UNIT III: QUANTIFYING MATTER – THE MOLE
Mass of Substances:
A.
Atomic Mass:

Atomic Mass: is a mass ____________ between a sample atom and a ________________ atom.

Reference Atom: _________. (which has been analyzed by mass spectrometry to be exactly
12.0000amu)
The reference atom has changed throughout history – From H to O to C.
Example: Determining the Atomic Mass of one isotope of Chlorine:
a) Reference Atom 12C: 12.0000amu
b) Data given by Mass Spectrometer: Mass of Cl = 3
Mass of 12C
1
c) Therefore:
(The mass of 1 Cl is 3x that of
1C).
12.0000amu x 3 = 36.00 amu
Value of Cl on PT: 35.5 amu
This value is the ________________ mass of ALL the existing ________________ for Cl.

Atomic Mass Unit (amu): since the value of atomic mass is actually a ratio – It has ____ units.
We created a “_______________” unit for it called ___________.
B. Molecular Mass:


Mass of one _____________________ of a compound.
Calculated by adding the atomic masses of the contributing __________________.
Example: Ca3(PO4)2
The Mole & Molar Mass:


Since “amu” is a measurement that cannot be measured by any ____________________, scientists
decided to turn this unit into a unit that can be measured by an instrument. The “amu” has been
turned into grams.
To make this transition in units a valid one, scientists had to do the following:
a) Scientists determined using Mass Spectrometry, exactly how many 12C atoms there are in 12.0000g
of 12C:
12.0000g of 12C has 6.02 x 1023 atoms of 12C

Mole: a ______________ given to this number 6.02 x 1023.
6.02 x 1023 = 1 mole (________________________Number)

(Gravimetric) Molar Mass (GMM): the mass, in ___________, of 1 mole of a substance.
Example: Determine the molar mass of aluminum sulphate.
WATCH VIDEO’S #1 & 2 LINKED ON WEBSITE PAGE FOR THIS UNIT & TAKE NOTES BELOW
#1 – Introduction to Moles: https://www.youtube.com/watch?v=wI56mHUDJgQ&index=1&list=PL3hPm0ZdYhyxMcbHkcUgRlM4-w4gAgfRA
#2 -Counting Atoms: Intro to Moles Part 2: https://www.youtube.com/watch?v=hY7lzRBylSk&index=2&list=PL3hPm0ZdYhyxMcbHkcUgRlM4-w4gAgfRA
What is a Mole????
A Dozen =
A Mole =
Or in Sci. Not. A Mole =
How Big is This?
1 mole of Jellybeans =
Which is as big as
AVOGADRO’s Number
things
things
*impotant note: a mole is not
1 mole of doughnuts =
Which is as big as
1 mole of Sulphur atoms????? Lets explore this further in video #2
Counting Atoms Using Moles – How do I know that I have 1 mole of Sulphur atoms in the container???
How many atoms of C do I have in 31.87 g of C? Take Notes on Video Explanation:
Now Do it My Way!!! Using Unit Conversions !!! /4 points next class
Conversion Factor #1 – How many atoms are in a mole?
Conversion Factor #2 – How many g of C are in a mole of C? (molar mass)
Applying these we get: g of C given * conv. Factor #1 * conv. Factor #2 =
X
X
=
Calculations Involving Molar Mass:
Warm Up – Molar Mass of Molecules Practice 
Hebden p. 80- #6 or
WATCH VIDEO’S #3 On the Website:
WORKSHEET: Molar Mass Worksheet
Avogadro's Number (Mole) – Numberphile http://www.youtube.com/watch?v=2dzS_LXvYA0
1)
GMM:
__ grams
;
1 mole of a substance
1 mole of a substance
2) Avogadro’s Number:
6.02 x 1023
1 mole
__ grams
;
1 mole
6.02 x 1023
Example: Determine how many moles of sodium hydroxide there are in 3.62 x 1021 molecules of
sodium hydroxide.
Example: Determine how many atoms of lead there are in 2.56 moles of lead.
Example: Determine how many moles are in 82.6g of calcium phosphate.
HEBDEN p. 82 #8-10 or
WORKSHEET: Mole Intro Worksheet
A. Going from Atoms to Molecules:
In any given compound, there is a fixed # of atoms that make up that compound:
Total # of Atoms
1 molecule
Example: 1 molecule/compound of sodium sulphate has:
Example: How many atoms are there in 5 molecules of copper (II) sulphate pentahydrate?
Example: How many moles are there in 5 molecules of copper (II) sulphate pentahydrate?
Example: How many atoms are there in 8.2g of aluminum sulphate?
* Mole Worksheet #1 & 2
Determining an Unknown Compound’s Composition:


