Question

The weight percentage of C and H in a hydrocarbon is in the ratio of 4:1. What is its empirical formula?

• A. CH
• B. CH\( _2 \)
• C. CH\( _3 \)
• D. CH\( _4 \)

Hint:

To determine the empirical formula from weight percentages, follow these steps: 1. Assume a 100g sample so that the weight percentages become the masses in grams. 2. Convert the mass of each element to moles by dividing by its atomic weight. 3. Find the simplest whole number ratio of the moles of the elements. This ratio gives the subscripts in the empirical formula.

Answer 1

The Correct Option is C

Let the weight percentage of Carbon (C) be 4x and the weight percentage of Hydrogen (H) be 1x.
To find the empirical formula, we need to determine the mole ratio of C and H.
We can do this by dividing the weight percentage of each element by its atomic weight and then finding the simplest whole number ratio.
Atomic weight of Carbon (C) = 12 amu Atomic weight of Hydrogen (H) = 1 amu Number of moles of C \( \propto \frac{\text{weight percentage of C}}{\text{atomic weight of C}} = \frac{4x}{12} = \frac{x}{3} \) Number of moles of H \( \propto \frac{\text{weight percentage of H}}{\text{atomic weight of H}} = \frac{1x}{1} = x \) Now, we need to find the simplest whole number ratio of the moles of C to the moles of H: Ratio C : H = \( \frac{x}{3} : x \) To get a whole number ratio, we can divide both sides by the smallest fraction, which is \( \frac{x}{3} \): Ratio C : H = \( \frac{x/3}{x/3} : \frac{x}{x/3} = 1 : 3 \) So, the mole ratio of Carbon to Hydrogen is 1:3.
Therefore, the empirical formula of the hydrocarbon is CH\( _3 \).