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# Chemistry rates of reaction with concentration

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Introduction

How does changing the concentration affect the rate of reaction of sodium thiosulphate and acid? Plan I am going to investigate whether the concentration has an effect on the rate of reaction of sodium thiosulphate and hydrochloric acid. There are two important parts of the theory of rate of reaction. Firstly, the reacting particles must collide with each other. There must be sufficient energy in the collision to overcome the activation energy. The rate of a reaction is determined by the factors shown below: 1. Concentration of a solution 2. Temperature 3. Surface area of a solid 4. Pressure of a gas 5. Catalyst A typical graph for the rate of reaction would look like this: For this experiment, the input variable (the factors I am going to change) is going to be the concentration of the solution. The output variables are the temperature, surface area of the solid, pressure of the gas and the catalyst. For a fair test, the output variables have to all be kept constant. Each of these variables affects the rate of reaction in different ways: Concentration Increasing the concentration of a reactant will increase the rate of reaction. This is because if I were to increase the concentration of hydrochloric acid, it would lead to a greater number of acid particles in the same vicinity. This in turn, suggests that the Sodium thiosulphate is being collided with more regularly and so the Sodium thiosulphate will disappear more rapidly, causing the rate of reaction to rise. ...read more.

Middle

These were the results of my preliminary: Volume of solution (cm3) Volume of acid (cm3) Volume of water (cm3) Cm. of hydrochloric acid (m) Temperature of acid solution (oc) Time taken to disappear (s) Rate of reaction (1/s) 50 5 0 2 23 39 50 1 4 0.4 23 10 minutes plus I found out that it took too long for the 'x' to disappear at a concentration of 0.4 and if I continued with this concentration, then I would be here forever. Therefore. I decided to change the concentration to 3.5 m. My new results from the trial experiment were as follows: Volume of solution (cm3) Volume of acid (cm3) Volume of water (cm3) Cm. of hydrochloric acid (m) Temperature of acid solution (oc) Time taken to disappear (s) Rate of reaction (1/s) 50 5 0 2 23 41 50 1 4 0.4 23 102 These results seemed fairly accurate, so I began the experiment. The results helped me finalise my plan because was able to see the differentiation between the concentration and the rate of reaction. The preliminary results corroborated with my prediction. Analysis And Conclusion I collected the data from the experiment and produced a table of results. From these results, I found the average and plotted a line graph of the averages in order to see a trend between the rate of reaction and the amount of concentration of the acid. ...read more.

Conclusion

This would help me obtain more evidence, which would support my conclusion. Further experiments I would do in order to provide additional evidence about the effect of changing the concentration would be to use nitric acid instead of hydrochloric acid to see if the results are the same. By changing nitric acid, it doesn't change much as there is the same amount of particles. It would only help with more evidence to fit my prediction. The equation for this experiment would be: Sodium thiosulphate+ nitric acid = sodium nitrate + water + sulphur dioxide. I would use this method in order to see what the effect of concentration was: 1. Place 50 cm3 of sodium thiosulpahte solution (10g / dm3) in a conical flask 2. Add 5cm3 and 2ml/dm3 of nitric acid to the flask and swirl 3. Start timing how long it takes for the cross on your piece of paper to disappear. Stop timing as soon as this happens 4. Measure the temperature of the reactants with a thermometer before you add the acid and record your results 5. Repeat the experiment at different concentrations by diluting the acid with water each time. This is how I will change the concentration. I will use concentration from 5-1 cm3. If I still wanted to change the experiment a bit more, I would use different concentrations, with a wider range and I would use more in order to be able to plot more results onto the graph. The concentration range may range from 6-0.2. However, I would need more time for this experiment because I am doing more concentrations. ...read more.

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