AP Chemistry 1.3 Elemental Composition of Pure Substances Questions

(ii) For the correct calculated number of moles of H (may be implicit):

$0.1600 \mathrm{~mol} \mathrm{H}_{2} \mathrm{O} \times \frac{2 \mathrm{~mol} \mathrm{H}^{\mathrm{H}}}{1 \mathrm{~mol} \mathrm{H}_{2} \mathrm{O}}=0.3200 \mathrm{~mol} \mathrm{H}$

For the correct empirical formula.

Examples of acceptable responses may include the following:

- x: y: z= (moles of C):(moles of H):(moles of O)

x: y: z=0.2400: 0.3200: 0.2400=3: 4: 3

Therefore, the empirical formula of ascorbic acid is $\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}_{3}$.

- $0.2400 \mathrm{~mol} \mathrm{CO}_{2} \times \frac{1 \mathrm{~mol} \mathrm{C}}{1 \mathrm{~mol} \mathrm{CO}_{2}}=0.2400 \mathrm{~mol} \mathrm{C}$$$\frac{0.3200 \mathrm{~mol} \mathrm{H}}{0.2400 \mathrm{~mol} \mathrm{C}}=\frac{4 \mathrm{H}}{3 \mathrm{C}}$$

Given that the ratio of C:O is 1:1, the empirical formula of ascorbic acid is

$$\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}_{3}.$$