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Investigating what affects the rate of reaction between sodium thiosulphate and hydrochloric acid

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Investigating what affects the rate of reaction between sodium thiosulphate and hydrochloric acid Aim To investigate what variables influence the rate of reaction between sodium thiosulphate and hydrochloric acid. The specific variable we will be examining will be the amount of acid. Background Information Table of Variables Variables How it will influence my reaction How I will control the variable Temperature When you raise the temperature of a solution, the molecules collide more frequently due to the fact that they have more energy. This means they are more likely to combine and react. When you decrease the temperature, the molecules reduce speed and collide less. The temperature drop lowers the rate of the reaction. I will control the temperature by ensuring the investigation is executed in the same temperature controlled location which will always be maintained at approximately 25�C. Concentration If there is a greater amount of a substance in a solution, there is a greater probability that molecules will collide and speed up the rate of the reaction. The less the substance in the solution, the fewer collisions will occur and the reaction will most probably happen at a slower rate. ...read more.


In this experiment, I tested reacting 100ml of sodium thiosulphate with 100ml of hydrochloric acid 20ml of hydrochloric acid, which were the two extremes of my experiment. I found that the time taken by the reactants to react was reasonable and did not occupy too long or short a time. If the time taken to react was too short, the human reaction time in pressing the stop button of the chronometer will cause a large error margin of approximately �0.5 seconds which will make our results very inaccurate. If the reaction time was too long, it would waste time in which we could be conducting our next experiment without using a large amount of extra equipment. This table shows the results of our preliminary experiments: Amount of HCl (ml) Reaction time with Na2S2O3 (s) 100 78 20 90 Method 1) Put goggles and apron on. 2) Measure 100ml of sodium thiosulphate using a measuring cylinder. I will pour most of the sodium thiosulphate straight from the bottle into the measuring cylinder. ...read more.


That is ample time for me to set up my next experiment where we use 100ml of thiosulphate and 80ml of acid. 8) When the cross is invisible, I will stop the chronometer and record the time in my notebook. 9) I then repeat the experiment using the 100ml of sodium thiosulphate and 80ml of hydrochloric acid. 10) I will do the same experiment using different amounts of hydrochloric acid each time: 100ml, 80ml, 60ml, 40ml and 20ml. 11) I will repeat the experiment for each amount of acid three times so I have three readings for each amount of acid. Analysis I can see from the graph that 4 of the points match my prediction i.e. the amount of hydrochloric acid negatively correlates with the rate of reaction. However there is one point which does not seemingly fit in. When there is 100ml of acid, it takes a longer time for the cross to disappear than with 80ml of acid. The blue line on the graph shows the line of best fit when the seemingly anomalous result is included. However, I do not think the inclusion of an anomaly gives a fair representation of the experiment. The red line shows the line of best fit without the anomaly included. ...read more.

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