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## Homework Statement

Really appriciate helps from anyone, these two probs hurt my head

1. Complete combustion of a 4.10g sample containing only propane (C3H5) and pentane (C5H12), yielded 12.42g CO2 and 6.35g H2O. What is the mass % propane in this sample?

a.4.50% b.38.0% c. 50.0% d.80.0% e.30.0%

2. Balance the following equation in basic solution:

Cr^(3+) + O2^(2-) = CrO4^(2-)

the sum of the coefficients is:

a.38 b.27 c.53 d.18 e.49

## Homework Equations

C3H5 + (17/4)O2 = 3CO2 +(5/2)H2O

C5H12 + 8 O2 = 5CO2 + 6H2O

## The Attempt at a Solution

For the first prob, i tried to put x is the mole of C3H5 and y is the mole of C5H12. Then i have sum of their mass equal 4.10g. On other part, i have the moles of CO2 from two equation as the factor of x and y, and then get the sum of them equal 12.42g. I solved the equation systems but get the x is negative? not sure what i did wrong? If anyone know plz tell me, otherwise i think the problem author gave the wrong information.

For the second prob, nothin i can do, i don't know if O2 is reduction or oxidation agent, don't even think O2^(2-) even exists, but my instructor seems pretty sure that equation can be balanced. Very thankful for the help from anyone.