How many molecules are present in 0.20 g of Hydrogen gas? Select the correct option.
Correct answer: A. 0.20 x 3.01 x 10^23
- A. 0.20 x 3.01 x 10^23
- B. 0.20 x 2.016
- C. 0.70 x 6.02 x 10^23
- D. 1.008 x 6.02 x 10^23
Explanation
To find the number of molecules in 0.20 g of hydrogen gas, first recognize that hydrogen gas (H2) is diatomic. This means that 1 mole of hydrogen gas, which weighs 2.016 g, contains 6.02 x 1023 molecules. Therefore, 1 g of hydrogen gas contains 3.01 x 1023 molecules. To find the number of molecules in 0.20 g, multiply 0.20 by 3.01 x 1023, yielding 0.20 x 3.01 x 1023 molecules.Option A correctly uses this method. Option B fails by using the molar mass without Avogadro's number, Option C uses an incorrect proportion, and Option D uses the atomic mass of hydrogen instead of the diatomic gas.
This question appeared on the ETEA MDCAT 2013 paper, which you can sit online with every answer explained.
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About Moles and Avogadro's Number
The mole connects the microscopic number of particles with measurable mass, using Avogadro's number, 6.022 × 10²³ particles per mole. Questions involve molar mass, conversion between mass, moles and particles, percentage composition, empirical and molecular formulas, and distinguishing atoms, molecules, ions and formula units.
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