KINETICS OF THE REACTION BETWEEN SODIUM THIOSULPHATE AND HYDROCHLORIC ACID.

 

Aim

The purpose of this experiment is to determine the rate equation for the reaction between sodium thiosulphate and hydrochloric acid by determining the order of reaction with respect to sodium thiosulphate and hydrochloric acid.

 

Introduction

Sodium thiosulphate and hydrochloric acid react according to the stoichiometric equation

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

 

The rate equation for the reaction is in the form

            Rate = k [Na2S2O3]s [HCl]t

Where k is the rate constant 

            s is the order of reaction with respect to sodium thiosulphate and t is the order of reaction with respect to hydrochloric acid.

 

You will be determining the order of reaction for each reactant by varying the concentration of each species in turn, keeping the others constant.

The reaction can be followed using the precipitated sulphur which causes the solution to become opaque.  The rate can be determined by measuring the time taken for a line drawn on a piece of paper and placed under the reaction vessel to become obscured.

 

Apparatus                                                        Chemicals

3 x 50 ml burettes                                             0.2M sodium thiosulphate solution

2 x 100ml beakers                                            1M hydrochloric acid

0-100 oC thermometer                                      distilled water

stop clock

glass stirring rod

 

Procedure

A         Varying the concentration of Na2S2O3

 

1                    Set up three burettes in stands for hydrochloric acid, sodium thiosulphate and distilled water.

 

2                    Add 10 cm3 of the hydrochloric acid solution to a 100 cm3 beaker labelled X.

 

3                    In a separate beaker (Y) place 30 cm3 of the sodium thiosulphate solution and 10 cm3 of water.

 

4                    Draw a line on a piece of paper and place beaker Y over it

 

5                    At a convenient time pour the acid from beaker X into beaker Y and start a stop clock.

 

6                    Stir the solution well with a glass rod and watch the line through the solution in beaker Y.

 

7                    Stop the clock when the line on the paper just disappears.

 

8                    Record the time and the temperature of the mixture in the results table.

 

9                    Repeat the procedure for the rest of the mixtures in the table below.

 

 

Beaker X

Beaker Y

Volume of HCl /cm3

Volume of Na2S2O3 /cm3

Volume of water /cm3

10

30

10

10

25

15

10

20

20

10

15

25

10

10

30

10

5

35

 

10        Complete the results table.