How many grams of CO2 are produced by the combustion of 289 g of a mixture that is 28.6% CH4 and 71.4% C3H8 by mass?

Explanation:

You have two combustion reactions — one of methane and one of propane.

For each component, we must calculate the mass, then do the conversions

mass of X ⟶ moles of X ⟶ moles of CO₂

Then, we can find the total moles of CO₂ and convert to grams.

1. Mass of each component

(a) Methane

(b) Propane

2. CO₂ from methane

We will need a chemical equation with masses and molar masses, so, let's gather all the information in one place.

Mᵣ:       16.04               44.01

            CH₄ + 2O₂ ⟶ CO₂ +2H₂O

m/g:    82.65

You start with the substance for which they give you numbers.

For example, this question gives you the masses of CH₄ and C₃H₈ and asks you to find the total mass of CO₂.  

(a) Moles of CH₄

(b) Moles of CO₂

3. CO₂ from propane

Mᵣ:       44.10                44.01

           C₃H₈ + 5O₂ ⟶ 3CO₂ +4H₂O

m/g:    206.3

(a) Moles of C₃H₈

(b) Moles of CO₂

4. Mass of CO₂

(a) Total moles of CO₂

Total moles = 5.153 + 14.04 = 19.19 mol CO₂

(b) Mass of CO₂