PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS
Learning Activity 4cd: Lab – Ionic and Covalent Compounds
Unit E: Matter and its Interactions
Learning Targets:
4c) I can gather, analyze and interpret data about physical and chemical properties to develop a prediction and
support a claim about the type of bond in a compound (ionic, polar covalent, nonpolar covalent). (DOK 2-3)
4d ) I can describe how physical and chemical properties of substances provide evidence for our current bonding
models. (DOK 1-2)
Properties of Ionic and Covalent Compounds
Introduction:
A compound is defined as the chemical combination of two or more elements. A chemical bond is the “glue” that holds
atoms of different elements together. Bonds in compounds can be classified into two general types: ionic and covalent. Ionic
bonds generally occur between a metallic atom and a nonmetallic atom. The ionic bond involves the transfer of electrons from
the metallic atom to the nonmetallic atom, resulting in a charge difference. The positively charged metal ion is then attracted
(electrostatic attraction) to the negatively charged nonmetal ion. Covalent bonding generally occurs between atoms that are
nonmetallic and it involves the sharing of electrons.
Properties such as melting point, boiling point, solubility, electrical conductively, color, and odor are some of the
properties that can help you distinguish ionic from covalent compounds. In this experiment, you will observe several properties
of some ionic and covalent compounds and attempt to recognize some patterns among the properties. It is important to
understand that the patterns are generalizations that do not necessarily apply to ALL ionic and covalent compounds.
Purpose:
In today’s experiment, you will observe some properties of ionic and covalent compounds. You will compare the
names, formulas, solubility, electrical conductivity, and relative melting points of four KNOWN compounds. You will
use the observed properties to classify the known compounds and will apply your understanding to identify several
unknowns.
Materials:
TEST B
distilled water
10 mL graduated cylinder
6 small test tubes
test tube rack
6 stoppers for test tubes
safety goggles
lab apron
6 labeled plastic cups with lids, each containing 1 gram of the identified substance.
TEST C
contents of tt from Test B
watch glass
conductivity tester
[OPTIONAL TEST D]
[6 small test tubes]
[test tube rack]
[6 stoppers for test tubes]
[99% isopropyl alcohol]
[ (isopropanol, 2-propanol) ]
TEST E…………………
coffee can lid
aluminum foil
small test tube
crucible tongs
stop watch, if available
hot plate
Chemicals:
NAME
sucrose (table sugar)
FORMULA
C12H22O11
sodium chloride (table salt)
NaCl
sodium citrate
Na3C6H5O7
4
sodium hydrogen carbonate
(baking soda)
NaHCO3
5
Glycerol
(also called glycerine)
C3H8O3
Paraffin wax
C20H42
1
2
3
6
USE(S)
sweetener; add texture to baked products;
preservative in jams;
enhances taste of food; preservative
treatment of kidney stones; food additive for flavor
(has a tart taste); preservative; anti-coagulant;
occurs naturally in citrus fruits and berries
leavening agent in cooking; cleaning; disinfectant;
toothpaste; absorb odors; antacid
in foods as humectant, solvent, and sweetener,
filler, thickening agent, and may help preserve
foods; sugar substitute; in medicine as a lubricant
and humectant; in lotions; glycerine soap; in
botantical extracts; used to be used in anti-freeze;
candle-making; coatings for waxed paper or cloth;
candy making; coating for cheese; chewing gum
additive; crayons; in wax for surfboards, skis, and
snowboards
PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS
Safety Considerations:
TEST E - ALWAYS exercise caution when using hot plates. The aluminum foil will be very hot after TEST E of this
experiment. Be careful.
Waste Disposal:
All solutions (solids dissolved in liquids) used in today’s experiment can be flushed down the sink with running
water. Any solids that do not dissolve should be wrapped in a small amount of paper towel and thrown away in the
regular trash can.
Procedure:
1.
2.
Read the procedure, being certain you understand what you will be doing in the lab. Ask questions if you
don’t understand. While you are reading the procedure, you need to develop a Data table* to organize the
information you will collect during this investigation.
Once you have shown your teacher the data table, put on your laboratory apron and safety goggles.
TEST A: GENERAL CHARACTERISTICS
3.
Open each plastic container and make some general observations of each substance. Include state of
matter (solid, liquid), color, texture, odor, and conductivity of the pure substance.
TEST B: SOLUBILITY in WATER
4.
Label six test tubes with numbers 1-6 to correspond to the substances in your data table. Place 5 mL of
distilled water in each of the test tubes. Then put about ½ gram* of each of the substances into the
appropriate test tube. [Remember – the cup contains 1 gram, so put ½ of the amount you have in the portion
cup into the test tube.] Stopper the tubes and shake them to dissolve the solids as much as possible. Shake
for one to two minutes. Do not clean up the test tubes yet – you will need them for Test C.
