METHOD: Measure 50cm3 of Sodium Thiosulphate.
Pour this into the conical flask.
Then, measure 10 cm3 of Distilled Water and add to conical flask.
Finally, measure 10 cm3 of Hydrochloric Acid and add to the conical flask.
Start the Stop clock.
Stop the Stop clock when the precipitant has turned cloudy.
DIAGRAM:
Sodium Thiosulphate and 50cm3 Measuring Cylinder
Hydrochloric Acid and 10cm3 Measuring Cylinder 100 cm3 Beaker
Stop-Clock Conical Flask
RESULTS: We did the test several times, so that we could find an average answer to find out
how long it took for the reaction to take place.
1st Test
2nd Test
3rd Test
4th Test40
CONCLUSION: My prediction was correct. I predicted that the more Sodium Thiosulphate there is, the reaction will take place faster because there are more Sodium Thiosulphate molecules and less dilute water molecules for them to collide into. I also predicted that for the reaction to take longer you would use more dilute water molecules, as this will slow the reaction down because there aren’t many Sodium Thiosulphate molecules for the dilute water molecules to smash into together with and to break the Sodium Thiosulphate bonds.
From the 1st graph, I’ve noticed that on the line representing the average tells us that on the first and second point it is nearer to test 2s result. As all three lines start rising, we can know see that the third average point is above both of the lines representing the two tests. On the fourth and fifth point on the average line, it decreases below test 1 and the line representing line 1 increases rapidly.
On the second graph, the points representing test 3, test 4 and the average are quite close together for the 0-50, 10-40, 20-30 concentration. As the points reach the 30-20 concentrations on the graph the points start to spread out and at 40-10 the points are spread out even more. The average point on the 40-10 graph is closer to test 4s point.
EVALUATION: The experiment we did was precise. There weren’t many problems at all. The only problem was that when we measured the Sodium Thiosulphate the first time we did the experiment it went over the 50 marks. When we measured it in the measuring cylinder, to make this a fair test we did not pour the excess back into the bottle, but we spilled it away because the people that would be using it next would have contaminated Sodium Thiosulphate with dilute water. This would make others test unfair. Also, this means that the measurements made on the test was inaccurate.
I think most of our results were accurate. Graph 1 showed a better range of results because they were much more clearly than graph 2 and the results were more spread out. On the 1st test, where the concentration was 10-50, the error in time was inaccurate because we hadn’t noticed whether the concentration had fully turned the milky, cloudy colour, therefore the stop-clock was stopped when the reaction had finished turning the fully cloudy colour.
To change or do the experiment again, I would, change the variables to see whether this would have an effect on the concentration and the rate of reaction. To do this I would, I would keep the Dilute Water. I would change the Hydrochloric Acid so that it was going up in e.g.10, 20,30,40,50 through all the different concentrations and I would keep the Sodium Thiosulphate as 10cm3. This would tell us if we had more Hydrochloric Acid than Dilute Water, would it take quicker or longer for the Dilute Water to break the bonds. If I did this experiment, I think that, the more Hydrochloric Acid there is with less Dilute Water; the reaction will take place faster because the Hydrochloric Acid will be stronger and it will take longer for the Dilute Water to break the Hydrochloric Acid bonds. After this I would do the experiment again to but change the Dilute Water to Warm Dilute Water to see whether the changes have a big difference or a small difference to the outcome of the experiment. This would show whether Hydrochloric Acid has an effect on the rate of concentration.
To improve the experiment I would make sure that the solutions were measured out accurately and I would also make sure that we clean the conical flask thoroughly after each test, so no contents from the last test remains in the next test, this is so that the test can be fair. Furthermore, I would set out the equipment appropriately, so that it is easier to know where all the chemicals and apparatus’s are.
