Mole Concept

Easychemistry

A hydrocarbon sample contains 75% carbon by mass and remainder hydrogen. Its empirical formula is (Atomic masses: C=12, H=1)

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CH2

C3H8

CH4

C2H6

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Subject: chemistry
Chapter: some basic concepts in chemistry
Topic: mole concept
Difficulty: Easy
Year: 2025

Solution

Correct Answer:

CH4

Define Mass Percentages:
- Carbon ( $C$ ) = $75%$
- Hydrogen ( $H$ ) = $100% - 75% = 25%$ .
Convert to Moles (assume 100g sample):
- $M o l es o f C = \frac{75 g}{12 g / m o l} = 6.25 m o l$ .
- $M o l es o f H = \frac{25 g}{1 g / m o l} = 25 m o l$ .
Determine Atomic Ratio:
- $R a t i o (H : C) = \frac{25}{6.25} = 4$ .
Formulate Empirical Formula:
- Since the ratio is $1 : 4$ , the empirical formula is $C H_{4}$ .

This easy difficulty chemistry question is from the chapter some basic concepts in chemistry, covering the topic of mole concept. It appeared in the 2025 exam.

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