Factors that Affect the Rate of a Chemical Reaction

Factors that Affect the Rate of a Chemical Reaction
I am going to plan and carry out an investigation into one factor that affects the rate of a chemical reaction. That chemical reaction is going to be between sodium thiosulphate solution and dilute hydrochloric acid. To make this a fair test we will have to keep all variables the same except the one we area investigating. My variable that I am going to investigate is going to be the concentration of the sodium thiosulphate. Sodium thiosulphate solution and dilute hydrochloric acid produce a solid (seen as cloudiness). I am going to time how long it takes for the solid to block out a cross underneath a conical flask. From the time taken I can calculate the rate of reaction by working out 1/time (units s-1). Variables The variables that may have an affect on this experiment are: ? The amount of sodium thiosulphate ? the more sodium thiosulphate the more it is in contact with the acid so it will react at a different speed. I am going to be changing the concentration of this. ? The concentration of the Hydrochloric acid ? this is the proportion of hydrochloric acid in the solution. ? The volume of acid ? this is the amount of acid used to react with the sodium thiosulphate. ?
Temperature ? adds energy to the reaction and can therefore speed up the reaction ? The cross ? has to be the same amount to be a fair test, if the cross was not the same size each time then the results could be different ? Residue after each experiment ? if the residue builds up it could block visibility on the next experiment. Prediction I predict that the higher the concentration the faster the reaction will take place this is because in a higher concentration there will more hydrochloric acid molecules per set volume. This means that there will be a higher chance of the sodium thiosulphate molecules colliding with the hydrochloric acid and reacting. This should in theory increase the rate of reaction as the concentration is increased. This on a rate of reaction graph will have a positive correlation. The increase in the concentration should be directly proportional to the increase of the reaction rate at a given time. This is because by doubling the number of hydrochloric acid molecules present the chance of a collision should be doubled, as there is now twice the possibility of a collision-taking place. This can be thought of as like people in a refined space, if there is twice the number of people there will be twice the chance of people colliding. Safety Simple procedures that can ensure a safer environment in the lab. ? Wear safety goggles as we are dealing with corrosive substances ? Tuck the stools in so nobody trips and falls ? Tuck in bags so nobody trips and falls ? Stand up in case there is a spillage so we can get out of the way quickly ? As the reaction produces carbon dioxide, which is poisonous, it will be put in a sealed container Controls ==== Sodium thiosulphate solution ? 25cm3 per reading Volume of acid ? 5cm3 per reading Concentration of Sodium thiosulphate solution ? The investigated variable Concentration of acid ? 1.0 mol/dm3 Temperature ? Room temperature Cross ? Written on paper to be the same each time Apparatus ===== 25cm3 Sodium thiosulphate solution 5cm3 dilute hydrochloric acid 1.0 mol/dm3 100cm3 Conical flask Paper with cross on Stop Clock Measuring cylinder Safety goggles Method == 1. Safety goggles and lab coats were put on 2. 25cm3 Sodium thiosulphate solution with concentration of 0.25 mol/dm3 was added to a conical flask that was above a piece of paper with a cross on it. 3. 5cm3 of hydrochloric acid was added to the conical flask and the timer was started. 4. As the reaction happens the solution turns cloudy. The timer is stopped as the cross is unable to been seen. 5. The result is filled in the results table. 6. The experiment is repeated but with the 25cm3 Sodium thiosulphate solution with concentration 0.2 mol/dm3. 7. The experiment is repeated but with the 25cm3 Sodium thiosulphate solution with concentration 0.17 mol/dm3. 8. The experiment is repeated but with the 25cm3 Sodium thiosulphate solution with concentration 0.15 mol/dm3. 9. The experiment is repeated but with the 25cm3 Sodium thiosulphate solution with concentration 0.13 mol/dm3. Results === The experiment will be repeated with each concentration 3 times then the average will be used in the evaluation. This will make it a fair test. If there is an anomaly result then it will be done a forth time so it will not alter the average. Concentration of sodium thiosulphate mol/dm3 1st time 2nd time 3rd time Average Rate of reaction (1/time) 0.25 35.80 35.99 37.20 36.33 0.028 0.2 40.09 42.34 40.28 40.90 0.024 0.17 44.50 47.60 45.93 46.01 0.022 0.15 64.87 58.18 60.59 61.21 0.016 0.13 66.69 67.07 72.75 68.83 0.015 Diagram Analysis In my first graph it shows all the results on a line graph. The crosses that are circled are anomalies as they are more than a centimetre from the other two results out of the three. The anomalies are not in the equation for working out the average. The rate of reaction is then worked out and put on my second graph. Conclusion I Have come to the conclusion that the higher the concentration the faster the reaction. This is because my results give pretty conclusive evidence that as the amount of Sodium Thiosulphate decreases, and the amount of water in the solution increases there are less atoms to collide and therefore less successful collisions causing chemical change so the reaction rate is slower. In a more concentrated solution, there are more atoms to collide so the reaction time is quicker. My results support my prediction as I said, " The higher the concentration the faster the reaction will place". The rate of reaction graph shows a positive correlation, which also proves my prediction, is correct. Evaluating Evidence Many parts of my experiment could be improved. ? I could have more accurate measurings by using a burette as is more precise and can have readings of up to a tenth of an ml. ? When washing the conical flask with water I didn?t dry it every time and so there was water in the flask when the two chemicals were added and therefore the reaction could of bee diluted even more ? My eyesight is not perfect and I could not of stopped the stop clock as soon as the cross had been blacked out. A more efficient way of measuring this would to be a to use a light measuring computer. So the stop clock would stop when a certain amount of light was blocked out resulting in more accurate results My results are good in their accuracy and the points on the graph were plotted as accurately as possible. Although, I did get some anomalous results but that is to be expected. All my ?good? results fitted my prediction and made a strong trend in the graphs. I tested my results 3 times to ensure that I had not made any mistakes, and I also did preliminary work in order to familiarise myself with the project, set-up and equipment and to see if there was a better way of doing the experiment. I repeated each experiment three times to get an average which would help cancel out anomalies. I got a couple of anomalies due to simple human error i.e. accidentally putting in the wrong proportions when diluting the sodium thiosulphate. If I were to do the experiment again I would do things more slowly to stop human errors due to being rushed. I would use the improvements above.

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