Question

5) The solubility of Ca (OH)2 is 1.75 g/L. If 3.5 liters of water are 65% saturated with Ca(OH)2, what is the pH of this water?

Answer 1

Ca(OH)2 is a strong base, meaning it completely dissociates into its constituent ion in water as follows:

Ca(OH)2 is a strong base, meaning it completely dissociates into its constituent ion in water as follows: Ca(OH)_2 (aq) rightarrow Ca^2 +_(aq) + 2OH^-(aq) Given that the solubility of Ca(OH)2 in water is 1.75 g/L. Hence, a completely saturated solution of Ca(OH)2 contains 1.75 g of Ca(OH)2 per litre of water. It is mentioned that our solution of 3.5 L is only 65% saturated. Hence, amount of Ca(OH)2 in our solution is 1.75 g/1 L times 3.5 L times 65/100 almostequalto 3.98 g Molar mass of Ca(OH)2 is 74.093 g/mol Hence, number of moles of Ca(OH)2 in the solution is mass/molar mass = 3.98 g/74.093 g/mol = 5.37 times 10^-2 mol Each mole of Ca(OH)2 dissociates into 2 moles of OH-ions. Hence, number of moles of OH-ions in the solution is 2 7 5.37 times 10^-2 mol almostequalto 1.07 times 10^-1 mol Total volume of the solution is 3.5 L Hence, concentration of OH-in the solution is

Given that the solubility of Ca(OH)2 in water is 1.75 g/L.

Hence, a completely saturated solution of Ca(OH)2 contains 1.75 g of Ca(OH)2 per litre of water.

It is mentioned that our solution of 3.5 L is only 65% saturated. Hence, amount of Ca(OH)2 in our solution is

Molar mass of Ca(OH)2 is 74.093 g/mol

Hence, number of moles of Ca(OH)2 in the solution is

Each mole of Ca(OH)2 dissociates into 2 moles of OH- ions.

Hence, number of moles of OH- ions in the solution is

Total volume of the solution is 3.5 L

Hence, concentration of OH- in the solution is

Now we can find the concentration of H+ in the solution by using the following relation:

Hence, pH of the solution can be calculated as

hence, the pH of the solution is approximately 12.49