# Molecular ionsWatch

#1
How do I do this? I don’t have a clue on what to do??

Thanks.

0
10 months ago
#2
im guessing C, since the others all have oxygen in them and C doesn't
0
#3
(Original post by hello2906)
im guessing C, since the others all have oxygen in them and C doesn't
But how does that explain the answer?
0
10 months ago
#4
(Original post by Yatayyat)
But how does that explain the answer?
It doesn't

By molecular ion - you know in the M/Z graphs they give you where you look at molecular ion peaks? The mass is determined by the largest mass recorded as the ion formed is simply the compound only missing 1 electron

so
A = C4H8O Which has a molecular mass of 72gmol-1
B = C4H7OH = 72gmol-1
C = C5H12 = 72gmol-1
D = C5H10O = 86gmol-1

Each molecule still has the same mass as it's molecular ion too
A simply forms C4H8O+ when an electron is knocked off
1
10 months ago
#5
(Original post by Yatayyat)
But how does that explain the answer?
is the answer C? Because all of the others are a collection of the same Cs and Hs, so will all have precisely the same molecular masses since theyre made up of exactly the same atoms. Oxygen has a slightly different mass to Cs/Hs, so the compound will have a slightly different Mr to the others.
0
#6
(Original post by LiiHyde)
It doesn't

By molecular ion - you know in the M/Z graphs they give you where you look at molecular ion peaks? The mass is determined by the largest mass recorded as the ion formed is simply the compound only missing 1 electron

so
A = C4H8O Which has a molecular mass of 72gmol-1
B = C4H7OH = 72gmol-1
C = C5H12 = 72gmol-1
D = C5H10O = 86gmol-1

Each molecule still has the same mass as it's molecular ion too
A simply forms C4H8O+ when an electron is knocked off
Wait how does D have a mr of 86 isn’t 72?
0
10 months ago
#7
The answer is C, because it is the only one without oxygen. All of the others have the same combination of carbon, hydrogen and oxygen. The precise Mr, i.e. down to six decimal places will be different for different molecular formula, even if the integral value appears the same.
0
#8
(Original post by charco)
The answer is C, because it is the only one without oxygen. All of the others have the same combination of carbon, hydrogen and oxygen. The precise Mr, i.e. down to six decimal places will be different for different molecular formula, even if the integral value appears the same.
Ahh alright. Mr is always the same when it is a whole value but it down to many decimals it’s not exactly the same. Makes sense to me. Thanks man.🙂
0
10 months ago
#9
My mistake I miscounted the carbons in when I drew them out - sorry if I caused any confusion
0
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