1. Mass to Mass Conversions
Ch 9 Stoichiometry
Mass to Mass Conversions

2. Mass-Mass Conversions
A mass to mass conversion is a three step process involving:
Converting the known to moles
Using the mole ratio to convert known to unknown
Converting the unknown to mass

3. Combustion Example 1CH4 + 2O2 → 2H20 + 1CO2
10.0 grams of methane combusts producing carbon dioxide gas and water vapor. How much oxygen is required to fully combust the grams of methane?
Write and balance the equation
1CH4 + 2O2 → 2H20 + 1CO2

4. Step 1 grams to moles
In converting from grams to moles you divide by the molar mass of the known.
Actually you multiply by the ratio of one mole to x number of grams.

5. Step 2 moles to moles
In converting from moles to moles you use a ratio from the balanced equation.
The unknown should be in the numerator and the known in the denominator.

6. Step 3 moles to grams
The final step is to convert the moles of unknown to grams.
To do this multiply the moles by the molar mass of the unknown.

7. Steps 1-3 together
The better method is to do all three steps in one calculation and one equation line.