Chemistry Gcse Coursework Rates of Reaction

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Science Coursework-Rates of Reactions


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.


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. 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. The reason I could not see the black cross was mainly because the STS particles were reacting with the hydrochloric acid particles and resulted in probably denser particles. I predicted this through this equation: Sodium-thiosulphate + Hydrochloric acid = Sulphur + Sodium Chloride + Sulphur Dioxide + Water. 2HCl(aq) + Na2S2O3(aq) 2NaCl(aq) + SO2(g) +S(s) + H2O(l)

My prediction was clearly accurate as I obtained reliable results independently in my preliminary test which highlighted that my experiment actually worked.

|Sodium-thiosulphate |Water (H20) |Hydrochloric Acid |Time Taken | |(STS) (ml) |(ml) |(HCL) (ml) |(Seconds) (S) | |(1 Molar) | | | | |4ml |28ml |30ml |584s | |40ml |0ml |30ml |41s | |Sodium-thio-sulphate |Water (H20) |Hydrochloric Acid |Time Taken | |(STS) (ml) |(ml) |(HCL) (ml) |(Seconds) (S) | |(2 Molar’s) | | | | |12ml |36ml |30ml |114s...
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