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Acetaldehyde contains C, H and O in the mass ratio of 6:1:4. Its mass spectrum shows its molecular mass to be 44 amu. what is the molecular formula?

2007-09-20 19:24:45 · 3 answers · asked by Anonymous in Science & Mathematics Chemistry

3 answers

so u have 11 parts. 6+1+4=11.
C = 6/11 parts = 54%
H = 1/11 parts = 9.01%
O = 4/11 parts = 36.4%

iuno how this works, but it does ><.
C= 12 amu/mole. so: 54%/12amu = 4.55 in ratio
H= 1 amu/mole so: 9.01%/1amu = 9.01 in ratio
O = 16amu/mole so: 36.4%/16amu = 2.27 in ratio

simplify the ratios:
C=4.55/2.27 = 2
H=9.01/2.27 = 4
O=2.27/2.27 = 1
so the emperical and in this case, molecular formula as well of acetaldehyde is C2H4O1=your answer
16(2)+1(4)+16(1)=44!
sorry if its unclear ><. explaining would take forever

2007-09-20 19:53:05 · answer #1 · answered by bobrowra 2 · 2 0

Assume the formula is CaHbOc

Then clearly 12a + b + 16c = 44 ..... Eqn 1

(using integral AW and summing to get the MW)

Given that C:H:O is 6:1:4 then 12a/b = 6 or 2a=b and 16c/b = 4 or 4c = b

Substituting into Eqn 1 gives 12 x b/2 + b + 16 x b/4 =44 or 6b+ b + 4b = 44 or b= 4. Thus a = 2 and c=1.

Hence acetaldehyde is C2H4O or CH3CHO

2007-09-20 19:56:31 · answer #2 · answered by A S 4 · 1 0

Take 16 off the amu for the O atom, leaving 28. This must therefore have 2 x C (= 24) and 4 x H (= 4).

Ethanal.

Or you could do a proper empirical formula calculation.

2007-09-20 19:56:06 · answer #3 · answered by Gervald F 7 · 1 0

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