here. The following
list of complex ions ending in "ate" are commonly encountered in course and laboratory work. A
few exceptions to the rules for naming complex anions are also noted. These should be
memorized.
26
Table 8 - Common Complex Anions Ending in "ate" and Exceptions to Rules
Name
Formula
Exceptions to Rules
chlorate
ClO3-
bromate
BrO3-
iodate
IO3-
sulfate
SO42-
thiosulfate
S2O32-
selenate
SeO42-
tellurate
TeO42-
nitrate
NO3-
phosphate
PO43-
arsenate
AsO43-
carbonate
CO32-
acetate
C2H3O2- or CH3COO-
oxalate
C2O42-
cyanate
OCN-
thiocyanate
SCN-
chromate
CrO42-
dichromate
Cr2O72-
manganate
MnO42-
persulfate - S2O82-
permanganate - MnO4-
Exercise 5: Name the following compounds containing complex anions.
a. NaClO3
b. Ca(ClO4)2
c. Fe(ClO2)3
d. Al(ClO)3
e. KNO3
f. (NH4)2SO4
g. (NH4)2SO3
h. (NH4)2S2O3
i. CsC2H3O2
j. CuCrO4
k. BaCO3
l. KMnO4
m. ZnCr2O7
n. Pb(BrO3)2
o. Hg2(BrO2)2
p. Na3PO4
q. KNO2
r. Ag2SeO4
s. Na2C2O4
t. Au(OCN)3
u. AuSCN
v. Ni3(AsO4)2
27
Exercise 6: Write formulas for the following
compounds containing complex anions.
a. sodium iodate
b. zinc cyanate
c. ammonium carbonate
d. iron(III) bromate
e. calcium arsenate
f. potassium persulfate
g. nickel(IV) acetate
h. rubidium hyponitrite
i. ammonium nitrate
j. sodium thiosulfate
k. aluminum oxalate
G.
l. copper(II) phosphite
m. cobalt(II) thiocyanate
n. mercury(I) chlorite
o. aluminum perchlorate
p. sodium oxalate
q. calcium manganate
r. potassium dichromate
s. magnesium bromite
t. silver chlorate
u. barium selenate
v. potassium acetate
Nomenclature of Acids
Compounds containing hydrogen which can be ionized to produce hydrogen ions (H+) when
dissolved in water are named as acids when they are dissolved in water.
1.
Binary Acids
HCl, a binary compound which exists by itself as a gas, will dissolve in water and form H+ ions
and Cl- ions. The pure gas will have the name hydrogen chloride; an aqueous (water) solution of
HCl is called hydrochloric acid.
Rule for binary acids: If a hydrogen containing binary compound is dissolved in water and
if the compound produces H+ ions in solution the name for the solution will be formed by
adding the prefix "hydro", changing the ending of the non-hydrogen element to "ic" and
adding "acid" to the name.
Examples:
HF(g)
hydrogen fluoride
HF(aq) hydrofluoric acid
Note: the (g) and (aq) are added to indicate pure gas and
aqueous solution, respectively.
HCN(g)
hydrogen cyanide
HCN(aq)
hydrocyanic acid
If no indication is given as to whether or not the compound is dissolved in water, either name can
be used.
28
Formulas for this type of compound are easily recognized as hydrogen will be written as the first
element. For example, NH3 (ammonia) does not form an acid solution with water and does not
have its component hydrogen written first in its formula.
2.
Acids Containing Complex Anions (Ternary Acids)
Rule 1:
A compound containing hydrogen as the only cation and a complex anion
with its name ending in "ate" will have the "ate" ending changed to "ic"
and "acid" added to its name.
Rule 2:
A compound containing hydrogen as the only cation and a complex anion
with its name ending in "ite" will have the "ite" ending changed to "ous"
and "acid" added to its name.
Examples:
H2SO4 sulfuric acid, or hydrogen sulfate
HNO3 nitric acid, or hydrogen nitrate
H2SO3 sulfurous acid, or hydrogen sulfite
HClO hypochlorous acid, or hydrogen hypochlorite
HClO4 perchloric acid, or hydrogen perchlorate
HC2H3O2 acetic acid, or hydrogen acetate
If (aq) is included to indicate a water solution of the compound, the acid form of the name must
be used. However, since these compounds are not commonly, and in some cases never, available
in the absence of water, the acid name is usually given even when there is no indication of the
compound being in solution.
Exercise 7. Give the name or write the
formula for the following.
a. HI(aq)
b. HNO2(aq)
c. H2Se(aq)
d. H2CrO4(aq)
e. HBrO4(aq)
f. HSCN(aq)
g. HBrO2(aq)
h. hyponitrous acid
i. oxalic acid
j. phosphoric acid
k. hydrobromic acid
l. bromic acid
m. phosphorous acid
n. manganic acid
29
H.
Answers to Exercises
Exercise 1
a.
calcium oxide
b.
potassium chloride
c.
mercury(I) oxide
d.
zinc fluoride
e.
barium hydroxide
f.
sodium peroxide
g.
chromium(III) bromide
h.
gold(III) cyanide
i.
strontium phosphide
j.
cobalt(II) sulfide
k.
l.
m.
n.
o.
p.
q.
r.
s.
t.
aluminum oxide
chromium(VI) oxide
copper(II) oxide
lead(IV) oxide
copper(II) cyanide
silver iodide
nickel(II) sulfide
mercury(II) nitride
lithium nitride
calcium carbide
Exercise 2.
a.
silicon dioxide
b.
dichlorine monoxide
c.
disulfur dichloride
d.
sulfur hexafluoride
e.
carbon tetrachloride
f.
g.
h.
i.
j.
nitrogen trifluoride
carbon disulfide
chlorine trifluoride
dinitrogen trioxide
xenon hexafluoride
i.
j.
k.
l.
m.
n.
o.
copper(II) sulfide
sulfur dioxide
dinitrogen tetraoxide
silver oxide
manganese(IV) oxide
lead(IV) oxide
mercury(I) oxide
Exercise 3.
a.
xenon tetrafluoride
b.
copper(I) chloride
c.
magnesium cyanide
d.
gold(III) hydroxide
e.
phosphorous trichloride
f.
cesium nitride
g.
chromium(III) chloride
h.
calcium peroxide
Exercise 4.
a.
MgI2
b.
ClO2
c.
Cr2S3
d.
AgBr
e.
HgH2
f.
(NH4)2S
g.
h.
i.
j.
k.
l.
m.
Ba(OH)2
Sr3P2
CI4
IF7
Au(OH)3
AlN
Fe3P2
n.
o.
p.
q.
r.
s.
30
OF2
K2O2
AuCN
ZnO
SeS2
U2O3
Exercise 5.
a.
sodium chlorate
b.
calcium perchlorate
c.
iron(III) chlorite
d.
aluminum hypochlorite
e.
potassium nitrate
f.
ammonium sulfate
g.
ammonium sulfite
h.
ammonium thiosulfate
i.
cesium acetate
j.
copper(II) chromate
k.
barium carbonate
Exercise 6.
a.
NaIO3
b.
Zn(OCN)2
c.
(NH4)2CO3
d.
Fe(BrO3)3
e.
Ca3(AsO4)2
f.
K2S2O8
g.
Ni(C2H3O2)4
h.
Rb2(NO)2
i.
j.
k.
l.
m.
o.
Exercise 7.
a.
hydroiodic acid
b.
nitrous acid
c.
hydroselenic acid
d.
chromic acid
e.
perbromic acid
f.
thiocyanic acid
g.
bromous acid
l.
m.
n.
o.
p.
q.
r.
s.
t.
u.
v.
potassium permanganate
zinc dichromate
lead(II) bromate
mercury(I) bromite
sodium phosphate
potassium nitrite
silver selenate
sodium oxalate
gold(III) cyanate
gold(I) thiocyanate
nickel(II) arsenate
NH4NO3
p.
Na2S2O3
q.
Al2(C2O4)3
r.
Cu3(PO3)2
s.
Co(SCN)2
t.
n.
Hg2(ClO2)2
Al(ClO4)3
v.
h.
i.
j.
k.
l.
m.
n.
Na2C2O4
CaMnO4
K2Cr2O7
Mg(BrO2)2
AgClO3
u.
BaSeO4
KC2H3O2
H2(NO)2(aq) or (HNO)2
H2C2O4(aq)
H3PO4(aq)
HBr(aq)
HBrO3(aq)
H3PO3(aq)
H2MnO4(aq)
31
Scientific Literature
Exercise 1:
LIBRARY INFORMATION RETRIEVAL
Exercise 2:
RESEARCH REPORT
Successful completion of this exercise demands that you demonstrate the ability to use both standard
and electronic means of information retrieval. Several NVCC libraries provide self-guided
information packages and staff who are prepared to demonstrate the use of the library facilities.
However, if you have access to other libraries with significant holdings of scientific material and
information retrieval technology, these libraries may be used to complete this exercise.
You may elect to complete Exercise 1 or Exercise 2 for one lab grade.
