Question

You are supplied with a solution of sodium thiosulphate of unknown concentration. To estimate its

exact concentration, you placed 10 cm3 of 0.1 N Potassium dichromate in a conical flask and titrated

it against the sodium thiosulphate solution by iodometry. You recorded a constant burette reading

of 5.0 cm3

. What is the exact concentration of the thiosulphate?​

Answer 1

Answer:

There are a number of ways to investigate the rate of a reaction in Chemistry. This is an outline of the required steps to undertake one of these methods. It is important in this core practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature and volume.

Aims

To investigate the effect of changing the temperature on the rate of a reaction.

Sodium thiosulfate solution reacts with dilute hydrochloric acid:

Sodium thiosulfate + hydrochloric acid → sodium chloride + water + sulfur dioxide + sulfur

Na2S2O3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + SO2(g) + S(s)

The sulfur forms a cloudy yellow-white precipitate during the reaction. The time taken for this to achieve a given cloudiness provides a way to measure the reaction time.

Method

The result of adding dilute acid to a transparent sodium thiosulfate solution is a more opaque solution.

Using a measuring cylinder, add 50 cm3 of dilute sodium thiosulfate solution to a conical flask.

Place the conical flask on a piece of paper with a black cross drawn on it.

Using a different measuring cylinder, add 10 cm3 of dilute hydrochloric acid to the conical flask. Immediately swirl the flask to mix its contents and start a stop clock.

Measure and record the temperature of the reaction mixture.

Look down through the reaction mixture. When the cross is no longer visible, record the time on the stop clock.

Measure and record the temperature of the reaction mixture, and clean the apparatus as directed by the teacher.

Repeat steps 1 to 6 with different starting temperatures of sodium thiosulfate solution.

Results

Record the results in a table. This table gives some example results.

Temperature (°C) Reaction time (s) Rate

(/s)

18 80 12.5

29 57 17.5

42 32 31.3

49 20 50.0

Analysis

Calculate 1000/time for each temperature. This value is proportional to the rate of reaction.

Plot a graph to show:

reaction rate (/s) on the vertical axis

temperature (°C) on the horizontal axis

a curve of best fit

Explanation: