A salt solution can be acidic,basic,or neutral.When dissolved in water,which of the following salts will make the solution basic: KBr,MgCO₃,NaF,Na₂SO₄,and CrCl₃?

Question

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To determine whether a salt will make a solution basic, we need to check the ions produced when the salt dissolves in water. If the salt produces the conjugate base of a weak acid (i.e. a stronger base), then the solution will be basic. MgCO₃ produces Mg2+ and CO3^2- ions. CO3^2- is the conjugate base of the weak acid HCO3^- (bicarbonate), so it will react with water to produce OH^- ions, making the solution basic. NaF produces Na+ and F^- ions. F^- is the conjugate base of the weak acid HF (hydrofluoric acid), but it is a very weak base and does not significantly react with water to produce OH^- ions. Therefore, NaF will not make the solution basic. Na₂SO₄ produces Na+ and HS^- ions. HS^- is the conjugate base of the weak acid H2S (hydrosulfuric acid), but it is a weak base and does not significantly react with water to produce OH^- ions. Therefore, Na₂SO₄ will not make the solution basic. MgCO₃, NaF, and Na₂SO₄ are eliminated, leaving choices (A), (C), and (D). CrCl₃ produces Cr3+ and Cl^- ions. Neither Cr3+ nor Cl^- are the conjugate base of a weak acid, so they will not react with water to produce OH^- ions. Therefore, CrCl₃ will not make the solution basic. Thus, the best choice is D, because MgCO₃ and Na₂SO₄ will make the solution basic.

A Salt Solution Can Be Acidic,basic,or Neutral