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# Effect of concentration on rate of reaction

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Introduction

Effect of concentration on rate of reaction Aim The investigation is about the effect of concentration on the rate of chemical reaction. In this experiment I am going to investigate the rate of reaction of sodium litho sulphate with hydrochloric acid. The reaction that I will use is: Sodium litho sulphate + Hydrochloric Acid Na2S2O3 + 2HCl Variables I will change the concentration of hydrochloric acid each time. I will use hydrochloric acid 0.1M, 0.25M, 0.50M, 0.75M and 1M. I will keep the same the amount of hydrochloric acid and sodium litho sulphate concentrations used. I will be measuring the time it takes the sodium litho sulphate to react with hydrochloric acid to form sulphur (a cloudy white colour). Prediction What I think might happen is that the concentrations will mix together and then the concentration will turn to a cloudy colour after it has been mixed. So the smaller the concentration is, the slower the reaction will happen. My reasons for thinking this are that chemical reactions only occur when reacting particles collide with each other. For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. ...read more.

Middle

Repeat the same procedure for the Rest of the reaction but using different hydrochloric acids each time. Use the following hydrochloric acid concentrations after your first reaction: 1. Hydrochloric acid 0.25M 2. Hydrochloric acid 0.50M 3. Hydrochloric acid 0.75M 4. Hydrochloric acid 1M The Sodium litho sulphate stays the same for all the reactions. The measurement that I will make is the time it takes the concentration to react or change to sulphur. In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the Hydrochloric acid and Sodium thiosulphate will not be mixed up. The amount of Hydrochloric acid will be 10ml each time, and the amount of Sodium thiosulphate will be fixed at10ml. All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful. Scientific knowledge Colloids are important in this experiment because the reaction between Sulphur and hydrochloric acid forms a 'colloid', which makes the solution go cloudy. When you use a higher concentration the amount of colloids colliding goes up which means that the rate of reaction is speeded up. ...read more.

Conclusion

In a reaction where one or both reactants are in high concentrations the particles are crowded close together and will collide with each other more often, resulting in an increased number of successful collisions. The surface area affects the rate of reaction because large particles have a small surface area in relation to their volume- less particles are exposed and available for collisions. This means less collisions and slower reaction. Small particles have a large surface area in relation to their volume- more particles are exposed and available for collisions and a faster reaction. The catalysts also affect the rate of reaction. A catalyst is a substance, which increases the rate of chemical reaction, without being used up in the process. Catalysts are specific i.e. different reactions need different catalysts. Because catalysts are not used up, only small amounts are needed. Catalysts work by reducing the activation energy- the minimum energy needed for a reaction to happen. Evaluation My method was a good one because I explained every step and I included some safety precautions for a safe experiment. I can improve the method by including diagrams of each step. My results were reliable and helpful and I can get better results if I done another two readings for each reaction or I can compare them to another person's results. To get the best results I could also work out the averages to find a more accurate reading. ...read more.

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