Chemistry Gcse Coursework Rates of Reaction

1 January 2017

Investigating how the concentration of sodium-thiosulphate (STS) and hydrochloric acid (HCL) affects the rate of reaction in the experiment. In addition I am also checking how different variables affect my experiment and also how I can make my test more precise, reliable and accurate. Strategy According to my results, as the concentration of STS solution increased the rate of reaction of my experiment was increased. Also as the concentration of STS solution decreased, the time of reaction increased.

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In my preliminary test I checked my equipment and I came to a conclusion that my equipment was working well. The preliminary test checked if the experiment actually worked and the things I used were reliable for me to use. The method I used to carry out my experiment was very reliable. I first picked the type of experiment I was going to do. Which consisted of many types or variables such as: changing the temperature, catalyst, surface area and concentration etc. As I had limited time I picked concentration. I also had to choose which type concentration I needed either 1 molar or 2 molars (concentration types).

I realised that picking the 1 molar STS solution the rate of reaction was very slow. However in the 2 molar STS solution the rate of reaction was quick. As I was short on time I chose the 2 molar STS solution nevertheless picking this type of concentration could lead me to see more reaction between STS and HCL particles. Therefore allowing me to create an accurate test and allowing me to obtain precise results. Once I decided the concentration I then carried out my experiment. In my preliminary test I carried out my experiment using three beakers which contained of STS, H20 and HCL.

In my experiment I applied H20 so that I could see the rate of reaction through a more dilute solution. I applied all of these solutions in to a conical flask. I recorded my results using a timer just to see if the experiment worked. What I predicted in my preliminary test was, as the sodium-thiosulphate concentration increased, the time taken for the solution to turn cloudy took longer. In this experiment I knew when the solution was completely cloudy was until the black cross underneath the flask had disappeared to my sight.

Sodium-thiosulphate – used as solution as part of my experiment Hydrochloric Acid – used as solution as part of my experiment Beaker – used for carrying the solution Measuring cylinder – used for measuring the volume of solution Timer – used to measure the time taken for the solution to get cloudy Calculator – used to calculate the average time Conical Flask – used to carry out the experiment Black-cross card- used to see weather or not the solution had turned fully cloudy. Collecting Data In my experiment most of the variables I had were: volume of HCL, volume of STS, concentration of HCL or STS, temperature of room, type of apparatus and many more. The variable I changed was the volume of STS and the volume of water.

The variable that I kept the same was the hydrochloric acid which remained at 30ml throughout the whole experiment. By doing so it made my experiment a fair test as I was controlling other variables such as HCL. I kept the other variables the same in order to allow my experiment to be a fair test. Taking temperature into consideration if I did not control this my results would be inaccurate. My experiment was carried out very safely. I made sure that I was wearing my safety goggles whilst I carried out my test. My experiment was placed not in the way of people so that my experiment is not any risk to me or them. In addition the safety rules made my experiment a fair test.

Nevertheless regarding my data of results I had were very reliable and precise as I don’t have any outliers and my graph shows that the increase of STS is directly proportional to the time taken for the solution to become cloudy. To make sure that my test went accurately and precisely I made sure that my timing was accurately done not pressing the timer too early or late. This again shows that my test was a fair test. As the range of volumes of STS I had consisted between 12ml to 40ml although if I applied higher concentrations the test would have been more reliable. However I used these concentration types so that I can get a clear picture that STS reacts with HCL in a certain period of time. I repeated these volumes three times and as a result no outliers had become visible to me on my data. This suggested that my experiment was carried out very accurately.

As well as in my preliminary test I also repeated the test three times so that I could see the results were accurate and precise. Similarly my real experiment was done very precisely such as calculating or measuring the results or measuring the amount of solution in each beaker etc. I predicted that I would find a wrong result whilst doing my experiment, however my prediction was wrong and the results were very accurate. If by chance I found an outlier I would not count it with the rest of my results and I would repeat that test again. One of my problems I encountered during my experiment was the time taken to press the timer which in my opinion affected my results. Interpreting Data

What I notice in my results was that as the concentration of STS kept on increasing the time take for the solution to get cloudy was decreasing. For example when there was 12ml of STS the average time was 140 seconds. Where as when the STS was at 40ml the average time was 32 seconds which shows a very big relationship between the amount of STS and the time taken. This was due to the concentration of the STS solution. In comparison to my preliminary results I can see some similarities between the concentration types of the STS solution. Also I can see on my graph the scatter of results look very accurate and the natural trend of my results shows a negative correlation.

What my graph shows is that the percentage of sodium-thiosulphate increased then the time taken for the experiment decreased. So as the sodium-thiosulphate particles increased which meant that there where more particles colliding with the hydrochloric acid particles. This altogether led to a decrease in the time taken for the reaction to happen. Not only is the results reliable but they are easy to understand as for the key which describes the part on the graph such as line of best fit, error bars etc. Therefore the data I obtained looks very reliable. The picture bellow suggests that if the concentration increases the collision rate increases.

Also many other variables affect the collision rate to increase such as Catalysts and temperature etc. Evaluation In conclusion I think my experiment was very successful. My data is very reliable and accurate as I have no outliers. I probably did not encounter any outliers because the precision and the accuracy I applied to my investigation during timing or measuring etc. this shows the reliability of my investigation. The results could have been improved by repeating the investigation more times so that I can further improve the reliability of my data. On the other hand I am very confident with my results. On my graph the results show very small error bars which suggests that my results again were very accurate.

I was also confidant with the safety of this experiment which mostly when I was pouring out STS and HCL. Therefore this applies to the accuracy of the test. On my table of results I repeated my investigation 3 times to ensure the reliability of my data. Nevertheless I measured the time taken to the nearest second which builds precision in my experiment. I am very confident with the method I used whilst using simple equipment and obtaining fantastic results and my experiment was a success. Overall I am really confident in this investigation, however I can make improvements. Maybe using a better timer to record my results would have granted me more accurate results. I could have also changed the concentration of the HCL solution.

This would make my investigation more of a fair test because during my experiment I used a stronger concentration of the STS solution and so it would have been better if I used the stronger HCL solution. Also safety was equally important to the investigation. I can also improve my experiment by using a turbidity sensor which judges how cloudy things are. By using this turbidity sensor would give me more precise and reliable results. In my opinion this experiment was a very good choice as temperature, surface area and catalysts were also different variable choices, however what I noticed at the start of the experiment was that this investigation was easy to layout and the equipment was available.

My results were outstanding seen as though I had no outliers or the error bars on my graph are very small. The line of best fit shows a natural trend between the solution and the average time taken. But taken into consideration the time taken to record the results was not 100% accurate. This problem would have been avoided if I used more accurate equipment. Taken as a whole I can see that my experiment went very well. I am very confident with my results and I can feel that my investigation was very precise, accurate and my results were extremely reliable. I also feel very confidant that my investigation went well.

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