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The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid - page 6
Keywords: The determining of a rate equation from the reaction of sodium thiosulphate with hydrochloric acid
By Carlitob10 on 04/11/2006 11:57:07
Level: A Level (Year 13)
Page Number: 6 of 8 pages: 1 2 3 4 5 6 7 81 (please see separate page), where the concentration of 2.0M hydrochloric acid is held constant and the concentration of 0.4M thiosulphate is varied systematically. We can see that, as the concentration of thiosulphate doubles, then the rate also doubles (from 0.03 s-1 at 0.15M to 0.06 s-1 at 0.3M). Therefore we can write:
Rate [S2O32- (aq)]
Let us now look at table 2 (please see separate page), where the concentration of 0.4M thiosulphate is held constant and the concentration of the 2.0M hydrochloric acid is varied systematically. We can see that as the concentration of acid doubles, the rate of reaction also doubles (from 0.02 s-1 at 0.1M to 0.04 s-1 at 0.2M), and so on. Therefore we can write:
Rate [H+ (aq)]
Combining the two reaction rates gives:
Rate [S2O32- (aq)] [H+ (aq)]
Therefore, the rate equation is:
Rate = k [S2O32- (aq)] [H+ (aq)]
The reaction is first order with respect to [S2O32- (aq)], because in the rate equation the power to which this concentration is raised is 1. It is also first order with respect to [H+ (aq)], because the power to which this concentration is raised is also 1.
Conclusion & Evaluation
Precision of measurements & accuracy of experiment:
Experimental error is always with us; it is in the nature of scientific measurement that uncertainty is associated with every quantitative result. This may be due to inherent limitations in the measuring equipment, or of the measuring techniques, or perhaps the experience and skill of the experimenter. It goes without saying that, when conducting this experiment, I endeavoured to be as careful and as accurate as I could in my measurements. However, there are several areas where precision could be improved:
• I had to measure out my reagents and water using three burettes, which were set up on one of the lab benches. I found these a little difficult to read at times, as they were placed significantly higher than eye level. Therefore, it was not always possible for me to measure out these volumes as accurately as I would have liked.
• I should have started the stopwatch at the exact time I put the water and the sodium thiosulphate into the conical flask containing the acid. This is not always possible when conducting the experiment alone, as it is also important to
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