- Pour both chemicals into a conical flask which has the paper with a cross drawn on it underneath. Take the temperature after the solution is mixed and start the stopwatch. Time how long it takes for the reaction to occur; how long it takes for the mixture to become clouded enough so that you can no longer see the cross underneath the flask.
- Record the results. Repeat the experiment.
Carry out the same experiment using sodium theosulphate and hydrochloric acid at 5°c, room temperature, 30°c, 40°c and 50°c.
The whole experiment should be repeated a second time so that I can gain enough reliable and precise evidence to justify my prediction.
Fair test:
To make this experiment a fair test I will use the same equipment each time I conduct the experiment. I will also not use any contaminated chemicals as this will change the reaction rate. I will use the same method each time I conduct the experiment.
Obtaining Evidence
First set of results:
Second set of results:
I am now going to average these results. I will do this by adding the two results and dividing by two.
e.g. 17 + 16 = 33
33/2 = 16.5
table of average results:
I have plotted the average results on a graph
Graph showing temperature against the rate of reaction
Analysing and considering evidence
The graph shows that as the temperature increases the time taken for the reaction to occur decreases. For example, when the temperature is 28ºc the time taken for the reaction to occur is 23 seconds. As the temperature increases to 33.5ºc the time taken for the reaction to occur has decreased to 19 seconds. This shows that as the temperature increases the rate of the reaction also increases.
Chemical reactions take place when reacting particles collide with each other. The particles which posses energy equal to or greater than the activation energy will be able to move around and collide with other particles to create a reaction. Energy is needed so that existing bonds can be broken so that the particles are free to move around and make new bonds.
Raising the temperature gives the particles more heat energy which then gets converted into kinetic energy. Therefore, the higher the temperature, the higher the level of energy possessed by the particles and therefore the average speed of the particles will be greater. The more energy a particle has the more of a chance it has of reaching the activation energy threshold in collision a collision and causing a reaction.
In conclusion, when the temperature is raised the speed of the particle increases and a larger proportion of collisions transfer sufficient energy for the particles to react. Therefore, the rate of a reaction increases as the temperature increases. This agrees with my prediction.
Evaluation
The quality of the evidence was acceptable for the time and equipment I was given. It was hard to obtain a varied amount of results as the water baths were all set at a certain temperature and it was quite tricky and time consuming obtaining temperatures in between the temperatures set at the water baths.
The evidence is not entirely reliable but is sufficient enough to support the conclusion. There may have been human error involved; the time taken between taking the chemicals out of the water bath and using them in the solution will have changed each time the experiment was conducted. This is because different people involved in the experiment will have worked at a different speed than their lab partners. Also, the experiment was conducted on separate days therefore the room temperature will have changed. There were no anomalies.
To further this experiment, the range and the amount of results could be increased, as well as using different chemicals. To make this experiment more accurate in the future, I could use a computer which would measure the temperature and time so that any possible human error is prevented.
