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JAMB Chemistry 1984 Question 13

Question 13

Acids, Bases and Salts

Which of the following mixtures would result in a solution of pH greater than 7?

  1. A.25.00 cm3 of 0.05 M H2SO4 and 25.00 cm3 of 0.50 M Na2CO3
  2. B.25.00 cm3 of 0.05 M H2SO4 and 25.00 cm3 of 0.10 M NaHCO3
  3. C.25.00 cm3 of 0.11 M H2SO4 and 25.00 cm3 of 0.10 M NaOH
  4. D.25.00 cm3 of 0.11 M H2SO4 and 50.00 cm3 of 0.05 M NaOH
  5. E.25.00 cm3 of 0.25 M H2SO4 and 50.00 cm3 of 0.20 M NaOH.
Show the answer and explanation

Answer: A (25.00 cm3 of 0.05 M H2SO4 and 25.00 cm3 of 0.50 M Na2CO3)

Explanation

In A there are only 1.25 mmol of H2SO4 but 12.5 mmol of Na2CO3, so excess carbonate makes the solution alkaline. In C, D and E the acid is in excess, and in B the acid and hydrogencarbonate just neutralise each other.