Name: ________________________________ Section: _______ Version: _________
Chemistry Study Guide
Mass to Mass Conversions
On your next chemistry test, you will be asked questions similar to this one:
The equation for sugar burning in the presence of oxygen is
C6H12O6 + 6O2 → 6CO2 + 6H2O
If 37.6g of sugar is burned, what mass of water vapor will be produced?
It this kind of question, there is always a known substance and an unknown substance.
Solving it is easy, but involves several steps. The steps are:
a. Convert grams of known into moles of known.
b. Convert moles of known into moles of unknown.
c. Convert moles of unknown into grams of unknown.
In the above question, the known substance is sugar, because you know that you have
37.6g of sugar. The unknown substance is water, because you are being asked what mass
of water will be produced. So the steps are:
a. Convert grams of sugar into moles of sugar.
b. Convert moles of sugar into moles of water.
c. Convert moles of water into grams of water.
You will practice each step by itself. You may work with a partner or in a group.
Start with Step 1: Converting grams to moles.
When you feel you understand and have mastered it, check your answers and then request
Step 2.
Name: ________________________________ Section: _______ Version: _________
Chemistry Study Guide
Mass to Mass Conversions
Step 1.
Converting grams to moles.
Example problem:
You have 24g of carbon. How many moles of carbon atoms do you have?
moles
grams x --------- = moles
grams
1 mole
24g x ---------- = 2 moles
12g
You know that 1 mole of carbon atoms has a mass of 12g because the Periodic
Table tells you that the atomic mass of carbon is 12.
You know that you multiply by moles/grams and not grams/moles because the
units have to cancel out.
Practice problems:
1. You have 8g of helium. How many moles of helium atoms do you have?
2. You have 270g of aluminum. How many moles of aluminum atoms do you have?
3. You have 30g of hydrogen gas with the formula H2. How many moles of hydrogen
molecules do you have? (hint: Each molecule includes two atoms.)
4. You have 90.1g of water. How many moles of water molecules do you have?
5. You have 22g of carbon dioxide (CO2). How many moles of CO2 do you have?
6. You have 137.62g of sulfur dioxide (SO2). How many moles do you have?
7. You have 700g of sulfuric acid (H2SO4). How many moles do you have?
8. How many moles are in 15g of NaOH?
9. 500g of C10H8 is equal to how many moles?
10. You have 37.6g of sugar (C6H12O6). How many moles is that?
Name: ________________________________ Section: _______ Version: _________
Chemistry Study Guide
Mass to Mass Conversions
Step 2.
Converting moles to moles.
Example problem:
2H2 + O2 → 2H2O
You start with 5 moles of hydrogen gas. How many moles of water are produced?
How many moles of oxygen are consumed?
mol known x ratio unknown/known = moles unknown
5 mol H2 x 2/2 = 5 mol H2O
5 mol H2 x 1/2 = 2.5 mol O2
You know that the ratio of H2O to H2 is 2/2 because the balanced equation shows
two molecules of H2O and two molecules of H2.
You know that the ratio of O2 to H2 is 1/2 because the balanced equation shows
one molecule of O2 and two molecules of H2.
Practice problems:
1. CH2O + O2 → CO2 + H2O
One mole of O2 is consumed. How many moles of CO2 are produced?
2. 3AL2Si2O5 → Al6Si2O13 + 4SiO2 + 6H2O
Nine moles of AL2Si2O5 react. How many moles of Al6Si2O13 are produced?
3. TiO2 + C + 2Cl2 → TiCl4 + CO2
You start with three moles of TiO2. How many moles of Cl2 do you need?
4. TiO2 + C + 2Cl2 → TiCl4 + CO2
You start with three moles of TiO2. How many moles of TiCl4 will be produced?
5. NH4NO3 → N2O + 2H2O
146.93 moles of NH4NO3 decompose to produce how many moles of N2O?
6. NH4NO3 → N2O + 2H2O
146.93 moles of NH4NO3 decompose to produce how many moles of H2O?
7. 2NaN3 → 2Na + 3N2
This reaction produces 20 moles of sodium metal. How many moles of nitrogen
gas does it produce?
8. C6H12O6 + 6O2 → 6CO2 + 6H2O
0.2 moles of sugar are burned. How many moles of water vapor are produced?