Question

A compound has been shown to contain 14.5 percent hydrogen and 85.5 percent carbon by mass.

Answer 1

Answer:

• Option d. Its empirical formula is CH₂.

Explanation:

The percent composition of the compound allow you to calculate the empirical formula of the compound but is not enough to calculate either the molar mass or the molecular formula. So, since now you can discard options b. and c.

Telling that it is a hydrocarbon (option e.) is true but very vague compared with finding the empirical formula. So, you can also discard the option e.

The fact that the product has a triple bond cannot be concluded from the percent composition, you should find the molecular formula to assert whether it contains or not a triple bond. So, you could discard option a., which lets you only with choice d.

Let us find the empirical formula to be certain that it is CH₂.

1.  First, assume a basis of 100 g of compound:

• H: 14.5% × 100 g = 14.0 g

• C: 85.5% × 100 g = 85.5 g

2. Divide each element by its atomic mass to find number of moles:

• H: 14.0 g / 1.008 g/mol = 14.38 mol

• C: 85.5 g / 12.011 g/mol = 7.12 mol

3. Divide both amounts by the smallest number, to find the mole ratio:

• H: 14.38 mol / 7.12 mol ≈ 2
• C: 7.12 mol / 7.12 mol = 1.

Hence, the ratio is 2:1 and the empirical formula is CH₂.