32
Exercise 1.
LIBRARY INFORMATION RETRIEVAL
Visit one of the Northern Virginia Community College libraries that have a self-directed library
orientation tour. At present the libraries at the Annandale and Alexandria Campuses provide this
service and the other campuses are in the process of developing it. There is a printed booklet in
each library that is to be used in the self-directed orientation as well as an audio taped
presentation at the Annandale Library.
If you have library privileges from the library of another college or university or from a
government or industrial installation with an extensive science collection you may
undertake this assignment with personnel or library orientation materials from that library.
Attach a copy of the materials provided by the library to Part I of this assignment.
Become familiar with the various electronic information retrieval systems that the NVCC
campus libraries, or another library, have developed and installed. There are systems that allow
access to remote Databases via modem and dial-up facilities as well as stand-alone CD-ROM
systems that have periodic updates and renewals. The library catalogues, the newspaper indexes,
magazine and journal indexes and other electronic databases serve as an excellent base for
researching topics in areas ranging from science to current events to recent breakthroughs in
medical or pharmacological areas.
Research and select one topic in science that is of current interest using the electronic retrieval
systems. Use the researching capabilities of the systems to find and select a topic that you can
use to a research report as described in Exercise 2. The topic can be in any area of science that
interests you, not necessarily in Chemistry, though of course you may choose a topic that is
specifically from Chemistry. You are to submit:
a)
a cover sheet in the usual pre-lab report format as described in Appendix C.
b)
a topic in science that you have selected for research.
c)
a list of information sources, in accepted bibliographic format, that you have
referenced during the above selection of the topic. Organize and list the sources
according to the following categories:
i.
Four references to scientific journals; scientific journals are publications
of professional Scientific and Technological societies and organizations,
such as “The Journal of Chemical Education” published by the American
Chemical Society, “JAMA” The Journal of the American Medical
Association.
ii.
Four references to reference books, including encyclopedias.
iii.
Four references to newspapers and news magazines
iv.
Four references to popular science publications such as “Scientific
American”, “Discover”, “Omni,” “Science News”, etc.
33
Exercise 2: SCIENTIFIC RESEARCH REPORT
Research the topic you have selected using the electronic information retrieval systems and paper
searches. Use current and relevant references and present the information in an organized report
format with an introduction, body and a conclusion. Submit the following:
a)
a cover sheet in the usual prelab report format as described in the Lab Guide.
b)
a two - five page, typed or computer printout research report on your topic.
c)
a bibliography with at least three references from the list of sources consulted
during the search for the topic in Assignment 1 above.
34
Smithsonian Institution
National Museum of American History
Exercise 1: Hands-on Science Center
Exercise 2: “Science in American Life” Exhibit
These exercises may be undertaken at any time during your enrollment period. Each exercise
will earn a separate lab grade.
The exhibits you are directed to visit in these exercises are very popular, both with tourists and
for school visits. Evenings during those times of the year when the museum has evening hours
and Saturday mornings have been recommended as good times to plan to visit these exhibits.
Suggestion: Check with the Smithsonian before making the trip to be sure the museum and these
exhibits in particular are open at the time and date you plan to visit.
35
Exercise 1: Hands-on Science
The "Hands-On Science Center" is one part of the Smithsonian Institution's "Science in American Life"
exhibition. This permanent exhibition is on the first floor, west wing of the National Museum of American
History at 14th Street and Constitution Avenue. "Science in American Life" has been made possible by
funding from the American Chemical Society and several other organizations.
The Hands-On Science Center is organized into several areas so that one can do activities on one's own or
with a staff member.
The Lab Bench area has activities in the following areas:
Food Additives
Testing Water
Unraveling Genes
An Oil Spill
Ozone Hole
There are Activity boxes for the following:
Inspector Forensic
Semiconductors and Radios
Magnets
Radioactivity Around You
Measuring Minds
Plastics
And there are interactive setups for:
Water Distillation Still
Lasers
Global Temperature Changes
At present there are four different hands-on activities in the Lab Bench area in the Hands- On Science
Center. They are presented by museum docents who are trained in demonstrating and conducting the
experiments. These experiments may be modified or changed by the museum staff depending on staff
scheduling, group reservations, and/or budget considerations
The current experiments are as follows:
1. Food Additives
2. DNA Separation
3. Water Pollution Testing
4. Properties of Carbon dioxide
Choose two of the four experiments and carry out the procedures with guidance from a museum docent.
The museum may require you to work with a group of other participants.
