Kinetics Study on the Reaction between Sodium Thiosulphate and Hydrochloric Acid

Materials Required

  • Burettes
  • Conical flasks
  • Stop-watch
  • 0.1M sodium thiosulphate (Na2S2O3) solution
  • 1M HCl
  • Distilled water.

Procedure

Real Lab Procedure

  • Take five clean conical flasks and label them as A, B, C, D and E respectively.
  • Add 10, 20, 30, 40 and 50 ml of 0.1M sodium thiosulphate solution to the flasks A, B, C, D and E respectively.
  • Then add 40, 30, 20 and 10ml of distilled water to the flask A, B, C and D respectively so that volume of solution in each flask is 50ml.
  • Add 10ml of 1M HCl to the conical flask A.
  • When half of the HCl solution has been added to the conical flask, start the stop- watch immediately.
  • Shake the contents of the conical flask and place it on a white tile that has a cross mark at the centre.
  • Go on observing from the top of the flask and stop the stop-watch when the cross marks just becomes invisible. Note down the time.
  • Repeat the experiment by adding 10ml of 1M HCl to flasks B, C, D and E respectively and record the time taken in each case for the cross to become just invisible.

Simulator Procedure (as performed through the Online Labs)

  • You can select the volume of sodium thiosulphate (Na2S2O3) solution using the slider.
  • Drag the measuring jar to the conical flask to pour 0.1 M sodium thiosulphate (Na2S2O3) solution in it.
  • Drag the measuring jar to the conical flask to pour distilled water in it.
  • Click on the stopcock of the burette to add 5 ml hydrochloric acid into the conical flask.
  • Click on the conical flask to shake it.
  • Immediately, click on the stopcock of the burette to add another 5ml hydrochloric acid into the conical flask.
  • You can get the time taken for the disappearance of the cross mark from the stopwatch.
  • You can use the embedded worksheet to enter the values.
  • You can plot a graph using the worksheet.
  • To redo the experiment, click the ‘Reset’ button.

Note: Click on the ‘HELP’ button to see the instructions.

Observations

Flask No.    
 
Volume of Na2S2O3 solution (ml) Volume of water (ml) Total volume of solution (ml) Conc. of Na2S2O3 solution (M) Volume of 1M HCl (ml) Time (t) taken for cross to become just invisible (s)
1/t
(s-1)
A 10 40 50 0.02 10    
B 20 30 50 0.04 10    
C 30 20 50 0.06 10    
D 40 10 50 0.08 10    
E 50 0 50 0.1 10    

Plotting the Graph

Plot a graph between 1/t (in s-1) and the conc. of Na2S2O3 by taking 1/t along ordinate axis and conc. of Na2S2O3 along abscissa.

Conclusion

  • The graph obtained is a straight line.
  • 1/t is directly proportional to the concentration of Na2S2O3.
  • Rate of the reaction between Na2S2O3 and HCl is directly proportional to the concentration of Na2S2O3, which is one of the reactant.

Precautions

  • The apparatus must be thoroughly clean.
  • Measure the volumes of sodium thiosulphate solution, HCl and distilled water very accurately.
  • Use the same tile with the cross-mark for all observations.
  • Complete the experiment at one time only so that there is not much temperature variation.
  • When half of the HCl has been added to sodium thiosulphate solution, start the stop-watch immediately.
  • View the cross-mark through the reaction mixture from top to bottom and from same height for all the observations.

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