SCH4C1 – Unit 3 Booklet
Name:__________________
QUANTITIES IN CHEMISTRY
BIG QUESTIONS:
1. What are some of the ways to measure chemicals?
2. Why is measuring important?
Expectations – By the end of this unit, you should be able to:
o Count atoms in chemical compounds
o Balance chemical equations using co-efficients
o Use basic math skills to calculate quantities in chemistry
o Effectively use SI units in calculations
o Understand the concept of the mole
o Calculate the percentage composition of a compound and apply this concept to real life situations.
o Understand how a chemist would measure their precision in the lab
o Understand how chemists can predict quantities of chemicals produced in a reaction
o Understand how we measure the concentration of a solution
o Understand how to prepare a solution with a specific concentration using dilution.
Unit 3 Timeline:

Chemical Calculations – Day 1 – Counting atoms review, Balancing Equations

Chemical Calculations – Day 2 – The mole and number of particles calculations

Chemical Calculations – Day 3 – Mass and Molar Mass

Chemical Calculations – Day 4 – Percent Composition

Chemical Calculations – Day 5 – Percent Compostion lab

Chemical Calculations – Day 6 – Basic Math and Solving Ratios

Chemical Calculations – Day 7 – The mole and Mole Krispies lab

Chemical Calculations – Day 8 – Mole Ratios

Chemical Calculations – Day 9 – Predicting Mass from Mole Ratios

Chemical Calculations – Day 10 – % Error, % Yield, Mass to Mass Lab

Chemical Calculations – Day 11 – Finish lab, Introduction to Solutions

Chemical Calculations – Day 12 – Dilution and Concentration, lab

Chemical Calculations – Day 13 – Review and Practice Test

Chemical Calculations – Day 14 – Unit Test
SCH4C1 – Unit 3 – Chemical Calculations:
Name:_______________________________
Counting Atoms:
Subscripts:
KNO3
#K_________
#N_________ #O________
Brackets:
Mg(OH)2
# Mg_______ #O_________ #H_________
Co-Efficients:
2CO2
#C_________
#O_________
Try these:
2Mg(OH)2
BaNO3
Mg
Ba
O
N
H
O
4PbCl4
Na2Cr2O7
Pb
Na
Cl
Cr
O
3H2SO4
5NH3
H
N
S
H
O
Balancing Equations
Skeleton equations just show the ________________ and ___________________ molecules.
Example:
BUT In chemical equations, the number of atoms on the reactants side of a reaction has to be
__________________to the number of atoms on the products side. We need to __________________ the equation.
Most skeleton equations are not balanced. We do this by adding whole ____________________ to either side of a
reaction. These are shown as ________________________ in the equation.
Examples:
Reactants
Products
N
H
__________N2 + ___________H2  ______________NH3
Reactants
Products
H
_________H2 + ____________O2 ______________H2O
O
Reactants
Products
Na
_______ Na + _______ N2