Chemists often have samples of compounds that they do not know the ____________________ of.
(Forensics usually encounter this problem).
The identity of the compound can be revealed in a combination of three steps:
a) Determining the Percentage Composition
b) Determining the Empirical Formula
c) Determining the Molecular Formula
A. Percentage Composition:
Percentage Composition: the __________ % of each of the contributing atom in a compound.
These % are often calculated for the scientist by an instrument called the
_____________________________________________.
Example: What is the % composition of oxalic acid? (pretend that we have to find these % manually).
1) Assume you have 1 mole of the compound – Determine the compound’s molar mass.
2) Determine the TOTAL mass for each contributing atom:
3) Determine the mass % of each atom compared to the compound’s total mass:
Example: Determine the % composition of ammonium chromate
COMMON MISTAKES – Watch Video - http://www.youtube.com/watch?v=lywmGCfIUIA
Error #1 –
Error #2 -
HEBDEN P. 91 # 44-45 OR
WORKSHEET: Percentage Composition Worksheet
B. Empirical Formula:
Watch Empirical & Molecular Formula Intro Video - http://www.youtube.com/watch?v=wnRaBWvhYKY
Empirical Formula: the smallest _________________________ ratio of ____________ that make up a
compound.
Example: C2H4, C3H6, C4H8, C5H10 (Molecular Formulas)
__________________ (Empirical Formula)
Example: What is the empirical formula of a compound that contains 80% C and 20% H?
1) Assume you have 100g of the compound. Convert to moles.
2) Divide the # of moles of each atom by the smallest mole value:
Example: A compound contains 58.5% C, 7.3% H and 34.2% N. What is the empirical formula of the
compound?
Example: What is the EF for a compound containing 81.8% C and 18.2% H?
PROBLEM! The # of H atoms is neither close to 2 nor 3. The 0.67 is actually 2/3. To eliminate the
denominator, we must multiply everything by ______.
.....Therefore:
NOTE: For the following decimal values, the equivalent fractions are given. The denominator must be
cancelled out by multiplying all answers by the appropriate value:
0.20 = 1/5
0.25 = 1/4
0.60 = 3/5
0.33 = 1/3
0.40 = 2/5
0.75 = 3/4
0.80 = 4/5
0.67 = 2/3
0.50 = 1/2
Example: What is the EF for a compound containing 39.0% Si and 61.0% O?
Example: Find the EF of 26.0g of cobalt chloride which decomposes to produce 11.96g of Co.
HEBDEN P. 93 #46 OR
WORKSHEET: Empirical Formula Worksheet
C. Molecular Formula:
Molecular Formula: is the _________________ of an ___________________________________.
Gives the ___________formula for a compound.
N =
GMM of Molecular Formula
GMM of Empirical Formula
...where N = the whole # multiple of the EF.
Example: A molecule has an EF of OH and a molecular GMM of 34.0g. What is its molecular formula?
1) Find N.
2) Multiply by the EF by the value of N to obtain the molecular formula.
Example: EF of a compound is SiH2. If 0.0275mol of the compound has a mass of 1.71g, what is the
molecular formula of this compound?
Watch Video – E.F. and M.F. from % - http://www.youtube.com/watch?v=ZiXtpuDZlP8
A sample was analysed as having 40.0% C, 6.71% H and 53.29% O. If the molecular weight of the compound is
180.16 g/mol what are the EF and MF of the compound?
WORKSHEET: Molecular Formula Worksheet
Formula of a Hydrate:
Hydrate: a solid ___________________________________ which contains ______ loosely bonded to its
structure.
Example: CuSO4.5H2O
ZnCO3.3H2O
Al2(SO4)3.6H2O
Ba(OH)2.8H2O
Hydrate
anhydrate + water
Example: A 15.00g sample of a hydrate was found to contain 7.05g of water. If the anhydrous form of
the salt is sodium sulphate, determine the formula of the hydrate.
1) Find the % composition of each part of the hydrate:
2) Determine the ratio for each part of the hydrate:
WORKSHEETS: * Formula of a Hydrate Worksheet
LAB: Empirical Formula of a Hydrate
* Empirical & Molecular Formulas Worksheet
Molarity – Concentration of a Solution
All of the substances dealt with thus far were ____________ substances (pure ________, ____________ or
