Question

For each of the following compounds, decide whether the compound's solubility in aqueous solution changes with pH.

Answer 1

Answer:

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⁻