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Question 19M.2.hl.TZ2.5d(iii)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ2.5d(iii)
Level hl Paper 2 Time zone TZ2
Command term Calculate Question number d(iii) Adapted from N/A
d(iii).
[Maximum mark: 2]
19M.2.hl.TZ2.5d(iii)

Carbonated water is produced when carbon dioxide is dissolved in water under pressure. The following equilibria are established.

Equilibrium (1)  CO2 (g)  CO2 (aq)

Equilibrium (2)  CO2 (aq) + H2O (l) H+ (aq) + HCO3− (aq)

Soda water has sodium hydrogencarbonate, NaHCO3, dissolved in the carbonated water.

(d(iii))

100.0cm3 of soda water contains 3.0 × 10−2g NaHCO3.

Calculate the concentration of NaHCO3 in mol dm−3.

[2]

Markscheme

«molar mass of NaHCO3 =» 84.01 «g mol-1»    [✔]

«concentration =  3.0 × 10 − 2 g 84.01  g mo l − 1 × 1 0.100  d m 3 =» 3.6 × 10–3 «mol dm-3»     [✔]

 

Note: Award [2] for correct final answer.

Examiners report

This is another stoichiometry question that most candidates were able to solve well, with occasional errors when calculating Mr of hydrogen carbonate.

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