Question

which of the following phosphate salts are insoluble in water? a (nh₄)₃po₄ b li₃po₄ c na₃po₄ d k₃po₄ e ca₃(po₄)₂

Explanation:

Step1: Recall solubility rules

Phosphates are generally insoluble, except for those of ammonium ($NH_4^+$) and alkali - metal cations (Group 1 elements: $Li^+$, $Na^+$, $K^+$ etc.).

Step2: Analyze each option

• Option A: $(NH_4)_3PO_4$ contains ammonium ion, so it is soluble.
• Option B: $Li_3PO_4$ contains lithium (an alkali - metal), so it is soluble.
• Option C: $Na_3PO_4$ contains sodium (an alkali - metal), so it is soluble.
• Option D: $K_3PO_4$ contains potassium (an alkali - metal), so it is soluble.
• Option E: $Ca_3(PO_4)_2$ contains calcium (not an ammonium or alkali - metal), so it is insoluble.

Answer:

E. $Ca_3(PO_4)_2$