The mass of 0.5 mole of sodium hydroxide, NaOH, is
- 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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