A mass to mass probelm is one in which the mass of a reactant
or product is given. You are then asked to calculate the mass
of another reactant required or the mass of another product formed.
Example 1:
How many grams of oxygen are required to burn 12.9
grams of propane, C3H8?
Sample solution:
Step 1
Write the equation, the moles and masses of the substances
beneath the required substances.
|
C3H8 |
+ |
5O2 |
-----> |
3 CO2 |
+ |
4 H2O |
|
1 mole |
|
5 moles |
|
|
|
|
|
44 g |
|
5 (32) g |
|
|
|
|
Step 2
Write the given value (12.9 g propane) and "X" for the unknown (oxygen)
beneath the appropriate substance.
|
C3H8 |
+ |
5O2 |
-----> |
3 CO2 |
+ |
4 H2O |
|
1 mole |
|
5 moles |
|
|
|
|
|
44 g |
|
5 (32) g |
|
|
|
|
|
12.9 g |
|
X |
|
|
|
|
Step 3
Set up a ratio.
Step 4
Solve for "X". Use cross multiplication.
X = (2064 g )
/ 44 g
= 46.9 g
Therefore 12.9 grams of propane will produce 46.9 grams of oxygen.
Example 2:
Nitrogen and hydrogen react to produce ammonia. What mass
of ammonia could be produced from 500 grams of nitrogen?
Assume that enough hydrogen is available for a complete reaction.
Sample solution:
Step 1
Write a balanced chemical equation and the number of moles
and the masses of all the substances in the equation.
| _ N2 |
+ |
_ H2 |
-----> |
_ NH3 |
| mol |
|
|
|
mol |
| g |
|
|
|
g |
Step 2
Write the given value and "X"
for the unknown beneath the appropriate substance.
| _ N2 |
+ |
_H2 |
-----> |
_ NH3 |
|
28 g |
|
_ (2 ) g |
|
_ ( 17 ) g |
| |
|
|
|
|
Step 3
Set up a ratio.
Step 4
Solve for "X".
Use cross multiplication.
Therefore X =
Therefore 500 grams of nitrogen will produce grams of ammonia.