This stupid chemistry question?? HELP?

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Catchmeifyoucan
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#1
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#1
Hydrocarbon "A" contains 87.8% carbon and 12.2% hydrogen by mass. It's relative molecular mass is 82. "A" decolourises bromine water.

"A" reacts with hydrogen, in the presence of a nickel catalyst, to form "B" 0.1G of "A"was found to absorb 27.3cm3 of hydrogen (at s.t.p) "B" does not decolourise bromine water.

A) determine the molecular formula of "A"
I got this to be C2H4 is this correct?

B) How many moles of A react with hydrogen ?

C) How many moles of hydrogen react?

D) How many moles of hydrogen react with one mole of "A" ?

E) How many double bonds does "A" have in it's molecule?

F) What is the molecular formula of "B" ?
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EierVonSatan
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#2
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A) no - the mass of your molecule is 28, it needs to be 82.

Divide the %mass by the atomic masses of each element, what do you get?
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Catchmeifyoucan
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#3
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#3
(Original post by EierVonSatan)
A) no - the mass of your molecule is 28, it needs to be 82.

Divide the %mass by the atomic masses of each element, what do you get?
I did.
C H
87.8/12 12.2/1
=7.3167 =12.2 (divide by the lowest value)
=7.3167/7.3167 =12.2/7.3167
=1 =1.6
Therefore CH2?
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EierVonSatan
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#4
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(Original post by Catchmeifyoucan)
I did.
C H
87.8/12 12.2/1
=7.3167 =12.2 (divide by the lowest value)
=7.3167/7.3167 =12.2/7.3167
=1 =1.6
Therefore CH2?
not quite no, multiply both by 3 so should get:

C3H5 which is the empirical formula, you need the molecular one
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Catchmeifyoucan
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#5
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(Original post by EierVonSatan)
not quite no, multiply both by 3 so should get:

C3H5 which is the empirical formula, you need the molecular one
Oh I see...so M.F will be C6H10
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EierVonSatan
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#6
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#6
(Original post by Catchmeifyoucan)
Oh I see...so M.F will be C6H10
exactly

B) now knowing the mass and formula, how many moles of A reacted?
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LimeTree.
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#7
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(Original post by Catchmeifyoucan)
Oh I see...so M.F will be C6H10
Bingo ;P
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Catchmeifyoucan
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#8
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#8
(Original post by EierVonSatan)
exactly

B) now knowing the mass and formula, how many moles of A reacted?
is it going to be 0.1/82 =0.001219512?
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EierVonSatan
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#9
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#9
(Original post by Catchmeifyoucan)
is it going to be 0.1/82 =0.001219512?
Yep

C) 1 mol of H2 occupies 22.4 dm3, so how many moles of H2 are consumed?
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Catchmeifyoucan
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#10
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(Original post by EierVonSatan)
Yep

C) 1 mol of H2 occupies 22.4 dm3, so how many moles of H2 are consumed?
I'm not sure do you use the formula V= m/24dm3


so it will be 0.0273 x 24dm3=0.6552?
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EierVonSatan
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#11
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#11
(Original post by Catchmeifyoucan)
I'm not sure do you use the formula V= m/24dm3


so it will be 0.0273 x 24dm3=0.6552?
You need to divide instead (by 22.4)
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Catchmeifyoucan
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#12
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(Original post by EierVonSatan)
You need to divide instead (by 22.4)
so will it be 0.0273 x 22.4 =0.61152 moles?
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EierVonSatan
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#13
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#13
(Original post by Catchmeifyoucan)
so will it be 0.0273 x 22.4 =0.61152 moles?
No, divide :p:

0.0121875...
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Catchmeifyoucan
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#14
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#14
Ohh okay I get it now, and will D) be 1:1 ratio?
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EierVonSatan
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#15
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#15
(Original post by Catchmeifyoucan)
Ohh okay I get it now, and will D) be 1:1 ratio?
Yes :yep:
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Catchmeifyoucan
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#16
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#16
(Original post by EierVonSatan)
Yes :yep:
So for E) "A" will have 2 double bonds if it is C6H10?
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EierVonSatan
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#17
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#17
(Original post by Catchmeifyoucan)
So for E) "A" will have 2 double bonds if it is C6H10?
Nah, you've only added one mole of H2 - so one double bond.
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Catchmeifyoucan
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#18
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#18
(Original post by EierVonSatan)
Nah, you've only added one mole of H2 - so one double bond.
Oh..but if you put one double bond
in C6H10 there's 11 hydrogens?
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EierVonSatan
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#19
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#19
(Original post by Catchmeifyoucan)
Oh..but if you put one double bond
in C6H10 there's 11 hydrogens?
hint: what is the formula of cyclohexane?
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Catchmeifyoucan
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#20
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#20
(Original post by EierVonSatan)
hint: what is the formula of cyclohexane?
C6H12 is that "B"
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