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How does Concentration Affect the Speed (Rate) of Reaction.

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How does Concentration Affect the Speed (Rate) of Reaction Planning experimental procedures Introduction I am investigating into the speed of reaction between sodium thiosulphate solution and hydrochloric acid and see how the different concentrations of the sodium solution will affect the rate of this reaction. The formula for this reaction is: Hydrochloric acid particles collide with sodium thiosulphate particles. The sodium and chloride atoms join to form sodium chloride, hydrogen from the hydrochloric acid is oxidised to form water and sulphur from the sulphate combines with oxygen to form sulphur dioxide with sulphur left as a precipitate. This sulphur is the yellowish substance that clouds the water, which we will be using as an indicator to stop the clock. I think chemical reactions are caused due to the collisions of particles of the reactants. When the particles have enough kinetic energy they collide forming products. The energy required to be able to burst through the barrier for a reaction to take place, is known as the activation energy. The rate/speed at which these particles collide depend on various factors. These are: - Surface area of the reactants - Concentration of the reactants - Temperature at which the reaction is being - Use of a catalyst carried ...read more.


2. On a white piece of paper draw a clear cross in black pen. 3. Place the conical flask on top of the cross. 4. In the flask place 20ml of sodium thiosulphate solution and 20ml of hydrochloric acid of 0.5 moles. 5. Start the stop-clock and time how long it takes till the cross completely disappears. 6. Wash out the conical flask and repeat this with all other concentrations of acid. 7. Results should show that the higher the concentration becomes, the quicker the cross will disappear. Fair Test: It is essential that this experiment is carries out fairly to give the most accurate results. 1. The same cross should be used all the time. - This makes sure that each time the same amount of area needs to disappear every time. 2. The same person should do the experiment. - This makes sure the speed is judged equally. 3. The person should see from right above. - This gives the best view and makes sure the whole cross is covered. 4. The same amount of sodium solution and hydrochloric acid should be used. 5. The flask should not be stirred to increase rate of reaction. ...read more.


It was difficult to tell when exactly to stop the clock because even after a long time a faint outline of a cross could be made out. Situations such as these do not make the method so accurate. If I were to repeat the experiment I would repeat all readings again with improved accuracy. I still felt we were not sure about when exactly to stop the cross and I felt we stopped it too early. Each of our results was lower than the expected. For example, for hydrochloric acid with concentration 0.5 moles took 3.01mins, which should ideally be 4mins. ANOMALIES The main anomalies were during the first test, where we stopped the stop-clock too early. We ended up with 2 minutes for the hydrochloric acid with 0.5 moles. As can be seen this affected the averages. OTHER EXPERIMENTS To see what else affects the rate of reaction, I could do experiments investigating the other factors like, temperature and surface area. I could do an experiment between hydrochloric acid and limestone to test the surface area factor. This is a more accurate experiment because to measure how quickly a reaction occurred you could measure: 1) The volume of the carbon dioxide gas which is a product 2) The loss in mass of the reaction in a set time with weighing scales. ...read more.

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