If air is 20% oxygen, and the reaction is

Question

2C2H2 + 5O2 --> 4CO2 + 2H2O,

What volume of oxygen would be needed to completely burn 1.00 L of acetylene (C2H2)?
I got 2.50 L but I'm not sure it's right.

What volume of air would be needed to completely burn 1.00 L of acetylene gas?
I got 3.00 L.

What volume of air would be needed to burn 1.00 L of vaporized octane?
The reaction is:
2C8H18 + 25O2 --> 16CO2 + 18H2O
I got 15.0 L.

Answer 1

2.5L is right for a.
I don't agree with 3.00 L for b. What you want is ?Lair x 0.2 oxygen = 2.5 L oxygen.
?Lair = 2.5 Loxygen/0.2 oxygen = ? which I think is 12.5 L air. Check it.
12.5 L air x 0.2 oxygen = 2.5 L oxygen.

Do c the same way.

Answer 2

I'm not exactly sure how you do the first step.
Are you using the 2.5 L from a?

So would the answer to c be 62.5 L?
? L O2 = 1.00 L x 1 mol/22.4 L x 25 mol O2/2 mol C8H18 x 22.4 L/1 mol O2
= 12.5 L O2

?L air = 12.5 L (5)
=62.5 L air

Answer 3

okay thank you!
12.5 is correct