In water, Hydrogen is present ________by mass.
Correct answer: B. 11.11%
- A. 22%
- B. 11.11%
- C. 31.13%
- D. 15.15%
Explanation
In 1 mole of water, H2O, the mass of hydrogen is 2 g and the molar mass of water is 18 g, so hydrogen by mass is (2 g / 18 g) x 100 = 11.11%. The likely wrong choice is 22%, which results from using the hydrogen mass fraction incorrectly and effectively doubling the correct percentage.
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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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