Question 1

Paper 2Medium5 marks

An aqueous sodium hydrogencarbonate solution is tested with a pH probe. At 25 ∘C25\,^\circ\mathrm{C} the pH is 8.30. At this temperature, neutral water has [H+]=1.00×10−7 mol dm−3[\mathrm{H^+}]=1.00\times10^{-7}\ \mathrm{mol\,dm^{-3}}

A student concludes that HCO3−\mathrm{HCO_3^-} can act only as a Brønsted–Lowry base because the solution is alkaline.

(a)

Calculate [H+][\mathrm{H^+}] in the solution, in mol dm−3\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 HCO3−\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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