Question

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

Answer 1

a. pH raises

b. pH neutral

c. pH raises

Step-by-step 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⁻