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Introduction

Determining the of the Effect of the Concentration of Na2S2O3 on the Rate of Reaction In this experiment we reacted different concentrations of Na2S2O3 (aq) with a constant volume of HCl, and measured the time it took for the X drawn under the beaker in black marker to disappear. The equation for this reaction is: Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O The concentration of the Na2S2O3 used in the making of these solutions is 0.2M. For Trial 1 and Trial 2 these are the measurements of the volumes of each solution: Solution Volume of Na2S2O3 (aq) (cm³)(±0.1) Volume of H2O (l) (cm³) (±0.1) Total Volume of Na2S2O3 (aq) and H2O (cm³)(±0.2) Volume of HCl (cm³) (±0.2) 1 10.0 40.0 50.0 5.0 2 20.0 30.0 50.0 5.0 3 30.0 20.0 50.0 5.0 4 40.0 10.0 50.0 5.0 5 50.0 0.0 50.0 5.0 These are the results for the time taken with each concentration for both Trials: Solution Time for Trial 1 (±0.4)(s) Time for Trial 2 (±0.4)(s) 1 125.2 133.2 2 61.4 65.1 3 40.0 36.7 4 29.1 29.8 5 24.1 23.4 Uncertainty Details: 1. The uncertainty in the volume of Na2S2O3 (aq) and H2O (l) is given by manufacturer of the burettes. As we find the change in the volume in the burette, the uncertainties are added, and the uncertainty in the volume is ±0.1cm³ 2. ...read more.

Middle

all experiments, so even though we do not know the change in concentration of each reaction, we know that it is about the same. Therefore if we plot 1/time against concentration, we should be able to see the relation between the concentration and the rate, even though we do not have the correct rate. Concentration of Na2S2O3 (aq) (M) Uncertainty in Concentration (M) 1/time (Rate) (mol dm-3 s-1) Uncertainty in Rate (mol dm-3 s-1) 0.0400 ±0.0006 0.00774 ±0.00002 0.0800 ±0.0007 0.0158 ±0.0001 0.1200 ±0.0009 0.0260 ±0.0003 0.160 ±0.001 0.0339 ±0.0005 0.2 Unavailable (0) 0.0420 ±0.0007 Now we can plot this: - As we can see in this graph, it is linear, and Rate is proportional to 1/time. This means that the order of the reaction with relation to Na2S2O3 is 1. Also as the gradient of the line is 0.2166, this tells us that in the rate equation K = 0.2166mol-1dm3s-1. So the rate equation is: Rate = 0.2166[Na2S2O3][HCl]y. However we do not know the order of HCl as we did not vary the volume of HCl. Conclusion To conclude, we have calculated the order of the reaction with respect to Na2S2O3 to be 1. This was efficiently experimentally calculated as shown by the graph above. The graph is very fitting, and there are no anomalous points on it. ...read more.

Conclusion

The temperature could have been monitored during each trial so we can see when the rate could have been affected by a rise/fall in temperature. Also if the room was air-conditioned at a constant temperature, this would have meant the room temperature would stay the same (assuming no windows/doors are opened in the time). The uncertainty in the stop watch was much smaller than the actual uncertainty, so I attempted to find my reaction time, which was 0.4. However, when conducting the experiment it is impossible to tell if every time my reaction time was that, as it may have been more or less. This may have increased or decreased the uncertainty here. I could have taken a larger range of samples for my reaction time to get a more accurate value. As I poured the HCl and started the stop watch at the same time, this meant there was a small delay between when I poured the HCl in and when the stop watch was started. This means that the time was a little bit less than it had to be, once again adding to the slight systematic error. I could have gotten a fellow class mate to press the stop watch as soon as I poured the HCl in, so that there was a much small delay, and more precise results, as well as a smaller systematic error. ________________ [1] Information from http://en.wikipedia.org/wiki/Light_meter Last accessed 02/26/2013 ...read more.

This student written piece of work is one of many that can be found in our International Baccalaureate Chemistry section.