Question

what is the empirical formula of a compound with 20% hydrogen and 80% carbon?
a. h₂c
b. ch₄
c. h₂c₄
d. h₃c₂

Explanation:

Step1: Assume 100g of the compound

Since the compound has 20% hydrogen and 80% carbon by mass, if we assume 100g of the compound, there are 20g of hydrogen and 80g of carbon.

Step2: Calculate the number of moles

The molar mass of \(H\) is \(1g/mol\) and the molar mass of \(C\) is \(12g/mol\).
The number of moles of \(H\), \(n_{H}=\frac{20g}{1g/mol} = 20mol\)
The number of moles of \(C\), \(n_{C}=\frac{80g}{12g/mol}=\frac{20}{3}mol\)

Step3: Find the mole - ratio

Divide the number of moles of each element by the smallest number of moles.
\(n_{C}:n_{H}=\frac{20}{3}:20 = 1:3\)

Answer:

A. \(H_{2}C\)