*old batch of sodium thiosulphate
Because of lack of time, we had to take the initial trials of the two other groups and use them as our other trials. Our group conducted the second trial.
Trial One
Trial Two
Trial Three
Observations
- As the reaction proceeds, the solution gradually becomes cloudy due to the formation of insoluble sulfur.
- The time it took for the X drawn on the piece of paper and placed under the Erlenmeyer flask to be obscured was shorter with higher concentrations if each reactant.
-
Data Processing
Overview-
The first thing I will do is determine the concentration of sodium thiosulphate and hydrochloric acid at each corresponding volume. Then I will determine the average time taken for an X drawn on a piece of paper and placed under the Erlenmeyer flask to become obscured. Next I will determine the rate of each reactant at each given concentration for either reactant. Finally I will plot separate graphs of 1/time against the concentration of the reactant under consideration.
Sample Calculation-
Concentration of sodium thiosulphate in solution containing 50 cm3 of sodium thiosulphate:
number of moles of Na2S2O3 used = C * V/1000
= 0.1 mol dm-3 * (50/1000 dm3)
= 0.005 mol
concentration of Na2S2O3 (mol dm-3) = n / V
= 0.005 mol / 0.05 dm3
= 0.1 mol dm-3
The molarity of the hydrochloric acid is 1 mol.
Average of different trials for the time taken for an X drawn on a piece of paper and placed under the Erlenmeyer flask to become obscured by a solution with a concentration of 0.1 mol dm-3 of sodium thiosulphate:
(49.7+55.4)/2 = 52.55 s
Average time taken by solution for different sodium thiosulphate concentrations:
Average time taken by solution for different hydrochloric acid concentrations:
Presentation-
If we plot time versus [Na2S2O3], we find the following:
From this graph, we can calculate the rate at various concentrations of Na2S2O3.
If we plot time vs. [HCl], we find the following:
From this graph, we can calculate the rate at various concentrations of HCl.
Conclusion and Evaluation
Conclusion
-
As you can see on the graphs of rate vs. [Na2SsO3] and rate vs. [HCl], the points do not fall exactly on the trend line, indicating an error. They do, however, fall almost exactly where the trend line would expect them to be. Therefore, we can reasonably assume that the expected order of reaction with respect to either reactant is accurate.
- Thus, the rate is first order with respect to sodium thiosulphate, second order with respect to hydrochloric acid and third order overall.
-
Rate expression given by rate = k[Na2S2O3][HCl]2.
