Things tend to go wrong at higher temperatures because at higher temperatures (60i??C+) the dissolved calcium hydrogen carbonate starts to decompose. This removes the temporary hardness and therefore removes the dissolved Ca2+ and Mg2+ ions, therefore making the test unfair because at lower temperatures there was hardness in the water. From the results obtained it has been seen that the rate of reaction increases as the temperature increases, supporting my hypothesis in which I stated that ”As the temperature increases, so will the rate of reaction, but at higher temperatures the pattern (link) will break down (giving us unreliable results and the trend in the graph will show this).
Therefore the Alka-Seltzer tablets dropped into the hottest water will dissolve the fastest. ” As you can see from the graph, at 80i?? C the link breaks down, giving us a result that does not fit in with the general trend of results. This is not an anomalous result and there is a reason behind this.
Things tend to go wrong at higher temperatures because at higher temperatures (60i?? C+) the dissolved calcium hydrogen carbonate starts to decompose. This removes the temporary hardness and therefore removes the dissolved Ca2+ and Mg2+ ions, therefore making the test unfair because at lower temperatures there was hardness in the water.
The graph showing the time in seconds (rate of reaction), against the temperature shows the rate of reaction increasing with the temperature, and there is a curve that at first goes down steeply, but then becomes straighter.
At 80i?? C the link breaks down, giving us an odd result, which can be explained by the fact that the Ca2+ and Mg2+ ions are removed due to the decomposing of the calcium hydrogen carbonate. As you can see from the graph and my table of results, the result obtained at 30i?? C is an anomalous result (i. e. it doesn’t follow the general trend).
This again supports my hypothesis in which I stated this by saying that the link would break down giving us unreliable results. The link did not break down at 60i?? C as I had stated that it would because that is only the temperature at which the Ca2+ and Mg2+ ions started to decompose and once they had fully decomposed the results showed this. For the 1/time(s) against the temperature (i?? C) graph I got a straight line, which was the line of best fit.
Again it shows how unreliable the results are at higher temperatures, as the results for 70i?? C and 80i?? C do not fit in.showing how the link breaks down due to dissolved substances in the water. This shows that the temperature is inversely proportional to the time. Also I predicted that as the temperature increased by 10i?? C the rate of reaction would approximately double.
The results do not clearly show this happening, but I believe that it shows some signs of this happening. At 20i?? C the average time is 97. 5 seconds. When the temperature was increased to 30i?? C it approximately doubled (x 2. 17 to 3 significant figures) to 45 seconds. However this is an anomalous result and should be higher.
Even so, this still supports my prediction. The next result obtained is for 40i?? C, which is 37 seconds. There is no sign of the rate doubling (x 1. 22 to 3 significant figures), but if we take into account that the previous result should have been higher, then it would appear to approximately double. From here onwards it does not double for every 10i?? C. This is due to my theory (scientific background knowledge) that things go wrong at higher temperatures due to the decomposing of calcium hydrogen carbonate at temperatures of 60i?? C and above. Evaluation:
I have obtained a reliable set of results, with repeats of the evidence obtained. An accurate procedure was used, with this being shown by the results obtained which all agree with each other. By using a burette, it allowed me to work up to a very accurate degree of accuracy, rather than simply using a beaker or a measuring cylinder. However, I did use a measuring cylinder for repeat results and this did not seem to affect my results. I obtained one set of anomalous results. These were obtained for a temperature of 30i?? C and did not fit in with the general trend.
According to the best-fit line on my graph, the rate of reaction should have been longer and it should have taken about 58 seconds for the Alka-Seltzer tablets to dissolve in water with a temperature of 30i?? C. A reason for me obtaining this anomalous result could have been due to the fact that whilst the reaction was taking place the 100ml beaker was still in the water bath. This would have caused the temperature to rise slowly and slowly increase the rate while the tablets were dissolving, therefore causing more collisions and increasing the rate.
This did not happen however at higher temperatures, because the temperature of the water bath was about the same, and so it did not really have much effect, and it just kept the temperature constant (i. e. stopped it rising or falling). Although I tried my best to make the experiment perfect there were some unavoidable inaccuracies with the experiment. Firstly, when testing lower temperatures, the temperature of the water bath, which was much higher than the actual temperature being tested, caused a rapid increase in the temperature, or if it were lower it would cause it to decrease rapidly, especially when taken off the Bunsen.
These gave us results for inaccurate temperatures to which were we testing. To overcome this problem, a thermostatic water bath would need to have been used, since it can be set to a certain temperature, and it will stop when it reaches there. Also it would mean that the solution inside it would reach the exact temperature or close to it. , and not increase or decrease once the water inside it has reached equilibration.
Secondly, it was impossible to say when exactly the Alka-Seltzer tablets had completely dissolved and consistently decide this for every result obtained. This was a huge flaw in the experiment and affected the results in a big way. To overcome this problem a special piece of apparatus would be needed to decide exactly when they had dissolved each time and give us the same measure of consistency each time. To improve the quality of the results, the same piece of apparatus would have needed to be used throughout the whole experiment, and not changed for repeat results.
To extend my inquiry and provide additional evidence for this experiment, I think that I could have investigated up to higher temperatures and see how the link would break down, and how the results would fit in with the trend of results. Also, it would have helped me to see how the decomposing of the dissolved substances affected the results. To improve the experiment and make it fair, distilled water should have been used instead of tap water because it is purer than tap water and does not contain impurities.
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