DP Chemistry (last assessment 2024)

Question 21N.2.hl.TZ0.c

[Maximum mark: 2]

21N.2.hl.TZ0.c

Phosphoric acid, H₃PO₄ can form three different salts depending on the extent of neutralisation by sodium hydroxide.

Calculate the concentration of H₃PO₄ if 25.00 cm³ is completely neutralised by the addition of 28.40 cm³ of 0.5000 mol dm⁻³ NaOH.

[2]

Markscheme

« $NaOH \frac{28.40 {cm}^{3}}{1000} \times 0.5000 mol {dm}^{- 3} = 0.01420 mol$ »

« $\frac{0.01420 mol}{3} =$ » 0.004733 «mol» ✔

« $\frac{0.004733 mol}{\frac{25.00 {cm}^{3}}{1000}} =$ » 0.1893 «mol dm⁻³» ✔

Award [2] for correct final answer.

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