# Empiric formula question

a matirial which weighs 1.235gram
made of carbon oxigen and hydrogen
and this material burned in oxigen
which gives 3.425 gram of CO_2
and 0.971 of H_2O ??
what is the ampiric formula of the material
??

Borek
Mentor
1258 posts and you still don't know that you have to try by yourself before asking for help?

tiny-tim
Homework Helper
a matirial which weighs 1.235gram
made of carbon oxigen and hydrogen
and this material burned in oxigen
which gives 3.425 gram of CO_2
and 0.971 of H_2O ??
what is the ampiric formula of the material
??

Hi transgalactic!

What equations do you think are involved, and what constants do you need to know?

symbolipoint
Homework Helper
Gold Member
This one was reasonably difficult, but I found an answer. The trick is to account for both moles formula balance AND mass balance. (Or I should say, atoms balance AND mass balance). Initially, you have variables for the subscripts in the unknown C-H-O compound, and the way I proceeded, a coefficient variable for the reactant oxygen molecule and a coefficient 1 for the unknown compound. Like I say, I came up with what I believe is a very reasonable empirical formula result. I'd like to plainly state the result here, now, but doing so might not be acceptable at this state of progress on the forum.

i have 0.077824106 moles of CO_2
and 0.05389869 moles of H_2O

what to do next??

it not a whole numbers
and i dont know how to build balancing equations for this
??

symbolipoint
Homework Helper
Gold Member
Well, so you have been thinking about and studying this exercise some more. Good.

i have 0.077824106 moles of CO_2
and 0.05389869 moles of H_2O

One of those values looks familar; the other I do not remember. I solved the problem on my own several days ago.

what to do next??

See my last post on this topic. At first, you do not yet know the actual coefficients for the reactant compounds.

it not a whole numbers
and i dont know how to build balancing equations for this
??
The coefficients are unknow to start with, just as the subscripts for the atoms in the unknown compound. You need basic algebra-arithmetic skills. The decision on which final WHOLE numbers to find will come as one of your last steps. I initially found nonwhole values for one or more subscripts in the atoms of the compound also. The process was finished by finding a whole number factor which would keep all subscripts as extremely close to whole OR whole; and just good judgement.

ok
i have to find coefficient for C O H
C=x
O=y
H=z
x+0=0.077824106
y+2=2*0.077824106+0.05389869
z+0=2*0.05389869

how to get whole cofficients from this decimal numbers
??

hint:

can you calculate the number of moles of CO2 you obtain?! If the products are CO2 and H2O only, then all the Carbon from the initial material have gone into CO2.

so, if you have x mol of CO2 formed, then you should have had x mol of Carbon in the initial substance.

Using this same logic you can find out for Hydrogen.

but for Oxygen it is going to be a little bit tricky since the oxygen in the product comes from both the initial material and the oxygen gas supplied. you have find an alternative path!