Workshop Christer Gruvberg

Kinetic studies on thiosulfate decomposed by acid


Kinetik der Thiosulfat-Zerlegung durch Säure

 

Dr. Christer Gruvberg

Swedish Microscale Chemistry Center

gruvberg@kreativkemi.se  

                                        

Introduction

When a thiosulfate solution is acidified colloidal sulfur is produced.

S2O32-   SO32- + S(s)

Acid can be used to catalyze this reaction. You will investigate how changing the concentration of thiosulfate changes the speed of this reaction.

Materials

Cassette box containing two 8 well strips, four micro-tip pipettes with 0,15 M Na2S2O3 1M HCl, de-ionized water (Fig.5), Topz.

 

Practising the “shake down” technique

a) Add 3 drops of de-ionized water to each well on one strip (Fig. 6).

b) Put the strip upside down on the other strip.

c) Hold them up and use a fast movement downwards with a sudden stop to transfer all the drops to the lower strip. Repeat the technique until all the water has moved over in one shake. Remove the water.

Procedure

d) Add to the strips, the number of drops of solutions in the table below. Turn the colour codes on the strips to the left. Be cautious to hold the pipette vertical and above each well. The drops must fall from the tip of the pipette.

 

     Table 1 Composition of the liquids in the 8 wells of the two strips

 

 

Well

GREEN

 

0,15M Na2S2O3 (aq)

STRIP

 

H2O

RED STRIP

 

1M HCl(aq)

1

10

0

2

2

9

1

2

3

8

2

2

4

7

3

2

5

6

4

2

6

5

5

2

7

4

6

2

8

3

7

2

 

 

 

 

 

e) Place one strip on the two base lines (===) of the box on the bottom of the table above. Number the wells directly on the paper.

f) Use the “shake down” technique to mix the solutions in the two strips. Start timekeeping simultaneously. Place the lower strip on the paper so that the lines can be seen through the strip.

g) Record the time for each well when the visibility of the lines has disappeared.