c11223
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Q) In a molecule of a hydrocarbon, the fraction by mass of carbon is 9/11
What is the empirical formula of the hydrocarbon?

a) CH
b) CH3
c) C3H8
d) C5H12

Please help me I got CH2 but the correct answer is C.
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BobbJo
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(Original post by c11223)
Q) In a molecule of a hydrocarbon, the fraction by mass of carbon is 9/11
What is the empirical formula of the hydrocarbon?

a) CH
b) CH3
c) C3H8
d) C5H12

Please help me I got CH2 but the correct answer is C.
C ; H = 9/(11x12):2/(11x1) = 3/44 : 2/11 = 3 : 8 so C.

dividing 9/11 by 12 because relative atomic mass of carbon is 12
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c11223
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I got 3/44 and 2/1,1
but afterwards don't you have to divide by the smallest number to find the ratio?
Last edited by c11223; 1 year ago
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BobbJo
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(Original post by c11223)
(Original post by BobbJo)C ; H = 9/(11x12):2/(11x1) = 3/44 : 2/11 = 3 : 8 so C.

dividing 9/11 by 12 because relative atomic mass of carbon is 12
but don't you have to divide by the smallest number to find the ratio?
find the mole ratio first by dividing by rel atomic masses
then i divided by 1/44
Last edited by BobbJo; 1 year ago
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c11223
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I got 3/44 and 2/1,1

but afterwards don't you have to divide by the smallest number to find the ratio?
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BobbJo
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(Original post by c11223)
I got 3/44 and 2/1,1

but afterwards don't you have to divide by the smallest number to find the ratio?
divide by smallest number which is 3/44 or just divide by 1/44 because it's easier

convert to percentages if it helps you understand more
Last edited by BobbJo; 1 year ago
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c11223
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(Original post by BobbJo)
divide by smallest number which is 3/44 or just divide by 1/44 because it's easier

convert to percentages if it helps you understand more
i thought 3/44 was the smallest number?
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BobbJo
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(Original post by c11223)
i thought 3/44 was the smallest number?
yes
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c11223
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(Original post by BobbJo)
yes
sorry i'm a bit confused why would i divide by 1/44 if 3/44 is the smallest?
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BobbJo
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(Original post by c11223)
sorry i'm a bit confused why would i divide by 1/44 if 3/44 is the smallest?
do whatever method you want

C;H = 3/44 : 2/11
divide by 3/44
C;H = 1 : 8/3
C;H = 3:8
same answer
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c11223
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#11
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(Original post by BobbJo)
do whatever method you want

C;H = 3/44 : 2/11
divide by 3/44
C;H = 1 : 8/3
C;H = 3:8
same answer
But i'm still getting CH2
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BobbJo
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(Original post by c11223)
But i'm still getting CH2
You did it wrong. I showed how to do it in post 10. Post your working or look at post 10.
2/11 divided by 3/44 is 8/3
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c11223
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(Original post by BobbJo)
You did it wrong. I showed how to do it in post 10. Post your working or look at post 10.
2/11 divided by 3/44 is 8/3
Moles of C = 9/(11x12)=3/44
Moles of H = 2/(11x1)=2/11
3/44 / 3/44 =1
2/11 / 3/44 =2.6 (not sure if i should round to 3)
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BobbJo
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#14
(Original post by c11223)
Moles of C = 9/(11x12)=3/44
Moles of H = 2/(11x1)=2/11
3/44 / 3/44 =1
2/11 / 3/44 =2.6 (not sure if i should round to 3)
im not sure why you ignore post 10

2/11 divided by 3/44 = 8/3
you multiply by 3 and get the correct ratio
don't round 8/3 to 3
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c11223
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(Original post by BobbJo)
im not sure why you ignore post 10

2/11 divided by 3/44 = 8/3
you multiply by 3 and get the correct ratio
don't round 8/3 to 3
Ohh i understand now thanks!
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