Percentage yeild of CO2...HELP NEEDED?

Question

Octane is the representative compund in petrol. The equation for its combustion is given below.

2C8H18 + 25O2------>16CO2 + 18H2O

When 702 grams (1.0 L) of octane burnt 1.4 kg of carbon dioxide obtained. What is the percentage yeild of CO2??

Answer 1

first convert gms of octane to moles

702 gms x 1 mol/114.2 gms= 6.15 moles

next convert gms of CO2 to moles

1400gms x 1 mol/44gms= 31.8 moles

you know that 2 moles of octane give 16 moles of CO2

Theoretical yield of CO2= 16/2=x/6.15

x= 49.2

actual yield= 31.8

% yield= 31.8/49.2 x 100= 64.6%

Answer 2

LOL!

really, it's 75.2%.