Sulfuric acid was added to 100 g of 20% sodium hydroxide solution until complete neutralization. Calculate the mass of the salt.

Given:

m (NaOH) = 100 g

w% (NaOH) = 20%

To find:

m (salt) -?

Decision:

2NaOH + H2SO4 = Na2SO4 + 2H2O, – we solve the problem based on the composed reaction equation:

1) Find the mass of sodium hydroxide in the solution:

m (NaOH) = 100 g * 0.2 = 20 g

2) Find the amount of sodium hydroxide:

n (NaOH) = m: M = 20 g: 40 g / mol = 0.5 mol

3) We compose a logical expression:

if 2 mol NaOH gives 1 mol Na2SO4,

then 0.5 mol NaOH will give x mol Na2SO4,

then x = 0.25 mol.

4) Find the mass of sodium sulfate formed during the reaction:

m (Na2SO4) = n * M = 0.25 mol * 142 g / mol = 35.5 g.

Answer: m (Na2SO4) = 35.5 g.