_______ Na3N
Try These:
1. _______ Al + ________ Fe3N2
2. _______ ZnS + ________AlP 
3. ______ NaClO3


_________ AlN + ________ Fe
_______ Zn3P2 + ________Al2S3
________ NaCl + _________ O2
N
4. ________ Ag2S

________ Ag + _______S8
5. _______ Br2 + _______KI

6. _______ C3H6 + _______ O2

_______ H2O + ________CO2
7. ________ AgNO3 + ________ CaI2

________ AgI + ________Ca(NO3)2
8. ______ Ba(NO3)2 + _______Na2S

________ BaS + ________NaNO3
9. __________Al(NO3)3 + ________Mg 
_________KBr + ________ I2
________Mg(NO3)2 + _________ Al
*challenge problem*
Chemical Quantities:
Number of Particles:
Sometimes it is useful to be able to count the number of ___________ or _________________ in a sample of a
chemical. Remember that particles are very small, so these numbers will be very large. We use the symbol ______ to
represent number of particles in a calculation.
The Mole:
The mole is a useful way of measuring chemicals. One mole represents a set number of particles, and does not
depend on what the substance is. In calculations the symbol for the number of moles is ________.
Analogy:
12 donuts is equal to one dozen.
602,200,000,000,000,000,000,000 particles are equal to one mole.
The big number above is called ____________________________ _________________. An easier way to write this is
in scientific notation. It’s ____________________. On your calculator, you need to use the exponent button to do this
(ask me if you need to know how to do this on your calculator!).
Moles, particles and Avogadro’s number are related with the following triangle, which you can use to do calculate
one of the three quantities (if you know the other two).
Examples:
If there are 5.5x1024 molecules of beryllium in a sample, how many moles are there?
If there are 3.45 moles of helium gas in a balloon, how many helium atoms are there in the balloon?
Try these:
How many moles of Uranium are in a 3.45x1022 atom sample?
How many atoms are in 0.15 moles of lithium?
Mass:
Mass is easy to measure in class using a ________________ (scale). We measure mass in _______ and the symbol we
will use in calculations is _________.
Molar Mass:
The molar mass of an atom is found ______________________________________________________________. It
represents the ____________ of one mole of the substance. The symbol for molar mass in calculations is _________
and it is measured in _____________.
Examples:
M of Carbon= _______________
M of Lead = ____________
M of Uranium = _______________
You can also find the molar mass of a compound by _________________________________________________.
Examples:
M of CO2 = _________________
M of H2O = _____________________
The mass, molar mass, and number of moles are all related by the following triangle which allows you to calculate
one quantity if you know the other two.
Examples:
1. How many moles of potassium are in a 12 gram sample?
2. How many grams of U2O5 are in 1.5 moles?
Try these!
1. How many moles of NaOH are in a 60 gram sample?
2. How many grams are in 13 moles of O2 gas?
Percent Composition:
Percent composition:
Steps to find the percentage composition by mass of a substance:
Example: CO2
1. Find the molar mass of each element individually.
2. Find the molar mass of the whole compound.
3. Divide the element’s M by the compound’s M. You need to do this once for each element.
4. Multiply your results by 100%.
5. Check to make sure that all the percents add up to 100.
Try these:
1. Find the percent composition of each element in NaCl.
2. Find the percent composition of each element in BaCl2.
Some Basic Math You May Need:
Equivalent Ratios:
5 : 16 = 12 : y
Examples:
If 12 cookies take 2 cups of chocolate chips to make, how many cookies can you make with 3 cups of chocolate chips?
If 1 kg of carbon will create 3.5 kg of carbon dioxide, how much carbon dioxide will 15.5 kg of carbon make?
Sodium and chlorine react in a 2 : 3.5 ratio by weight. How much sodium do you need to react with 12 kg of chlorine?
Try these:
1. Blood contains a ratio of red cells to white cells of 98:2. How many white blood cells are there in a sample
that contains 160,000 red blood cells?
2. A sample of rock contains calcium and carbon in a 3.3 : 1 ratio. How much calcium is there if there is 15 kg of
carbon?
Stoichiometry - Mole Ratios:
Balanced chemical equations tell us the _________________ of chemicals in a _____________________.
This ratio is by _____________, not by ______________.
Example 1:
In the reaction 2H2 + O2  2H2O
_________ moles of hydrogen react with ___________ mole of oxygen to make _________ moles of water.
If you had 3 moles of hydrogen, how many moles of oxygen would you need?
How many moles of water could you make?
Example 2:
In the reaction 4Fe + 3O2  2Fe2O3
What is the mole ratio of Iron : Oxygen?
______________________
What is the mole ratio of Iron: Iron (III) Oxide? ______________________
How many moles of iron reacted to make 4.5 moles of Iron (III) oxide?
Try this!
1. Balance this reaction:
________ Ag + ________S2  ___________Ag2S
If you had 1.4 moles of silverware in your drawer, and it tarnished (reacted with sulphur), how many moles of silver
sulphide would be produced?
How many moles of sulphur were pulled from the air?
Calculating Moles From Mass – Advanced Stoichiometry
You have 22 g of copper. How many moles of copper do you have? (Hint: you need to use the molar mass)
You want to react the copper with HCl to make some copper (II) chloride. Balance this equation.
_____________Cu + ________________HCl  _______________H2 + _______________CuCl2
Use the mole ratio to figure out how many moles of HCl you will need to react with your Copper.
Use the molar mass of HCl to figure out how many grams of HCl you will need.
Use the mole ratio to figure out how many moles of CuCl2 you can produce.
Use the molar mass of CuCl2 to figure out how many grams of CuCl2 you can produce.
Limiting Reagents? What Runs Out?
We are rarely able to mix chemicals in exact mole ratios. Sometimes you will run out of one chemical. This is called
your ______________________ reagent.
Example:
You are mixing 3 moles of Hydrogen (H2) with 2 moles of Nitrogen (N2) to make ammonia (NH3). Which runs out first?
1. Balance the chemical equation. Do not use the moles given in the question (yet!)
__________N2 + ____________H2  _______________NH3
2. Now look at the mole ratio. Which chemical do you have left over? This is called your ___________________
reagent.
Example 2:
You are mixing 5 moles of Hydrogen (H2) with 4 moles of oxygen (O2) to make water. Which runs out first?
1. Write an equation and balance it.
2. Figure out which will run out from the mole ratio.
Try this:
You have 4 moles of Aluminum (Al) and 5 moles of chlorine gas (Cl2) and you are trying to make Aluminum chloride
(AlCl3). Which runs out first?
Concentration and Dilution:
Concentration is a measurement of how much of a chemical is in a given __________________. It is usually measured
in _________________________________ (mol/L).
You can use the following triangle to calculate concentrations, number of moles, or volume when you know the other
two.
Examples:
1. You have 3 moles of sulphuric acid, and 5 litres of water to mix it in. What will the concentration be of the
resulting solution?
2. You want to make a 0.5 mol/L solution of copper chloride. You have 3.5 moles. How much water do you
need?
3. You want to make a 1.5 mol/L solution of hydrochloric acid. You have 0.75 L of water. How many moles of HCl
do you need?
4. What is the concentration of the solution made by dissolving 100 g of NaCl in 1L of water? (You need to use
mass to find moles first!!! Use n=mass/molar mass)
Dilution is the process of adding water to a solution. Your ____________________ goes _______________ because
the volume goes up and moles stay the same.
Examples:
1a) You have 1 L of a 4 mol/L solution. How many moles do you have?
b) What is the new concentration if you dilute the solution to 3L?
2a) You have 0.75L of a 0.4 mol/L solution. How many moles do you have?
b) What is the new concentration if you dilute the solution to 2L?
3a) You have 1L of a 0.1 mol/L solution . How many moles do you have?
b) You boil off some water until there is only 0.2 L remaining. What is the new concentration? (Concentration should
go up because volume went down).