Question 3.15: CALCULATING AN EMPIRICAL FORMULA FROM A PERCENT COMPOSITION ...
CALCULATING AN EMPIRICAL FORMULA FROM A PERCENT COMPOSITION
Vitamin C (ascorbic acid) contains 40.92% C, 4.58% H, and 54.50% O by mass. What is the empirical formula of ascorbic acid?
STRATEGY
Assume that you have 100.00 g of ascorbic acid, and then carry out the procedure outlined in Figure 3.7.
First, find the number of moles of each element in the sample:
40.92 \cancel{g C} × \frac{1 mol C}{12.0 \cancel{g C}} = 3.41 mol C
4.58 \cancel{g H} × \frac{1 mol H}{1.01 \cancel{g H}} = 4.53 mol H
54.50 \cancel{g O} × \frac{1 mol O}{16.0 \cancel{g O}} = 3.41 mol O
Dividing each of the three numbers by the smallest (3.41 mol) gives a C:H:O mole ratio of 1 :1.33 :1 and a temporary formula of C_{1}H_{1.33}O_{1}. Multiplying the subscripts by small integers in a trial-and-error procedure until whole numbers are found then gives the empirical formula: C_{(3×1)}H_{(3×1.33)}O_{(3×1)} = C_{3}H_{4}O_{3}.