[cemistryspain1]

When completely burning a 65.000 g mixture of propane (C3H8) and heptane (C7H16), 103.867 g of water is produced.

Calculate the percent mass of heptane in the mixture.

Relative atomic masses: H=1.01; C=12.01; O=16.00



thank you!!!!!!

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy.

[cemistryspain1]

The thing is I'm stuck at first level, the balancing part.

I try to balance

C3H8+C7H16 to produce H2O,

but my question is, shouldn't there be on the product's side Carbon to balance it? I don't know how to

[Borek]

You need two separate reaction equations, one for each substance.

Yes, carbon dioxide is produced as well. You will need it to balance reactions, but later it can be safely ignored.

[cemistryspain1]

So I've balanced both reactions separately, but what's the connection between them?

C3H8 + 5 O2 --> 4 H2O + 3 CO2

C7H16 + 11O2 --> 8H2O + 7CO2

Many thanks

[Borek]

Assume you had xg of propane and yg of heptane. Can you express the mass of the mixture and mass of produced water using these variables?

[cemistryspain1]

Well,
I know that

xg + yg = 65.000 g

and I know that the mixture (xg+yg) + oxygen = 103.867 g of water

[Borek]

Use stoichiometry for the second equation. Don't bother about oxygen.

[cemistryspain1]

I don't understand!

Oh well, I give up

[Borek]

xg - how many moles of propane?

1 mole of propane produces 3 moles of water, how many moles will be produced from xg of propane?

[cemistryspain1]

Is this correct:

0.0907x+0.0798y=5.763
x+y=65

x=52.91g
y=12.09g



Many thanks

[Sophia7X]

Is this correct:

0.0907x+0.0798y=5.763
x+y=65

x=52.91g
y=12.09g



Many thanks

That's approximately what I got too.