1. 25 cm3 of a solution of sodium hydroxide was added to a flask and titrated with a 0.2 mol l-1 solution of hydrochloric acid.
HCl + NaOH → NaCl + H2O
The experiment was carried out three times and the volumes of HCl titrated in each experiment are shown in the table.
| Titration | Volume of 0.2 mol l-1 solution of HCl (cm3) |
| 1 | 11.3 |
| 2 | 10.4 |
| 3 | 10.6 |
Calculate the concentration of the NaOH solution in mol l –1.
2. 20 cm3 of a solution of potassium hydroxide was added to a flask and titrated with a 0.1 mol l-1 solution of hydrochloric acid.
HCl + KOH → KCl + H2O
The experiment was carried out three times and the volumes of HCl titrated in each experiment are shown in the table.
| Titration | Volume of 0.2 mol l-1 solution of HCl (cm3) |
| 1 | 20.6 |
| 2 | 19.9 |
| 3 | 20.0 |
Calculate the concentration of the KOH solution in mol l –1.
3. 10 cm3 of a solution of KOH was added to a flask and titrated with a 0.05 mol l-1 solution of H2SO4.
H2SO4 + 2KOH → K2SO4 + 2H2O
The experiment was carried out three times and the volumes of HCl titrated in each experiment are shown in the table.
| Titration | Volume of 0.2 mol l-1 solution of HCl (cm3) |
| 1 | 15.9 |
| 2 | 15.2 |
| 3 | 15.3 |
Calculate the concentration of the KOH solution in mol l –1.
4. Rhubarb leaves contain oxalic acid, (COOH)2. A pupil found that it required 17 cm3 of 0.001 mol l-1 of sodium hydroxide to neutralise 25 cm3 of a solution made from rhubarb leaves. Calculate the concentration of oxalic acid in the solution given that the equation for the reaction is:
(COOH)2 + 2NaOH à Na2(COO)2 + 2H2O
5. Acidified potassium permanganate can be used to determine the concentration of hydrogen peroxide solution; the solutions react in the ratio of
2 mol of potassium permanganate: 5mol of hydrogen peroxide.
In an analysis it is found that 16.8 cm3 of 0.025 mol l-1 potassium permanganate reacts exactly with a 50 cm3 sample of hydrogen peroxide solution. What is the concentration, in mol l-1 of the hydrogen peroxide solution?
6. Iodine reacts with thiosulphate ions as follows:
I2(aq) + 2S2O32-(aq) 2I –(aq) + S4O62-(aq)
In an experiment it was found that 1.2 x 10-5 mol of iodine reacted with 3.0 cm3 of the sodium thiosulphate solution. Use this information to calculate the concentration of the thiosulphate solution in mol l-1.
7. Vitamin C, C6H8O6, is a powerful reducing agent. The concentration of vitamin C in a solutioncan be found by titrating it with a standard solution of iodine, using starch as an indicator. The equation for the reaction is:
C6H8O6(aq) + I2(aq) C6H6O6(aq) + 2H+(aq) + 2I–(aq)
A vitamin C tablet was crushed and dissolved in some water. The solution was then transferred to a standard 250 cm3 flask and made up to the 250 cm3 mark with distilled water.
In one investigation it was found that an average of 29.5 cm3 of 0.02 mol l-1 iodine solution was required to react completely with 25.0 cm3 of vitamin C solution.
Use this result to calculate the mass, in grams, of vitamin C in the tablet.
8. Hydrogen sulfide, H2S, can cause an unpleasant smell in water supplies. The concentration of hydrogen sulfide can be measured by titrating with a chlorine standard solution. The equation for the reaction taking place is
4Cl2(aq) + H2S(aq) + 4H2O(l) → SO42−(aq) + 10H+(aq) + 8Cl−(aq)
50·0 cm3 samples of water were titrated using a 0∙010 mol l−1 chlorine solution.
(a) Name an appropriate piece of apparatus which could be used to measure out the water samples.
(b) What is meant by the term standard solution?
(c) An average of 29·4 cm3 of 0∙010 mol l−1 chlorine solution was required to react completely with a 50·0 cm3 sample of water. Calculate the hydrogen sulfide concentration, in mol l−1, present in the water sample. Show your working clearly.
9. A compound known as ethylenediaminetetraacetic acid (EDTA) is useful for measuring the quantities of certain metal ions in solution. For example, Ca2+ ions and EDTA react in a 1 mol:1 mol ratio.
It is found that 14.6 cm3 of 0.1 mol l-1 EDTA reacts exactly with a 25cm3 sample of a solution containing Ca2+ ions.
Calculate the concentration, in mol l-1, of the calcium ion solution.
10. Trichloromethane , is insoluble in water. When ammonia is added to the beaker containing water and trichloromethane, the ammonia dissolves in bith solvents giving different concentrations.
is called the partition coefficient.
This can be found by titrating the ammnia in each layer against diluute hydrochloric acid.
(a) How could the end points of the titrations be observed?
(b) The concentration of ammonia in water was calculated from three titrations.
The titre volumes were as follows
1st 24.7 cm3
2nd 24.0 cm3
3rd 23.9 cm3
(c) What volume of dilute hydrochloric acid would be used to calculate the concentration of water in ammonia?
(d) The concentration of ammonia in water was found to be 1.7 mol ℓ-1. For the ammonia in terachloromethane, it was found that 18.4 cm3 of dilute hydrochloric acid, concentration 0.050 mol ℓ-1 was required to neutralise 20 cm3 of the ammonia solution.
(e) Calculate the value for the partition coefficient of ammonia between water and trichloromethane.
11. A 50·0cm3 sample of contaminated water containing chromate ions was titrated and found t require 27·4 cm3 of 0·0200 mol ℓ –1 iron(II) sulphate solution to reach the end-point.
The redox equation for the reaction is:
3Fe2+(aq) + CrO42–(aq) + 8H+(aq) → 3Fe3+(aq) + Cr3+(aq) + 4H2O(ℓ )
Calculate the chromate ion concentration, in mol l–1, present in the sample of water.
12. An average of 21·6cm3 of 0·0150 mol ℓ –1 acidified permanganate solution was required to react completely with the nitrite ions in a 25·0 cm3 sample of river water.
The equation for the reaction taking place is:
2MnO4–(aq) + 5NO2–(aq) + 6H+(aq) → 2Mn2+(aq) + 5NO3–(aq) + 3H2O(ℓ)
Calculate the nitrite ion concentration, in mol l–1, in the river water.
