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Class 9 Chemistry · Chapter 4 · Test 9

Percentage Composition Problems

25 MCQs covering molar mass calculations, mass relationships in chemical reactions, percentage composition of compounds,

MCQs

25 questions · 20 min · 25 marks

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Sample questions

The first 5 of 25. Try each one, then tap to see the answer.

  1. Question 1

    What is the molar mass of water H2O?

    • A16 g/mol
    • B18 g/mol
    • C20 g/mol
    • D22 g/mol
    Show answer

    Answer: B

    Water has two hydrogen atoms and one oxygen atom giving a molar mass of 18 g/mol.

  2. Question 2

    What is the molar mass of carbon dioxide CO2?

    • A28 g/mol
    • B32 g/mol
    • C40 g/mol
    • D44 g/mol
    Show answer

    Answer: D

    Carbon dioxide has one carbon atom and two oxygen atoms giving a molar mass of 44 g/mol.

  3. Question 3

    What is the approximate percentage of oxygen by mass in water H2O?

    • A11.1 percent
    • B88.9 percent
    • C50 percent
    • D66.7 percent
    Show answer

    Answer: B

    Water has 16 g of oxygen in 18 g of water so the percentage is about 88.9 percent.

  4. Question 4

    What is the approximate percentage of hydrogen by mass in water H2O?

    • A11.1 percent
    • B22.2 percent
    • C50 percent
    • D88.9 percent
    Show answer

    Answer: A

    Water contains 2 g of hydrogen in 18 g of water so the percentage is about 11.1 percent.

  5. Question 5

    What is the mass of 2 moles of carbon atoms?

    • A12 g
    • B24 g
    • C36 g
    • D48 g
    Show answer

    Answer: B

    The molar mass of carbon is 12 g/mol so 2 moles have a mass of 24 g.

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