____________). Most of the substances found in the lab however, are in the form of _________________).
A. What is a Solution?
Solution: a mixture of two pure substances, a solute and a solvent.
The solvent and solute do _________ undergo a reaction.
Solute: the pure substance that dissolves in the _________________.
Solvent: the pure _________________ (H2O) which the solute dissolves.
There are many types of solutions: a) Solid dissolving in a liquid
(Ex. Salt solution)
b) Two or more pure liquids mixing with one another (Ex. Metal alloys)
c) Two or more pure gases mixing with one another (Ex. Air)
B. Quantifying Solutions – Molarity
Molarity: the concentration of a solution – Defined as the number of moles of solute in 1L of solution.
M = mole
Example: The [NaCl] solution is 0.20M.
L
Watch – Calculating Molarity Practice & Take notes below - http://www.youtube.com/watch?v=SXf9rDnVFao
Calculate the molarity of a solution prepared by dissolving 9.8 moles of NaOH in enough water to make 3.62L of solution
You dissolve 152.5 g of CuCl2 in water to make a solution with a final volume of 2.25L. What is its molarity?
A solution contains 375 mL and contains 42.5g NaCl, what is its molarity?
Watch – Molarity Practice Problems Part 2 - http://www.youtube.com/watch?v=sWfn8hbXRp8
How many moles of NaCl are in 3.5L of a 1.5M solution of NaCl?
If you have 4.1 moles of glucose and want to make a 0.25 M solution with it, what will be the final volume of
the solution?
If a student has 35.0g of FeCl3 and needs to make 1.5 molar solution with it, what will the volume of the
solution be?
How many grams of NaOH do you have to dissolve to make 725 mL of a 2.5M solution?
A.
Calculating Concentration of a Solution: in class notes
Example: What is the [NaCl] in a solution containing 5.12g of NaCl in 25.0mL of solution?
Example: What is the mass of sodium hydroxide in 3.50L of 0.200M sodium hydroxide?
Example: What is the molarity of sulphuric acid, which has a density of 1.839g/mL?
Example: What is the [ ] of calcium chloride in a solution made by dissolving 15.00g of calcium chloride
hexa-hydrate to 500.0mL?
a) Determine the amount of solute in 15.00g of calcium chloride hexahydrate.
HEBDEN P. 98 # 59-70 or
B. Dilutions of Solutions:
BEFORE YOU START – DO #72-77 ON PAGE 99 HEBDEN
WORKSHEET: Molarity Worksheet
(i)
Dilution of one Solution:
Dilution: when more _________________ is added to an existing solution.
This lowers the _________________________ of the solution.
This does _______ change the number of ____________ of _________________ in the solution.
MiVi
=
MfVf
Example: A 250.00mL solution of aluminum phosphate has a [ ] of 2.50M. 500.00mL of water is added
to the solution. What is the final [ ] of the solution?
Example: A farmer is mixing a solution of fertilizer for his tomato crop. He takes 15.0g of ammonium
nitrate and dissolves it in 25.0mL of water. After spraying his tomatoes with this solution,
the leaves turned yellow! It was too concentrated! He decides to add another 2.5L of water
to the solution. What is the final [ ] of the solution?
HEBDEN P. 102 #78-83 OR
WORKSHEET: Dilution Worksheet
(ii)
Dilution by Mixing 2 or More Solutions:
Example: What is the [ ] of each ion in a solution of 0.25M aluminum chloride?
1) Write the balanced dissociation equation:
2) Use the mole ratio in the balanced equation to find the [ ] of each ion.
Example: If 300.0mL of 0.250M NaCl is added to 500.0mL of 0.100M NaCl, what is the final [Na +] and
final [Cl-1] for the mixture?
1) Find the moles of each solution independently.
2) Add the moles of any common ions together.
3) Find the diluted concentration.
Example: What is the final [ ] of each of the ions when 50.0mL of 0.240M aluminum bromide and
25.00mL of 0.300M calcium bromide are mixed?
WORKSHEETS: * HEBDEN P. 102 # 84-94 or Dilutions with Two or
More Solutions Worksheet
* Mole Review Package
LAB: Dilution of Solutions Lab
* HEBDEN P. 103 # 95-102 OR Molarity Review Package