Calculate the mass of 60% acetic acid used to neutralize 120 g of 25% sodium hydroxide solution.
Given: w (CH3COOH) = 0.6; mp-pa (NaOH) = 120 g; w (NaOH) = 0.25.
Find: mр-ra (CH3COOH) -?
1. We write down the equation of the proceeding reaction:
CH3COOH + NaOH → CH3COONa + H2O.
2. Find the mass of sodium hydroxide:
m (NaOH) = w (NaOH) * mr-pa (NaOH) = 0.25 * 120 = 30 g.
3. Calculate the chemical amount of sodium hydroxide:
n (NaOH) = m (NaOH): M (NaOH);
M (NaOH) = 23 + 17 = 40 g / mol;
n (NaOH) = 30:40 = 0.75 mol.
4. According to the equation, the acid reacts with alkali in a 1: 1 ratio, set the amount of acetic acid:
n (CH3COOH) = n (NaOH) = 0.75 mol.
5. Determine the mass of acetic acid:
m (CH3COOH) = n (CH3COOH) * M (CH3COOH);
M (CH3COOH) = 12 + 3 + 12 + 32 + 1 = 60 g / mol;
m (CH3COOH) = 0.75 * 60 = 45 g.
6. Let’s calculate the mass of the acid solution:
mр-pa (CH3COOH) = m (CH3COOH): w (CH3COOH) = 45: 0.6 = 75 g.
Answer: 75 g.