Calcium hydroxide was dissolved in water weighing 250 g. When an excess of potassium carbonate acted

| April 25, 2021 | education

Calcium hydroxide was dissolved in water weighing 250 g. When an excess of potassium carbonate acted on this solution, a 3 g precipitate was formed. Calculate the mass fraction of calcium hydroxide in the original solution.

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

Ca (OH) 2 + K2CO3 = CaCO3 ↓ + 2KOH;

2.Calculate the chemical amount of calcium carbonate:

n (CaCO3) = m (CaCO3): M (CaCO3);

M (CaCO3) = 40 + 12 + 3 * 16 = 100 g / mol;

n (CaCO3) = 3: 100 = 0.03 mol;

3.Set the amount of calcium hydroxide:

n (Ca (OH) 2) = n (CaCO3) = 0.03 mol;

4. find the mass of calcium hydroxide:

m (Ca (OH) 2) = n (Ca (OH) 2) * M (Ca (OH) 2);

M (Ca (OH) 2) = 40 + 16 * 2 + 2 = 74 g / mol;

m (Ca (OH) 2) = 0.03 * 74 = 2.22 g;

5.Calculate the mass of the initial solution:

m (solution) = m (H2O) + m (Ca (OH) 2) = 250 + 2.22 = 252.22 g;

6.Calculate the mass fraction of calcium hydroxide:

w (Ca (OH) 2) = m (Ca (OH) 2): m (solution) = 2.22: 252.22 = 0.0088 or 0.88%.

Answer: 0.88%.



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