Science Rates of Reaction

April 12, 2018 General Studies

?Reaction Rate Coursework Aim To see how the concentration of a reactant affects the rate of reaction, in this case sodium thiosulphate and acid. Scientific Background For a reaction to occur, the particles of the reactants must be colliding with each other with enough energy, the amount of energy needed for the reaction is called activation energy. Activation energy is altered by temperature, concentration, surface area of and the pressure on the reactants.

Stirring the reactants also increases the rate of reaction because the particles are travelling at a higher speed therefore less time will be taken for a sodium thiosulphate molecule to collide with an acid molecule. Prediction As the concentration of sodium thiosulphate increases, the time it takes for the reaction to complete will decrease, less with each higher concentration. Fair Test

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Because this experiment is only conducted to see how the concentration of a reactant affects the rate of reaction, other variables must be kept the same for it to be a fair test: the same person is going to watch the reaction; a thermometer can record the room temperature to make sure that it’s consistent throughout the experiment; the other variables will stay consistent without interferences; none of the reacting solutions will be stirred. Equipment List 2. Large beaker 3. 2 small beakers 4. Large measuring cylinder (25ml) 5. Small measuring cylinder 6. Dropper 7. Flask 8. Stop-clock

Method 9. Write ‘water’, ‘sodium thiosulphate’ and ‘acid’ across a piece of paper then draw a shape. 10. Fill up the large beaker with sodium thiosulphate and place it over the word on the paper. 11. Fill up one of the small beakers with acid and the other with water then place each over its word on the paper. 12. Fill up the large measuring cylinder with 25ml of sodium thiosulphate, use the dropper for corrections. 13. Use the dropper to fill up the small measuring cylinder with 2ml of acid. 14. Pour sodium thiosulphate into the flask; place it over the shape on the paper. 15.

Pour the acid into the flask, start the stop-clock at the same time. 16. Watch the mixture until the shape underneath it cannot be seen, stop the stop-clock at the same time. 17. Record the time in seconds in a table. 18. Wash out the flask and place it back over the shape. 19. Work out the next concentration of sodium thiosulphate and fill up the measuring cylinder with that amount. 20. Add water to the sodium thiosulphate until it fills up to 25ml. 21. Use the dropper to fill up the small measuring cylinder with 2ml of acid. 22. Repeat steps 7-10. 23. Repeat the same process for all the other concentrations.

Results Tables Trial Run Results: Reaction time(sec) 1st Try 2nd Try Average 75% 46. 46 52. 37 49. 665 50% 73. 50 72. 96 73. 23 25% 189. 82 199. 22 194. 52 Results Table (1st attempt): Reaction time(sec) 1st Try 2nd Try Average 100% 40. 43 42. 50 41. 465 90% 59. 56 43. 32 51. 44 80% 71. 59 60. 43 66. 01 70% 73. 32 63. 84 68. 58 60% 78. 15 62. 22 70. 185 50% 86. 37 86. 37 40% 137. 27 137. 27 30% 189. 12 189. 12 Results Table (2nd attempt): Reaction time(sec) Repeats 1st 2nd 3rd 4th 100% 38. 68 32. 02 34. 17 47. 24 35. 59 35. 115 90% 47. 87 47. 09 47. 01 47. 323 80% 44. 37 46. 41 47. 06 43. 75 38. 6 44. 01 41. 68 43. 691 70% 62. 75 48. 12 47. 64 48. 96 48. 24 60% 51. 63 55. 78 55. 64 52. 63 58. 84 54. 904 50% 60. 72 60. 06 72. 56 70. 36 65. 82 65. 904 40% 83. 38 95. 34 87. 01 80. 41 89. 37 80. 56 98. 06 87. 733 30% 135. 32 142. 37 138. 56 158. 15 138. 75 20% 235. 22 238. 06 176. 56 236. 18 236. 487 (Bold numbers in italics are outliers) Conclusion (Results evaluation for prediction) The results from the trail run proves the prediction to be right; the results from the second attempt also fit in quite well with the prediction, except for the 90% concentration which was probably a mistake.

However, the results from the first attempt suggests that as the concentration decreased, the time taken for the reaction increased steadily in response until it suddenly began to increase very slowly then start to increase steadily again. Also, the ranges between the results for each concentration in every attempt were wide, and on the graph it was clear that each attempt had ended up with different mean values for the same concentrations, some even had a real difference between them.

Despite the wide ranges and odd results, the trend seen on the graph was similar for all three attempts and agrees with the prediction. Evaluation Overall the experiment had been conducted with success; however, there wasn’t enough time during the first attempt to repeat the 50% to 30% concentration, therefore during the second attempt the whole class did the experiment together (i. e. dividing up the concentrations between groups). There was a huge flaw to this though; different people have different eyes thus their opinion of when the shape under the flask disappears varies too.

Also, the amount of light around the room varies which also affects when the shape under the flask becomes imperceptible. This experiment could be improved by using a light metre to define when the reaction is completed; the flask could be placed on a light source, then instead of using eyes to determine when the solution has become opaque, the light metre measures the intensity of the light emitted from the light source through the flask of mixture, and when the intensity drops to a certain percentage, stop the stop-clock; this ensures that the opaqueness of the solution is the same each time.

Need to know: 24. What to write about the graph (if I have to); do I have to draw them separately. 25. What is the gradient of 3 points; how to work it out; why is it needed; where to include it; what to write about it (if I have to).


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