Chemistry Stoichiometry

Question

If 200.8 g of carbon dioxide gas is made from the complete combustion of isopropanol (C₃H₇OH), how many moles of oxygen are used up?

Answer 1

Hello, Hannah,

Please add whatever information you already have when posting questions involving stoichiometry. It isn't clear which part of the problem you'd like help on. For example:

1. Were you able to form a balanced equation?
2. Have you calculated the molar masses for each compound?
3. Are there questions related to how one calculates moles?

I get the following balanced equation:

We are given the mass of CO₂ and asked how many moles of isopropanol are consumed to produce that amount of CO₂. The balanced equation says that we produce 3 moles of CO₂ for every 1 mole of C₃H₇OH.

We can use that information as a conversion factor:

(3 moles CO₂)/(1 mole C₃H₇OH)

We can invert that to: (1 mole C₃H₇OH)/ (3 moles CO₂)

If we know the moles of CO₂ we can find the moles of C₃H₇OH.

200.8 grams of CO₂

The molar mass of CO₂ is 44.0g/mole

Moles CO₂ = (200.8 g)/(44.0 g/mole) = 4.563 moles CO₂ (4 sig figs)

Use the conversion factor:

4.563 moles CO₂ * (1 mole C₃H₇OH)/ (3 moles CO₂) = 13.69 moles C₃H₇OH

Note how the units cancel to give the answer sought.

Bob