For each of the following compounds, decide whether the compound's solubility in aqueous solution changes with pH. a. Ca(OH)2
b. CuBr
c. Ca3(PO4)2

a. pH raises

b. pH neutral

c. pH raises

Explanation:

First of all we need to dissociate these compounds.

Ca(OH)₂ →  Ca²⁺  +  2OH⁻

This is the calcium hydroxide, a strong base.

In this case, we are giving OH⁻ to medium, so the pH will be increased.

OH⁻  +  H⁺  ⇄  H₂O

Hydroxides will neutralize the protons in order to make water, but if we have many OH, we talk about a basic solution where pH is lower than 7.

b. CuBr → Cu⁺  +  Br⁻

This is similar to NaCl, a ionic salt which is neutral.

The ions from this salt, do not make hydrolisis, that's why pH does not change.

c. Ca₃(PO₄)₂ → 3Ca²⁺  +  2PO₄⁻³

Calcium cathion comes from a strong base. It means, that the ion can not make hydrolisis because it is the conjugate weak acid.

Phosphate anion comes from a weak acid, it can gives OH⁻ to medium so pH will increase; the PO₄⁻³ anion is the conjugate strong base of the phosphoric acid, that's why it can react:

PO₄⁻³ + H₂O  ⇄  H₂PO⁻²  +  OH⁻

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