 If the substance dissolves, record this as soluble
 If the substance does NOT dissolve, record this as insoluble.
 If some of the substance dissolves, but not ALL of the substance dissolves, record this as partially
soluble.
TEST C: ELECTRICAL CONDUCTIVITY OF WATER MIXTURE
5.
6.
Determine the electrical conductivity of any of the water mixtures where the pure substance dissolved.
[If a substance did not dissolve, there is no need to test the conductivity of the water mixture.]
Electrical conductivity can be tested by using a conductivity tester. Pour a small amount of one water mixture
on a watch glass. Place the electrodes of the conductivity tester into the mixture and turn the tester on. If the
mixture conducts electricity, the LED will light. If the mixture does not conduct electricity, the light will not go
on. Use the chart on the back of the conductivity tester to determine the degree of conductivity. Record the
results in your data table. Carefully rinse the electrodes and watch glass with distilled water before testing the
next mixture.
Rinse the test tubes, stoppers, and watch glass. Check with your teacher for the proper disposal of the
mixtures.
OPTIONAL TEST D: SOLUBILITY in ISOPROPYL ALCOHOL
7.
8.
Place 5 mL of isopropyl alcohol in each of the test tubes. Dispose of any leftover alcohol carefully, following
your teachers guidelines. Then put ½ gram of each of the solids into the appropriate test tube. [Remember –
you massed out 1 gram initially… so put ½ of the amount that was originally in the portion cup into the test
tube.] Stopper the test tubes and shake them for one to two minutes. If the substance dissolves, it is soluble,
if not, it is insoluble. Record the results in your data table as soluble or insoluble. [Note: some substance may
appear to partially dissolve. Record these as partially soluble.]
Check with your teacher for the proper disposal of the solutions and the undissolved mixtures. [Take your test
tubes to the hood. Pour the contents of each of the test tubes into the appropriate beaker.] Rinse the test
tubes and stoppers at your sink.
PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS
TEST E: MELTING TIME
Melting time is the amount of time necessary to melt a certain quantity of a solid. This does not give an accurate
value for the melting point, but will enable you to see differences among the compounds. If the melting time is short,
the substance has a relatively low melting point. If the melting time is long, the substance has a relatively high
melting point. NOTE – If the substance is already a liquid, the melting point is low and there is no need to test it.
9.
Locate a hot plate, plug it in, and turn it on medium. Determine the “melting time” of the solids by placing a
small amount (sample about the size of a match head) of solid in an aluminum cup. (Make the aluminum cup
by forming a small square of aluminum foil around the bottom of a test tube. Remove the foil and flatten the
bottom of the cup.) Place the cup on the metal coffee can lid – in the appropriate spot.
[NOTE: The coffee can lid has been separated into six sections, with each section labeled with a number to
match the four substances to help you keep track. Once you have all six substances placed on the coffee can
lid, carefully place it on top of the hot plate and note the start time. Watch the samples carefully. Whenever a
sample starts to melt, immediately remove it from the coffee can lid using a crucible tong. Do NOT continue
heating these substances after they have melted. Record the melting time in your data table. Continue
heating the substances until they melt or until you reach 3 minutes. If a substance has not melted within the 3
minute time period, stop heating and record the melting time as > 3 minutes – which implies a high melting
point.
10.
11.
Once the samples have cooled, simply close the aluminum cups and discard them in a trash can.
Wash your hands thoroughly with soap and water.
UNKNOWN:
A student tested the following unknowns and collected the following data:
For ONE of the unknowns below, decide if the unknown is an ionic or covalent compound. Make a claim,
support it with evidence from the data table and explain how the properties (your evidence) relate to the
bonding.
NAME
FORMULA
A
B
C
D
alum
(aluminum potassium sulfate)
AlK(SO4)2·12H2O
phenyl salicylate (salol)
(C6H4OH)(COO(C6H5) or
C13H10O3
stearic acid
CH3(CH2)16COOH
dextrose
C6H12O6
NAME
B
alum
(aluminum potassium sulfate)
phenyl salicylate (salol)
C
stearic acid
D
dextrose
A
TEST
A
TEST
B
TEST C
TEST
E
White solid
Does not conduct
electricity
Dissolves
(soluble)
Conducts
electricity
High
melting point
White solid
Does not dissolve
(insoluble)
White solid
Does not dissolve
(insoluble)
White solid
Dissolves
(soluble)
Does NOT
conduct
electricity
Does NOT
conduct
electricity
Does NOT
conduct
electricity
low
melting point
low
melting point
low
melting point
USE(S)
deodorant; water purification, in styptic pencils (stop bleeding due to small cuts
when shaving); pickling;
once used in sunscreens; manufacture of some polymers, lacquers, adhesives,
waxes and polishes.
production of detergents, soaps, and cosmetics such as shampoos and shaving
cream products
simple sugar used in baking goods; added to artificial sweeteners as a filler.
PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS
Post Lab Discussion:
You have just recorded several properties of some ionic and covalent compounds. Up until now, you have
not identified the substances as ionic or covalent. Ionic compounds are generally made up of metallic and
nonmetallic elements, with the metal giving up electrons to the nonmetals. Covalent compounds are generally
made up of atoms that are nonmetallic, with the atoms sharing electrons.
You will need to refer to the ‘BACKGROUND INFORMATION’ in this lab, your notes, a textbook or another
resource to help you in determining whether the compounds used in this experiment are ionic or covalent. It is
important to emphasize that some of the results of the experiment may not reflect particular patterns.
Post Lab Analysis: Answer these questions in complete sentences so that the initial question is obvious.
(1)
After reading the background information (or other resource(s)), construct a Venn Diagram for Ionic and
Covalent Compounds.
Place at least 10 of the following descriptors in your Venn Diagram:
(a)
contain metal and nonmetal atoms
(b) contain nonmetal atoms
(c)
electrons are transferred from metals to nonmetals
(d) electrons are shared
(e) low(er) melting point
(f)
high(er) melting point
(g) soluble in water
(h) not soluble in water
(i)
solids do not conduct electricity
(j)
conduct electricity when dissolved in water
(k)
do not conduct electricity when dissolved in water
(l)
tend to be solids only
(m) tend to be gases, liquids, or soft solids
(n) tend to have distinct odors
(o) tend to have a crystal structure
Feel free to add additional descriptors to your diagram.
Use your lab observations and understanding, answer the following questions with a CLAIM, some EVIDENCE,
and – if possible – an EXPLANATION.
(2)
(3)
(4)
Which ONE known substance are you most sure is ionic? Why?
Which ONE known substance are you most sure is covalent? Why?
Which ONE known substance are you not sure if it is ionic or covalent? Why?
(5)
Place each of the six substances from this lab into your Venn diagram by writing each formula in the correct
part of the diagram.
Conclusion:
Write a paragraph that summarizes the big ideas from this lab. Include and underline the following terms in your
paragraph: Get the paragraph stamped by your teacher.
Ionic compound
Metal
Physical Properties
Electron(s)
Share
Transfer
Covalent Compound
Non-metal
PLEASE – do NOT write on this paper. RETURN this paper at the end of the class period. THANKS
Background Information:
Ionic compounds (or salts) are formed when metals transfer electrons to nonmetals. The loss of
electrons by the metal atom transforms it into a positive ion. The gain of electrons by the nonmetal atom
transforms it into a negative ion. The positive and negative ions are attracted to each other because of
their opposite charges. A salt is really a network of positive and negative ions that are stacked in a
specific crystalline structure due to their mutual attractions.
In a covalent compound, atoms share electrons. Covalent bonds are usually formed between
nonmetal atoms, which have more valence electrons than they are energetically capable of losing.
When two nonmetal atoms meet they do not tend to completely transfer electrons (as a metal would do
to a nonmetal); instead, they tend to share. One pair of electrons makes a covalent bond, and since both
atoms “want” that pair of electrons, they stick together as long as the pair is shared.
Both types of chemical bonds exist because of atoms trying to satisfy the octet rule. The octet rule says
that atoms gain, lose, or share electrons in an attempt to achieve the same electron configuration as one
of the noble gases (which usually have 8 valence electrons – hence the word “octet”). Noble gases have
the most stable arrangements of electrons; this explains why they so seldom participate in chemical
reactions.
If you know the chemical formula of a compound, you can predict whether it contains ionic bonds,
covalent bonds of a mixture of bond types. Nonmetals bond to each other via covalent bonds while
oppositely charged ions, such as metals and nonmetals, form ionic bonds. Some compounds have a
metal and several non-metals. These compounds (i.e. MgSO4 or Na3PO4) may have both ionic and
covalent bonds.
But, how do you know if a compound is ionic or covalent just by looking at a sample? This is where the
properties of ionic and covalent compounds can be useful. Because there are exceptions, you need to
look at several properties to determine whether a sample is ionic or covalent, but here are some
characteristics to consider:




Most crystals are ionic compounds. This is because the ions in these compounds tend to stack
into crystal lattices to balance between the attractive forces between opposite ions and the
repulsive forces between like ions. Covalent or molecular compounds can exist as crystals,
though. Examples include sugar crystals and diamond.
Ionic compounds tend to have higher melting and boiling points than covalent compounds.
Ionic compounds tend to be hard and brittle while covalent compounds tend to be softer and
more flexible.
Ionic compounds conduct electricity when dissolved in water while covalent compounds typically
don't. This is because covalent compounds dissolve into molecules while ionic compounds
dissolve into ions, which can conduct charge.
[Resource: http://chemistry.about.com/b/2013/07/25/properties-of-ionic-and-covalent-compounds.htm]