[steph_xox]

25g of a hydrocarbon undergoes complete combustion leading to the formation of 77 g of CO2. What is the % of carbon in the hydrocarbon?

so far i have set out a combustion equation

CxHy + O2 ----> Co2 + H2O

the number of mol of Co2 can be figured out using mass/molar mass formula to equal 1.75 mol of CO2
then i assume i use the 1:1 ratio?

[opti384]

I think you won't need to do that. As you can see from the equation, all of the carbon in the carbon dioxide is from the hydrocarbon.

[steph_xox]

yeah i get that , but how do i find the %?

[opti384]

Okay then what are the grams of carbon in the hydrocarbon?

[steph_xox]

grams = mol x mr

1.75 x 12?

[opti384]

Yes. So among 25g of the hydrocarbon, 21g is the carbon right?

Now you can find the % of carbon inside the hydrocarbon.

[steph_xox]

thankyou