IB Chemistry SL R3.1 Proton transfer reactions questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

Four monoprotic acids are prepared as aqueous solutions at the same temperature and with the same initial concentration. Which sample contains the weakest acid?

Show answer and explanation

Answer: B. At equal initial concentration and temperature, the weakest acid ionizes to the smallest extent. Sample S has the smallest ionized fraction, 5%, so it is the weakest.

A: Q is partially ionized, but choosing it ignores the still smaller ionized fraction for S.
C: P has the greatest ionization, 100%; this reverses the relationship and identifies the strongest acid.
D: R has a smaller ionized fraction than Q, but its 20% exceeds S’s 5%.

Remember: compare the extent of ionization, not the initial concentration.

Question 2

Paper 2Medium5 marks

An aqueous sodium hydrogencarbonate solution is tested with a pH probe. At $25\,^\circ\mathrm{C}$ the pH is 8.30. At this temperature, neutral water has $[\mathrm{H^+}]=1.00\times10^{-7}\ \mathrm{mol\,dm^{-3}}$

A student concludes that $\mathrm{HCO_3^-}$ can act only as a Brønsted–Lowry base because the solution is alkaline.

(a)

Calculate $[\mathrm{H^+}]$ in the solution, in $\mathrm{mol\,dm^{-3}}$ to two significant figures.

[1]

(b)

Using your answer to (a), determine whether the solution is acidic, neutral or alkaline.

[1]

(c)

Write equations with state symbols to show $\mathrm{HCO_3^-}$ acting as a Brønsted–Lowry acid and as a Brønsted–Lowry base in water. Use the equations to assess the student's conclusion.

[3]

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