[bec036]

URGENT

Hey if anyone could help me out if would be greatly appreciated!!   

I have a chem exam coming up soon and im doing some practice questions and was just wondering if anyone knew how to work this out. The question is:

"A hydrocarbon contains 16.3% hydrogen by mass. The empirical formula of the compound is...?" 

I tried to work it out myself but my answer was C₂H₁₂ which is not correct apparently. 

Please show how you worked this out as well (as best you can by typing it)

Thank-you so much 

[UG]

Let's assume you have 100g of the compound. 16.3g of it would be hydrogen and therefore 83.7 grams of it will be carbon. Number of moles of hydrogen in 16.3 grams = 16.3/1 = 16.3 moles
Number of moles of carbon = 83.7/12 = 6.975 moles
So the ratio of hydrogen to carbon is, 16.3 : 6.975 which can be simplified to 2.33 : 1
Make the ratios whole numbers and you'll have your emperical formula 

[bec036]

Let's assume you have 100g of the compound. 16.3g of it would be hydrogen and therefore 83.7 grams of it will be carbon. Number of moles of hydrogen in 16.3 grams = 16.3/1 = 16.3 moles
Number of moles of carbon = 83.7/12 = 6.975 moles
So the ratio of hydrogen to carbon is, 16.3 : 6.975 which can be simplified to 2.33 : 1
Make the ratios whole numbers and you'll have your emperical formula 

THANK-YOU so much!!  would you be able to explain how to make them whole numbers i dont get molecular formulas at all!!  i'm sorry 

[UG]

Multiply the ratio by three so you get, 7 : 3
The answer should be C₃H₇

[bec036]

Multiply the ratio by three so you get, 7 : 3
The answer should be C₃H₇

yes that is the correct answer. how did you know to multiply by 3??

[UG]

2.33 written as a fraction is 7/3. So the ratio is 7/3 : 1
In order to get rid of the three you muiltiply the entire thing by three to get 7 : 3

[bec036]

ah k. i get it!!
thank-you so much 

[UG]

No problemo 
Or should I say, N₂O₄ Pr₂O₆B₃Li₅Mo₈