The mass of 0.5 mole of sodium hydroxide, NaOH, is
Correct answer: B. 20 g
- A. 40 g
- B. 20 g
- C. 80 g
- D. 10 g
Explanation
The molar mass is 23 + 16 + 1, that is 40 g per mole, so half a mole has a mass of 20 g. Mass is calculated as number of moles multiplied by molar mass, and the commonest error is to quote the molar mass itself without applying the 0.5. This is the calculation behind preparing a standard solution in the laboratory.
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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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