[pre med UK]

Hi people, i cant get my head around this question
exp 1: 10.00g of substance X is burned completely in oxygen, producing 24.45g of carbon dioxide amd 10.00 of water. No other compounds are detected, so you are happy that substance X is composed of only hydrogen, oxygen and carbon!

From this experiment , what is the empericial formula of substance X??   
Any help would be appreciated!
Thanks

[enahs]

How many moles of CO₂ and H₂O was produced? How many moles of C, H and O does that make? What is the ratio of C, H and O to each other?

[pre med UK]

it doesnt state in the question how many moles were produced, just the amounts stated i.e. the masses

[enahs]

If you have the mass of known substances you know the moles from the molecular weight.

I.E. in 24.45g of CO2, how many moles are there?

[pre med UK]

well  i guess that would be for [CO][/2]
24.25 / (44) = 0.55
so now i have the number of moles for each product, what do i do next ?

[enahs]

How many moles of water are there?

In 0.55 moles of CO2, how many moles are there of oxygen and how many moles are there of carbon? What about water, how many moles of hydrogen and how many moles of oxygen?

[pre med UK]

In the 0.55 moles of CO2 (24.45 / 44)
no of moles of Carbon  in CO2 =
  24.45 x (12/44) = 6.6
no moles of oxygen in CO2 =
  24.45 x (16/44) = 8.8

number of H20 mioles =
10g / (18) = 0.55
no of moles of H in H20 =
10 x (2/18 ) = 1.1
 no of mole of Oxygen in H20 =
10 x (16/18) = 8.8

I'm just wondering what to do next, i have the answer to this question but i want to and need to understand how to arrive at the answer which is C4H8O
Please can you help me more! Thanks for the help so far!

[rannekk]

Greetings masters of chemistry!
I could use some help with this question:
3.40g of CaSO4 (M=136g mol-1) is formed when 4.30g of hydrated calcium sulfate is heated to constant mass. How many moles of water of crystallisation are combined with each mole of calcium sulfate?

A: 1
B: 2
C: 3
D: 4

.. If you can help me by showing the working out i would be truly gratefull as i have been extremely frustrated by this question.

Cheers

[DrCMS]

You've got moles and grams all confused.

10.00g of your unknown burn to give:

24.45g of carbon dioxide and 10.00g of water

24.45g of CO₂ contains 6.67g of carbon (24.45*12/44 = 6.67)
10.00g of H₂O contains 1.11g of hydrogen (10.00*2*1/18 = 1.11)

The orginal substance weighed 10.00g and you're told only contained Carbon Hydrogen and Oxygen.
6.6g was Carbon
1.1g was Hydrogen
so
2.22g must have been Oxygen (10.00-6.67-1.11=2.22)

6.67g Carbon we know is 0.55moles
1.11g Hydrogen we know is 1.11moles
2.22g Oxygen is 0.14 moles (2.22/16 = 0.14)

That gives an empirical formula of
C_0.55H_1.11O_0.14

If you multiply everything up to get oxygen as 1 you get
C_3.93H_7.93O₁

Which rounded to whole numbers is
C₄H₈O

[pre med UK]

thank you so much i'm glad you clarified my moments of stupidity x