In my preliminary tests, I tested the reaction of the most concentrated HCl, and the least concentrated. Here are my results:
Initially, I was going to change the concentration of the HCl, however these results are too close together and a small mistake when measuring the reactants would lead to a large error in the results. If I made a 1ml mistake in the 10ml HCl solution, this would lead to a 10% error. If I made a 1ml mistake in the 10ml solution, this would only be a 2% error. So from my preliminary work, I have decided to change the concentration of the Na2S2O3 instead.
Variables
The things that I could change in the investigation are:
Thmperature,
Concentration (of Na2S2O3 and HCl),
Volume of the reaction.
Fair Test
In order to make this a fair test, I will keep the following the same:
Temperature,
Volume
Concentration of HCl
Apparatus
Sodium thiosulphate,
Hydrochloric acid,
Water,
Beaker,
Measuring cylinder (to measure out the correct amounts of HCl, water or Na2S2O3),
Timer (in minutesm seconds and hundredths of seconds),
Burette.
Diagram
Method
From my preliminary work, I have found that if the measurements of Na2S2O3 and HCl are similar, the reaction take a comparatively long time so in order to speed up the reaction, I will use the following measurements:
10ml of HCl and…
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50ml of Na2S2O3.
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40ml of Na2S2O3 and 10ml of water.
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30ml of Na2S2O3 and 20ml of water.
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20ml of Na2S2O3 and 30ml of water.
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10ml of Na2S2O3 and 40ml of water.
Firstly, I am going to measure out 50ml of Na2S2O3 with a measuring cylinder into a beaker. Then I will ad 10ml of HCl and start the timer. When the X cannot be seen, i.e. when they have reacted, I will stop the timer and make a note of the result. I will then repeat this experiment with the other four sets of measurements.
Results
Then I repeated the experiment twice more to make sure my results were accurate.
The highlighted results are anomalies and have been left out my averages to make them accurate.
These are my average results:
Analysis
From the investigation I have found that as the concentration increases, the time of the reaction decreases i.e. the rate increases.
I have also found some trends in my results, when the concentration is doubled, the rate doubles. The concentration and the rate are in direct proportion. This is because when the number of particles in the reaction doubles, the number of successful collisions doubles, some the rate does.
In my prediction, I stated that as the concentration increased, the rate of the reaction would increase with it, this has been proven in my results. This happens because an increase in concentration produces more collisions. The chance of an effective collision goes up with the increase in concentration. E.g. in my experiment, when the concentration was at 30ml of Na2S2O3 the reaction rate was 15.6s-1, and when the concentration was increased to 40ml of Na2S2O3 the rate also increased to 23s-1. I did not however, predict the relationship between the rate and concentration; this they are in direct proportion. This was shown in my results by my rate of reaction graph. When the concentration is 10ml of Na2S2O3 the rate is 4.2s-1. When the concentration is doubled to 20ml of Na2S2O3 the rate also doubles to 10s-1. When the concentration is doubled again, to 40mlof Na2S2O3 the rate again doubles as well, to 22.5s-1.
My results agree with my prediction in that the rate increases as the concentration does, however I did not predict that they would be in direct proportion.
Evaluation
My results were what I expected to get in my prediction, i.e. the rate increased when the concentration did. But I did not expect them to be in direct proportion.
I had some anomalies in my results; in my first experiment 20ml of Na2S2O3 gave me 75.52 secs, and in my second experiment 10ml of Na2S2O3 gave me 202.64 secs. These anomalies are identified on my result graph. These anomalies could have occurred for numerous reasons; I could have made a mistake when measuring out the reactants, or taken my eye off the x and not realised the reaction was complete. This suggests that the quality of my results was not good enough to support my conclusion, however I carried out the experiment three times so that any anomalies in one of the three could be left out of my final average results and they would be more accurate.
The procedure carried out gave me results that were in line with my prediction, so it would seem to be a reliable process. It could be improved, however, by using a bulb and light sensor to automatically produce a graph of results, this would mean that the only possibility of error would be when measuring the reactants. This could have it’s disadvantages as the bulb would be close to the reaction, so could effect the temperature of the reactants, therefore increasing the rate of the reaction, so it would be a fair test.
I could further investigate the rate of reactions by doing an experiment to see how temperature or volume of reactants affects the rate of reaction.