%purity

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Step 1: use the equation moles = mass/Mr to calculate how many moles NaOH you would have in 60g of pure sample. Since it is in a 1:1 ratio with H2O (NaOH + HCl -> NaCl + H2O), this is the number of moles of H2O you expect to be produced.

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Step 2: Use the same equation to calculate your expected mass of H2O.

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Step 3: Divide the actual mass by the expected mass of H2O and multiply by 100 for percentage.