Calculate the mass of a 20% hydrochloric acid solution that will require 18 g of iron hydroxide 2.

1. Let’s compose the equation of the chemical reaction:

Fe (OH) 2 + 2HCl = FeCl2 + 2H2O.

2. Find the chemical amount of iron hydroxide:

n (Fe (OH) 2) = m (Fe (OH) 2) / M (Fe (OH) 2) = 18 g / 90 g / mol = 0.2 mol.

3. According to the reaction equation, we find the chemical amount, and then the mass of hydrochloric acid:

n (c) = n (Fe (OH) 2) * 2 = 0.2 mol * 2 = 0.4 mol.

m (HCl) = n (HCl) * M (HCl) = 0.4 mol * 36.5 g / mol = 14.6 g.

4. Find the mass of the hydrochloric acid solution:

m (solution) = m (HCl) * 100% / ω (HCl) = 14.6 g * 100% / 20% = 73 g.

Answer: m (solution) = 73 g.