Question

question 5
1 pts
which of the following is insoluble in water at 25 °c?
mg₃(po₄)₂
ba(c₂h₃o₂)₂
na(oh)₂
(nh₄)₂co₃
cs₂s

Explanation:

Step1: Recall solubility rules

Phosphates (\(PO_{4}^{3 - }\)) are generally insoluble except when with Group - 1 metals (e.g., \(Na^{+}\), \(K^{+}\)) and \(NH_{4}^{+}\). \(Mg_{3}(PO_{4})_{2}\) has \(Mg^{2 + }\) (not Group - 1 or \(NH_{4}^{+}\)).

Step2: Check other options

• Acetates (\(C_{2}H_{3}O_{2}^{-}\)): Most acetates are soluble. \(Ba(C_{2}H_{3}O_{2})_{2}\) is soluble.
• Hydroxides (\(OH^{-}\)): \(Na^{+}\) (Group - 1) hydroxide (\(NaOH\), note correct formula is \(NaOH\) not \(Na(OH)_{2}\), but if we assume it's a typo for \(NaOH\)) is soluble.
• Carbonates (\(CO_{3}^{2 - }\)): \(NH_{4}^{+}\) carbonate \((NH_{4})_{2}CO_{3}\) is soluble (rule: carbonates are insoluble except with Group - 1 and \(NH_{4}^{+}\)).
• Sulfides (\(S^{2 - }\)): \(Cs^{+}\) (Group - 1) sulfide \(Cs_{2}S\) is soluble (rule: sulfides are insoluble except with Group - 1 and \(NH_{4}^{+}\)).

Answer:

\(Mg_{3}(PO_{4})_{2}\)