Find the mass of sodium hydroxide required to completely neutralize 100 g of a 15% hydrochloric acid solution.

Given:

m (HCl) = 100 g

w% (HCl) = 15%

To find:

m (NaOH) -?

Decision:

NaOH + HCl = NaCl + H2O, – we solve the problem based on the composed reaction equation:

1) Find the mass of hydrochloric acid in the solution:

m (HCl) = 100 g * 0.15 = 15 g

2) Find the amount of hydrochloric acid:

n (HCl) = m: M = 15 g: 36.5 g / mol = 0.41 mol

3) We compose a logical expression:

if 1 mol of HCl requires 1 mol of NaOH,

then 0.41 mol HCl will require x mol NaOH,

then x = 0.41 mol.

4) Find the mass of alkali required to neutralize the acid:

m (NaOH) = n * M = 0.41 mol * 40 g / mol = 16.4 g.

Answer: m (NaOH) = 16.4 g.