MASS TO MASS STOICHIOMETRY

MOLE-MASS PROBLEMSProblem 1:

1.50 mol of KClO3 decomposes. How many grams of O2 will be produced?

[k = 39, Cl = 35.5, O = 16]

2 KClO3 2 KCl + 3 O2

THREE STEPS…GET YOUR CORRECT ANSWER

Use your mole ratio equationGet the answer in moles and thenConvert to Mass.

Next:

If you are given a mass in the problem, you will need to convert this to moles first

LET’S GO!2 KClO3 2 KCl + 3 O2

Convert to mass

2.25 mol x 32.0 g/mol = 72.0 grams

TRY THIS:

We want to produce 2.75 mol of KCl. How many grams of KClO3 would be required?

MASS TO MASS

We can use a simple 3 step method to solve stoichiometric questions with balanced equations. Identify the given and convert it to moles. Identify the unknown, and multiply the given number of moles

by the mole ratio to produce moles of desired substance.Convert moles of desired substance to the units asked for in

the question.

EXAMPLE

What mass of methane gas in grams must burn to produce 365 grams of water, by the following chemical reactions ?

Given is 365 g of water. Calculate moles of water.

Identify desired; mass of Methane gas. Multiple by mole ratio

_1_CH4(g) + _2_O2(g) _2_H2O (g) + _1_CO2(g)

365 g ÷18.02 g/mol = 20.25 mol

20.25 mol H2O (l) X 1 CH4 (g) = 10.13 mol CO2 (g)

    2 H2O (g)    

Convert moles of desired to the units asked for in the question: Mass of Methane gas. 

Assignment: Mass to Mass Stoichiometry

10.13 mol CO2 X 44.01 g/mol = 446 g