Final answer:
To determine the empirical formula for a hydrocarbon with 85.6% carbon, convert the percentage to grams assuming a 100 g sample and then to moles. The smallest whole number ratio of carbon to hydrogen is found to be 1:2, leading to the empirical formula CH2. The correct answer is E. CH₂.
Step-by-step explanation:
To find the empirical formula of a hydrocarbon that is 85.6% carbon by mass, start with a hypothetical 100 g sample of the compound. This approach simplifies the calculation because the mass percentage can directly represent grams.
Thus, we would have 85.6 g of carbon and the remainder (100 g - 85.6 g) as hydrogen, which is 14.4 g. Next, we convert these masses to moles by using the atomic mass unit of carbon (12.01 g/mol) and hydrogen (1.008 g/mol).
For carbon: 85.6 g C × (1 mol C / 12.01 g C) = 7.132 moles of C
For hydrogen: 14.4 g H × (1 mol H / 1.008 g H) = 14.286 moles of H
Then, we divide the moles of each element by the smallest number of moles to find the simplest whole number ratio:
For carbon: 7.132 mol / 7.132 = 1
For hydrogen: 14.286 mol / 7.132 = 2
The smallest whole number ratio of carbon to hydrogen is therefore 1:2, which yields the empirical formula of CH2.
The correct answer is E. CH2.