THEORY:
The effect of temperature on the rate of a reaction can also be studied by following the reaction between sodium thiosulphate and hydrochloric acid under conditions of same concentrations, but different temperatures.
APPARATUS :
Same as in expt. 11.6, and a thermometer.
1) 0.04 M sodium thiosulphate
2) 2M Hydrochloric acid
PROCEDURE:
i) Pour 50 ml of 0.04 M sodium thiosulphate into a clean conical flask from a measuring cylinder. Also have ready 5 ml of 2 M HCL in another small measuring cylinder.
ii) Warm the thiosulphate solution till its temperature is slightly above 20°C.
iii) Place the conical flask over a white filter paper on which a cross mark has been written. Add 5 ml of the acid into the flask, start the stop watch immediately, swirl the flask once, take the temperature and keep the flask still on the filter paper.
iv) Look vertically down through the solution and stop the stop watch when the cross mark just disappears. Note the time in seconds and rinse the flask immediately.
v) Repeat the experiment four times more using 50 ml of 0.04 sodium thiosulphate solution each time at temperatures of approximately 30, 40, 50 and 60°C.
vi) Plot (i) a graph of the time required for the cross to disappear versus temperature. (Take time along the x-axis and temperature on the y-axis)
(ii) a graph of the reciprocal of time versus temperature (take 1/T along the x-axis and temperature on the y-axis)
What conclusion would you draw from the nature of the graphs?
| No. of obs. | Vol of 0.04M thiosulphate (ml) | Temperature °C | Time for the cross to disappear (T) | Recipro-cal of time 1/T |
| 1 | 50 | 20 | ||
| 2 | 50 | 30 | ||
| 3 | 50 | 40 | ||
| 4 | 50 | 50 | ||
| 5 | 50 | 60 |