Examine the other activities and resources available in the center. Submit:
1.
a formal lab report (see general laboratory report format and guidelines in this Lab Guide)
on the "Hands On Science" experiments performed.
2.
a critique of the Hand-on Science center focusing on:
a.
the quality of the exhibits and activities;
b.
its potential for improving the scientific knowledge of the American public.
36
Exercise 2: “Science in American Life” Exhibit
The Exhibition examines the interaction between science and American society from 1876 to
today. Through artifacts, historical photographs, computer interactives, and multimedia
technology, the exhibition brings to life many of the scientific issues, controversies, and
achievements that have shaped modern American culture.
When the exhibit opened in 1995, it was considered controversial in its portrayal of the effects
scientific discoveries, particularly those of American science, had on mankind and society. The
historical accuracy of the exhibit was also questioned.
Tour the entire "Science in American Life" exhibition.
controversy the exhibit raised.
Request information or research the
Submit a typed or computer printout two to four page double-spaced written report:
1.
on the science/society aspects of the exhibition;
2.
evaluating the exhibit in terms of the controversial issues raised.
37
Chromatography of Food Dyes
and
Determination of the Dyes Present
in M & M Candies
If you have elected to do this off-campus experiment, you will need to obtain chromatography
paper or plates from your lab instructor when you come to campus for an on-campus lab. All
other required materials are readily available at a grocery or drug store.
38
Chromatography of Food Dyes and Determination
of the Dyes Present in M & M Candies1
I.
Introduction
In this experiment you will use the technique of paper chromatography to separate mixtures of
food dyes. Presently, the Food and Drug Administration approves only seven dyes for use in food
products. These are FD&C yellows #5 and #6, reds #3 and #40, blues #1 and #2, and green #3
(FD&C dyes are those approved by for use in Foods, Drugs, and Cosmetics). These dyes are all
large organic molecules. The dye yellow #5 (tartrazine) is known to cause allergic reactions in
some people. It is found in many food sources such as banana cream pudding, lime Jell-O, and
black jelly beans. An M & M package lists it as a dye present in the candies, but is it present in
all the candies or only in those of certain colors? How about the food coloring and egg dyes? Do
these contain yellow #5? The answers to these questions are important to a person who is
allergic to yellow #5 since they need to know which candies they can eat and what colored foods
to avoid because they can be expected to contain this food dye.
To attempt to answer these questions, a technique called chromatography can be used. This is a
method of separating and identifying components of a mixture based on differential migration.
The mixtures to be separated are spotted on a sheet of specialized paper or on coated plate.
The paper or coating constitute the stationary phase of the system. This paper/plate is then
placed into a container so that its lower edge is immersed in a solvent. The solvent travels up
the paper by capillary action and constitutes the mobile phase of the chromatography system.
Components of a mixture spotted on the stationary phase will have varying affinities for both the
stationary phase and the mobile phase. Those with greater affinity for the moving phase spend
longer in the moving phase. They move up the paper/plate with the solvent more rapidly than
solutes which prefer the stationary phase. As the solvent wicks up through the stationary phase,
the solutes (dyes) separate because of their different affinities for the water and the paper. This
process is called chromatographic development. During this process, the solute is constantly
redistributed between the stationary and mobile phases. A solute that spends most of the time in
the stationary phase will remain near its original spot. One that spends most of its time in the
mobile phase will move fairly close to the edge of the solvent line (called the solvent front.)
The distance each component in the mixture travels up the stationary phase is characterized by a
retention factor, symbolized Rf:
1
Adapted from: M. Kandel “Chromatography of M & M Candies” J. of Chem. Educ., 1992, 69(12)988.
_
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The distance traveled by the solute is measured from the original spot to the center or highest
concentration of the solute. The distance traveled by the solvent is measured from the original
solute spot to the limit of movement of the solvent on the paper. Rf values may change from day
to day due to temperature differences, changes in humidity, or variations in the paper or solvent.
Their relative values, however, remain very constant.
II.
Safety precautions: The rubbing ethyl alcohol used is toxic if ingested. Otherwise,
there are no special safety precautions for this experiment.
III.
Waste disposal: Solutions can be poured down the drain; other materials can be placed
in a garbage can. The chromatograms should be saved and taped onto a page of the
submitted report.
Materials needed:

1 set food coloring dyes: red, yellow, blue and green liquid dye sets (for example:
McCormick Food Coloring and Egg Dye) are available at most grocery stores.

1 package assorted color M and M candies;


chromatography paper or coated plate: obtain these from the lab instructor at an oncampus lab session if this experiment is among those you have elected to do;
Note: do not touch the chromatograph paper or plate with your fingers. Hold it
only at the edge or upper corner.

