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The aim of these experiments is to investigate how concentration affects the rate of reaction between two chemicals.

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Introduction

Sodium Thiosulphate GCSE Coursework The aim of these experiments is to investigate how concentration affects the rate of reaction between two chemicals. Planning For our investigation we will be using Sodium Thiosulphate and Hydrochloric Acid. We chose these chemicals, because visual changes take place when the two are mixed together. Combining them will produce a yellow precipitate, and this will make it easy for us to measure the rate of reaction. To investigate the effect concentration has on reaction rates, we must vary the concentration of one of the two chemicals used. Sodium Thiosulphate and Hydrochloric Acid are both soluble in water, so it would be possible to alter the concentration of either of them. However, we have decided to vary the concentration of the Sodium Thiosulphate because [REASON]. To measure the rate of reaction, we will be using light sensors connected to a computer. The solution of Thiosulphate will be poured into a glass beaker, with the light sensor positioned beneath it, as shown below. ...read more.

Middle

This will mean that in our results, as the concentration of the Thiosulphate drops, it will take longer for the light level to stop dropping and become stable. For a reaction to take place the particles have to successfully collide with each other. As the concentration falls, there will be less Sodium Thiosulphate particles in the solution. This lowers the chance of collisions between the Sodium Thiosulphate and the Hydrochloric Acid particles, and so it also lowers the chance of successful collisions between them. Results For our results we have collected data in two formats. Firstly we collected graphs, constructed by the computer which used information from the light sensor. Secondly we took the graphs and recorded the time it took in each experiment, for the % of light to level out and become stable. This data is recorded in the table below. Concentration (Thiosulphate/Water) Time Taken for Light(%) to Level Off (Minutes) 50/0 40/10 30/20 20/30 10/40 Analysis From the evidence obtained I can see that, as the concentration of the Sodium Thiosulphate decreases, so does the rate of reaction. ...read more.

Conclusion

The fact that we surrounded the sensor, beaker and lamp ensured that no extra light from the room would interfere with our results. The use of the computer and the light sensor eliminated the possibility of human error in timing and recording results, which also made the final results more accurate. However, despite our attempts to control these conditions, there was one anomaly in our results, where one graph crossed over another. This however was most likely due to a change in temperature around the beaker or in the room in general. If I were to repeat this experiment in the future, I would also try to control the temperature of the liquids, by using insulated beakers, or by conducting the experiment in a room with a controlled temperature. Due to a lack of time, we were only able to conduct each experiment in the investigation once, which could make some of the evidence collected unreliable. To improve the reliability of the evidence we collected, the experiments could have been repeated and an average taken from all of the results. ...read more.

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