Question

Analysis of a sample of an organic compound showed it to contain 39.9% carbon 6.9% hydrogen and 53.3% oxygen

Answer 1

There is no question itself, but this data is likely given to determine the empirical formula of the compound.

100 grams of this compound contain 39.9 g (C), 6.9 g (H) and 53.3 g (O).

Amounts of each element in moles are:

$n(C)=\frac{39.9g}{12.01g/mol}=3.32mol$

$n(H)=\frac{6.9g}{1.01g/mol}=6.8mol$

$n(O)=\frac{53.3g}{16.0g/mol}=3.33mol$

The C : H : O molar ratio appears to be 1 : 2 : 1, hence the empirical formula is CH₂O.

The molecular formula cannot be determined without knowing the molar mass of the compound.