JAMB Chemistry 2023 Paper

Concept:Molar mass is the total mass of one mole of a compound, found by adding the molar masses of all atoms present.Explanation:Water has the chemical formula $\mathrm{H}_2\mathrm{O}$.It contains 2 hydrogen atoms and 1 oxygen atom.Molar mass of hydrogen $= 1\ \mathrm{g/mol}$.Molar mass of oxygen $= 16\ \mathrm{g/mol}$.Add the contributions: $(2 \times 1\ \mathrm{g/mol}) + (1 \times 16\ \mathrm{g/mol}) = 2\ \mathrm{g/mol} + 16\ \mathrm{g/mol} = 18\ \mathrm{g/mol}$.Thus, one mole of water weighs $18\ \mathrm{g}$.Answer:The molar mass of water is $18\ \mathrm{g/mol}$, so the correct option is A.