Answer
molecular formula of acetaldehid is $C_{2}H_{4}O$ .
Work Step by Step
Strategy: 1- Find the empirical formula mass.
2- by dividing molecular mass with empirical formula mass, we can find the number that empirical formula mass must be multiplied to find the molecular formula.
To find the empirical formula mass:
54.5 % C, 9.2 % H, and 36.3 % O. 100 g acetaldehid contains: 54.5 g C, 9.2 g H, and 36.3 g O. These amount converted to moles are:
54.5 g C x $\frac{1 mol (C) }{12g (C)}$= 4.54 mol C
9.2 g H x $\frac{1 mol (H) }{1g (H)}$ = 9.2 mol H
36.3 g O x $\frac{1 mol (O) }{16g (O)}$ = 2.27 mol O
Ignoring the last digit, as experimental error, we now divide with the smallest number of moles, that is 2.2 and we get: 2.0 for C, 4.1 for H, and 1 for O, . So the empirical formula for acetaldehid $C_{2}H_{4}O$.
Mass of empirical formula : 2 x 12 + 4 x 1 + 1 x 16 = 44 amu.
2- We are given the molecular mass of 44 amu, so we can find the number empirical formula mass must be multiplied to find the molecular mass:
n = $\frac{Molecular mass}{empirical (formula-mass)}$
n = $\frac{44}{44}$ = 1
So molecular formula of acetaldehid is $C_{2}H_{4}O$ .