toothpicks and a glass pie plate or other suitable flat container for the solvent;

sodium chloride (ordinary table salt) and water.

rubbingethyl alcohol - 70% (available at most drug stores; e.g. CVS)

paper towels, ruler, pencil, tape (plastic)
Procedure:
1.
Prepare about 250 ml of 0.1% by weight aqueous sodium chloride solution. (If you do
not have the tools at home to weight the salt and water required, simply take 1 standard 8
ounce measuring cup of water ( 225 ml) and a pinch of salt (the amount of salt you
can pinch between your thumb and forefinger.) Stir the added salt into the water and add
1/4 C of the rubbing ethyl alcohol.
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2.
Using a pencil, carefully draw a line 1 cm from
the narrow edge of the chromatography paper.
Make 10 marks along this line at least 1 cm
apart. Also mark the distance about 2/3 of the
height of the paper (see graphic at right).
3.
Label each of the spots on the lower line to
indicate one food dye color (b, y, r, g). Place the
paper on one or two paper towels and use a
toothpick to place a spot of the appropriate color
food dye on each labeled mark. Make sure to
use a different toothpick for each color dye.
Allow the spots to dry and apply a second spot
of the same color to each.
4.
Select at least two of the yellow, red, green, blue, brown and orange M&Ms. Apply the
colors as follows:
a.
Dip one end of a toothpick in water and rub along the shell to extract the dye. Do
not break the shell. Use one toothpick per color of shell. Blot the
toothpick on the paper towel if there is excess water.
b.
Quickly and carefully apply the dye on the appropriate mark on the
chromatography paper.
c.
Repeat steps a-b until the color is strong (3-5 times should be enough.) Allow the
dot to dry each time before reapplying. This is a critical step. The dye from the
M & Ms is not as concentrated as that of the food dyes. Repeat application as
necessary to achieve sufficient concentration of the colored compound to be able
to observe the components into which it may separate.
d.
Allow all of the dots to dry before proceeding.
5.
Roll the paper or gently bend the plate into a half cylinder or curved surface that will
stand upright unsupported. Use the tape to maintain the shape, placing it slightly above
the 2/3 distance mark. Do not allow the edges of the paper to touch each other.
6.
Add the aqueous sodium chloride-ethanol solution to the glass pie plate to a depth of
about 0.5 cm. The solution must not go above the 1cm mark on the chromatography
paper or touch the dye spots when the paper is placed in the beaker. Do not allow the
paper to touch the sides of the container.
7.
Stand the circular chromatography paper in the solvent-containing plate. The solvent will
wick up the paper and as it does so the dyes will resolve into their component colors.
7.
When the solvent front reaches the line you have drawn 2/3 of the distance up the paper,
remove the paper from the solvent. Remove the tape and lay the paper flat on a fresh
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paper towel. Immediately mark the position of each dye with the pencil. The solvent front
will continue to move after removal from the beaker, so it is important to mark the dye
positions immediately.
9.
Measure the distance between the solvent front and the line marking the point of
application of the dyes; also, measure the distance traveled by each component of each
dye. Prepare and enter these measurements in a table which includes a column for each of
the dyes used in the chromatogram.
10.
Calculate the Rf values for each of the spots found in the chromatogram and enter these
into your table.
11.
Repeat the procedure (2-10) using a second piece of chromatography paper, the same
food dyes and the same colors of M&Ms. Add the measurements and calculated Rf
values to the table.
Post lab questions:
1.
The food dyes contain propylene glycol in addition to the dyes and water. The candy
shells contain sucrose (sugar), corn syrup, corn starch, and gum acacia. Do you think this
affected the movement of the dyes on the chromatography paper? Hint: Compare the Rf
values for the food dyes and candy shell dyes.
2.
Which color food dyes should not be used by persons allergic to FD&C yellow #5
(tartrazine)? Note that yellow #5 is yellow in color, but yellow #6 appears orange.
3.
Which color M&Ms, if any, should be avoided by persons allergic to tartrazine?
4.
How good were your original guesses concerning the makeup of the food dyes?
Submit a lab report consisting of:
a. cover sheet;
b. paragraph description of the procedure followed. Be specific concerning
methods used and adaptations which may have been necessary;
c. the chromatogram(s) prepared;
d. an analysis of the chromatogram(s) including measurements, Rf values and the
calculations of these values;
e. an analysis and evaluation of your results;
f. answers to the post-lab questions.
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