Compounds of the alkali metals
2 marks · EasyA student dissolves 5.1 g of sodium chloride in water. Sodium chloride is a typical Group 1 metal compound. (Relative atomic masses: Na = 23, Cl = 35.5)
Calculate the number of moles of sodium chloride dissolved.
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0.087 mol (±0.002)
Also accept: 0.0868 mol
Common mistakes: Incorrect molar mass calculation for NaCl
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Marking points
M1 · 1 mark · Calculates the molar mass of NaCl correctly (23 + 35.5 = 58.5).
A1 · 1 mark · Correctly calculates moles = $\frac{5.1}{58.5} = 0.087$ (accept 2–3 sig. figs). (follow-through)
Worked solution
Molar mass of NaCl = $23 + 35.5 = 58.5$ g/mol.
Moles of NaCl = $\frac{5.1}{58.5} = 0.087$ mol.