Chemistry
Name:
09.02.1a
Date:
Stoichiometry: Ideal Calculations
Purpose
The purpose of this activity is to calculate the moles and/or mass of a reactant or product in a
chemical reaction.
Background
We use stoichiometric calculations when one wants to calculate the amount of product formed by
a chemical reaction, or the amount of a reactant needed in a chemical reaction.
For example, how many grams of water can be made from 100. g of hydrogen gas? We use
dimensional analysis is used to solve stoichiometric calculations!
Model
Question: How many grams of water can be made from 100. g of hydrogen gas? (Assume an
unlimited supply of oxygen gas.)
Steps.
1. Write the balanced chemical equation.
2H2 + 1O2  2H2O
2. Identify:
A. What you know (where you are starting) ............................................................... 100. g H2
B. What you want to know (where you want to end) ............................................ X g of water
3. Set up the skeletal dimensional analysis equation:
100. g H2 x -----------------------
= X g H2 O
4. Identify the conversion factor. This allows you to change the units from the known to the
unknown substance. The most common conversion factor in stoichiometric calculations is
mass-to-mass of different chemicals. E.g., mass H2  mass H2O). Sometimes, you may
need to convert between mass, moles, volume, and particles (atoms or molecules). ALL
stoichiometric calculations go through molesA to molesB.
100. 𝑔 𝐻2
𝑥
𝑥
𝑚𝑜𝑙 𝐻2 𝑂
𝑥
𝑚𝑜𝑙 𝐻2
= 𝑋 𝑔 𝐻2 𝑂
5. The unit in the denominator for the first step is the same as the unit you start with.
100. 𝑔 𝐻2
𝑚𝑜𝑙 𝐻2 𝑂
𝑥
𝑥
𝑥
= 𝑋 𝑔 𝐻2 𝑂
𝑔 𝐻2
𝑚𝑜𝑙 𝐻2
6. Convert this to the conversion factor units: g H2  mol H2.
100. 𝑔 𝐻2
𝑚𝑜𝑙 𝐻2
𝑚𝑜𝑙 𝐻2 𝑂
𝑥
𝑥
𝑥
𝑔 𝐻2
𝑚𝑜𝑙 𝐻2
Document1
= 𝑋 𝑔 𝐻2 𝑂
Stoichiometry – Ideal Calculations
Chemistry
p. 2
7. Fill in all of the other values and units needed. Make sure all of the units cancel out except
the one you want in the answer.
100. 𝑔 𝐻2
1 𝑚𝑜𝑙 𝐻2
2 𝑚𝑜𝑙 𝐻2 𝑂 18.02 𝑔 𝐻2 𝑂
𝑥
𝑥
𝑥
= 𝑋 𝑔 𝐻2 𝑂
2.02 𝑔 𝐻2
2 𝑚𝑜𝑙 𝐻2
1 𝑚𝑜𝑙 𝐻2 𝑂
100. 𝑔 𝐻2
𝑥
1 𝑚𝑜𝑙 𝐻2
2.02 𝑔 𝐻2
8. Perform the calculations.
100. 𝑔 𝐻2
1 𝑚𝑜𝑙 𝐻2
𝑥
2.02 𝑔 𝐻2
𝑥
𝑥
2 𝑚𝑜𝑙 𝐻2 𝑂 18.02 𝑔 𝐻2 𝑂
𝑥
2 𝑚𝑜𝑙 𝐻2
1 𝑚𝑜𝑙 𝐻2 𝑂
2 𝑚𝑜𝑙 𝐻2 𝑂 18.02 𝑔 𝐻2 𝑂
𝑥
2 𝑚𝑜𝑙 𝐻2
1 𝑚𝑜𝑙 𝐻2 𝑂
= 𝑋 𝑔 𝐻2 𝑂
= 892 𝑔 𝐻2 𝑂
9. Check:
H2 is much lighter than H2O, so the mass of H2O should be less.
Problems
Directions: Complete all the steps shown in the model problem above when you write your
answers with the correct units and significant figures.
1. HW 7-1 Read Sections 9-1 and 9-2 Questions 1-2 Page 305
2. How many grams of lithium oxide can be produced from 32.04 g of lithium and an unlimited
amount of oxygen?
3. What mass of sodium chloride is produced when chlorine reacts with 0.29 g of sodium?
4. Determine the mass of carbon dioxide produced when 0.850 g of butane (C4H10) burns.
5. Hydrogen reacts with oxygen in a synthesis reaction to make water. If you have 2.99 g of
oxygen how many grams of hydrogen do you need?
6. Lead (II) oxide reacts with hydrochloric acid in a double displacement reaction. How many
grams lead (II) chloride will be produced if you have 0.79 g of lead(II) oxide?
7. Hydrochloric acid and 50.0 grams of iron(III) sulfide react. What mass of dihydrogen
monosulfide gas is produced?
8. How many grams of nitric acid is needed to react completely with 25.0 grams of magnesium
in a single replacement reaction?