WAEC SSCE - Chemistry - 1990 (Objective)

Question 1 Report

Which of the following salts in aqueous solution will have a pH greater than 7?

NaCl

ACI₃

FeCI₃

Na ₂SO₄

K ₂CO₃

Answer Details

The salt that will have a pH greater than 7 in aqueous solution is K₂CO₃. When a salt is dissolved in water, it may undergo hydrolysis, which is a chemical reaction between the ions of the salt and the water molecules. Depending on the nature of the ions, the hydrolysis of a salt can result in an acidic, basic or neutral solution. K₂CO₃ is a salt of a strong base (KOH) and a weak acid (H₂CO₃). When it is dissolved in water, the carbonate ions react with water molecules to produce hydroxide ions (OH^-) and bicarbonate ions (HCO₃^-). HCO₃^- + H₂O ⇌ H₃O⁺ + OH^- The presence of hydroxide ions in solution makes it basic. Therefore, the pH of a solution of K₂CO₃ in water will be greater than 7. In contrast, NaCl, ACI₃, FeCI₃, and Na₂SO₄ do not contain hydroxide ions or any other ions that can significantly affect the pH of the solution. They will therefore result in neutral solutions with a pH of 7. Therefore, the answer is K₂CO₃, because it is the only salt of the options given that will produce a basic solution with a pH greater than 7.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)






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