Question

A known mass of NaOH is dissolved in water to make 1 litre of the solution. 10 mL of the solution requires 20 ml of 1 M HCl. Molar mass of NaOH is 40 g/mol. The number of grams of NaOH in the original solution is

Answer 1

Moles of HCl = Volume of HCl in L$\times$Molarity
= $0.02\times 1=0.02$ mol
From the stoichiometric balanced equation,
$HCl+NaOH\to NaCl+H_{2}O$
Number of moles of HCl = Number of moles of NaOH
Hence, number of moles of NaOH present in 10 mL solution = 0.02 mol
Number of moles present in one litre = $\frac{0.02\times 1000}{10}$ = 2 mol
Number of grams = moles $\times$ molecular weight = $2\times 40$ = 80 g