The solubility of insoluble substances changes depending on the nature of the solution. Below are two solutions in which copper (II) hydroxide is dissolved; in each case, the solubility is not the same as it is in pure water.

a. For each solution state whether the solubility is greater than or less than that of pure water and briefly account for the change in solubility.
i. 1-molar HCL (aq)
ii. 1-molar copper (II) nitrate (aq)

Cu(OH)2 ==> Cu^2+ + 2OH^-

i. Adding HCl. The H^+ reacts with the OH^- to produce H2O (H^+ + OH^- => H2O), the OH^- is reduced and that shifts the equilibrium to the right (to increase the OH) which means the solubility is increased.

ii. Cu(NO3)2 ==> Cu^2+ + 2NO3^2-

Adding Cu^2+ to the Cu(OH)2 increases the Cu^2+ so the solution must try to reduce the Cu^2+ and it can do that by shifting to the left which decreases the solubility of the Cu(OH)2.

i. In a 1-molar HCl (aq) solution, the solubility of copper (II) hydroxide is greater than that in pure water. This is because HCl is a strong acid that ionizes completely in water, producing a large concentration of H+ ions. The dissolved H+ ions react with copper (II) hydroxide to form soluble copper (II) chloride, which increases the overall solubility of the compound.

ii. In a 1-molar copper (II) nitrate (aq) solution, the solubility of copper (II) hydroxide is also greater than that in pure water. This is because copper (II) nitrate is a soluble salt that dissociates in water, forming Cu2+ ions and NO3- ions. The Cu2+ ions react with hydroxide ions present in the solution to form copper (II) hydroxide, which increases its solubility.

To determine the solubility of copper (II) hydroxide in 1-molar HCl (aq) and 1-molar copper (II) nitrate (aq), we need to understand how the nature of the solution affects the solubility of insoluble substances.

In general, insoluble substances can become soluble in certain solutions due to the formation of complex ions or chemical reactions that break down the insoluble compound. Let's analyze each solution:

i. 1-molar HCl (aq):
- Solubility: Greater than that of pure water.
- Explanation: When copper (II) hydroxide is dissolved in 1-molar HCl, the copper (II) hydroxide reacts with the hydrochloric acid to form a soluble complex ion: Cu(OH)2 + 4HCl -> CuCl4-2 + 4H2O. This complex ion is soluble in the solution, resulting in an increased solubility compared to pure water.

ii. 1-molar copper (II) nitrate (aq):
- Solubility: Greater than that of pure water.
- Explanation: Copper (II) nitrate is already a water-soluble compound. When more of it is added to the solution, it increases the concentration of the copper (II) ions, which can react with the hydroxide ions from the copper (II) hydroxide. This reaction forms a soluble complex ion, allowing more of the copper (II) hydroxide to dissolve. Therefore, the solubility of copper (II) hydroxide is greater in 1-molar copper (II) nitrate compared to pure water.

In both cases, the solubility of copper (II) hydroxide is greater than that in pure water due to the formation of soluble complex ions or the presence of other water-soluble compounds that react with the copper (II) hydroxide.