APPARATUS
In the investigation I will need to use the following apparatus which are as followed:
- A good amount of Sodium Thiosulphate (Na25203)
- A smaller amount of Hydrochloric acid, 2HCL (aq)
- 2 measuring cylinders, one in intervals of 2’s (small) and one in 10’s (large). These will be used for the Na25203 and the 2HCL(aq), the water can be measured in the Na25203 tube because its parochially diluted with water.
- A conical flask should be used for the where the chemicals react.
- Black marker and paper used for the X under the collical beaker.
- Some water used to balance the solution
- And finally a stop clock to measure the time it takes for the reaction to end.
METHOD
Firstly gather all of the apparatus shown above. Once you have gathered them you firstly take your first measurement of Na25203 which could be starting from 10cm3 and then place that into the conical beaker. Once that has been completed you then add your water which would be 40cm3 using the same measuring tube as the Na25203. When that has been carried out you place your beaker onto of the X on the paper, and then add your 5cm3 of Hydrochloric acid, start the stop clock and then shake the beaker to get the reaction going. Remember your solution must be equivalent to 55cm3. (25 + 25 + 5 = 55cm3). When you can not see the X on the paper anymore, you must quickly stop your stop clock and then take down the time it took for the X to disappear. You should carry out the same experiment around 6 times so you can get a good set of results. A tip is to never put any extra amount of a certain chemical such as sodium Thiosulphate and Hydrochloric acid back into the stock bottle it came from because you could easily contaminated the chemical and waste a lot. When you have finished obtaining your results you can then plot them into a table and then work out that rate of the reaction by using the following equation
RATE = 100
time
This is a table that u can use to plot your results.
Obtaining results
I carried my experiment 3 times in order for a fair test, for more accurate readings, and to see if there were any minor or major differences in the time and rate readings.
Here are the 3 series of my results.
1.
2.
3.
Here is a table to show the mean time and the mean rate.
ANALAYSIS
I have plotted several graphs to support my result tables. They consist of, one graph which has the results of the 3 time reading experiments. One graphs which has the results of the 3 Rate equations (100 / time), And finally 2 graphs which distinguish the mean (average) rate and time.
Here are my Graphs.
In my set of results several patterns and trends occurred such as in the first 2 sets of results, the time readings were pretty similar, they were only going out of proportion by only 3-9 figures at the most. On the other hand, my 3rd set of results were different at the start, they were completely different compared to the first 2 sets of results, but gradually evened out to be around the same towards the end of that particular experiment. I will try to explain what may have happened in the Evaluation. My graphs will also show that my experiment when up in steady intervals. My results show that, as predicted, the more concentrated solutions reacted more quickly than the weaker ones. As the concentration got weaker, the reaction was slower. I would expect the same pattern of you swapped Sodium Thiosulphate and Hydrochloric Acid for two other chemicals, which are not affected by water, but will react with each other. The factor/variable that I changed, which was the amount of sodium thiosulphate, effects the reaction by when adding more sodium thiosulphate, the particles in the solution collide more often because there are more particles in the solution.
RED= Hydrochloric acid
BROWN= Sodium thiosulphate
BLUE= H2o
In diagram A there are a lot more thiosulphate particles than in B, so this means that the thiosulphate particles can find the hydrochloric acid particles easier than in diagram B, so the reaction will take place a lot faster. In diagram B there are few thiosulphate particles and a lot of water. The water doesn’t really have a purpose in the experiment it just dilutes the solution and doesn’t take part in the reactance sequence at all. With all of the water in the way the small amount of thiosulphate cant get to the hydrochloric acid particles very easy and thus making the experiment much slower.
Yes my results do support my prediction because I predicted that when more sodium thiosulphate is added and water is taken out ( hydrochloric acid stays at 5cm3 the whole time), then the reaction will be a lot faster. When there is a lot of water and hardly any thiosulphate in the solution, keeping the acid the same, then the reaction will be a lot slower. My results had proven my prediction because when less thiosulphate was added the time it took for the X to disappear took longer thus making the rate not very high.
e.g. (these results were taken from one of my readings)
Thiosulphate. Water. Hcl. Time. Rate.
10cm3. 45cm3. 5cm3. 260s. 0.38.
.
.
..
40cm3. 15cm3. 5cm3. 34s. 2.94.
EVALUATION
In all, my experiment worked quite well. I did come across a few problems with accuracy though. One of the most significant problems was that me and my 2 partners may have not took enough care on checking the time correctly and thus making unneeded errors. It is also quite hard (impossible) to get the exact time that the X has disappeared, an advanced piece of scientific time measuring device would have to be used to get an almost perfect time reading. The first 2 experiments were quite similar to a certain extent, but the 3rd and final experiment I did seems to differ from the others. This could have been due to an insufficient amount of time given in class. Another reason is that keeping track of the correct time could also be a limiting factor to why the readings were odd. My final idea is that my group and me may have not washed the instruments well enough or mixed up certain chemicals. All of these could of made a big difference in to why the readings in the last test were odd.
Several improvements are needed in order for decent fair test and I already mentioned them before. They are basically to watch the X underneath the conical flask until you are sure it has gone, using the same person for checking the X to disappear would help because people’s eyesight can differ and it would help for more accurate results. Washing the apparatus after each test would also help because remains of chemicals used previously could still be lingering somewhere on a test tube, etc. when you are measuring amounts of certain chemicals, you should use a measuring cylinder to get accurate measurements. Instead of using a measuring cylinder, you could weigh the chemicals on electronic scales because you can get much more detailed measurements.
In the future if you wanted or needed to carry out this experiment again, you could perhaps change the amount of hydrochloric acid and keep the sodium thiosulphate the same through out remembering to dilute the solution with water. If you still wanted to prove that when adding more of one chemical, the particles collide more often and cause a faster reaction, you could use different chemicals instead. I couldn’t recommend any but it could prove the theory to a greater extent.
“Factors which effect the rate of a reaction”, by Jason Phelan