[LHM]

An organic molecule of four carbons is shown to be 55.1% carbon, 0.40% hydrogen, and 18.4% oxygen by mass. Which of the following functional groups is NOT present in this compound?

A) alcohol
B) carboxylic acid
C) amide
D) alkene
E) ketone

So I assumed that there's 100 g of the compound, which means 55.1 g of C, 0.40 g of H, and 18.4 g of O. However, it seems odd to me that there's four carbons, because then there isn't any atom of hydrogen at all? 55.1 g = 4.59 mol C, 0.40 g = 0.397 mol H, and 18.4 g = 1.15 mol O. So how do you know which functional group isn't present?

[opti384]

I think assuming the mass as 100g is not right because you know that the mass of carbon in 1mol of the compound is 48g (the molecule has four carbons).

[Hybrid]

i feel there is something wrong in this question, and the odd to me that if cpd containing N "remaining of 100%" CHN give % of C H N and then we substract to get O.
where did you get this question??

But it may contain other elements (halogens , sulfur) , it is not the full elemntal analyss result the one here, and he just want you to exclude gps 
so i will exclude COOH "H, and high O" , -OH , CONH "amide also has H and N"

N.B. 0.4% is allowable deviation in CHN so there may be no H at all

[Borek]

There is no way four carbons molecule can contain 55.1:0.4 carbon:hydrogen mass ratio. Assuming just one hydrogen mass ratio would be 48:1. So there is either no hydrogen, or no four carbons.

I guess it is a typo, and it should read 10.4% hydrogen. That will yield a nice empirical formula.