Rate is directly proportional to concentration.
Key factors:
No.1: Temperature of the reactants.
As the particles are given heat they gain energy. This causes them to move around at a quicker rate causing a higher percentage of collision within the liquid.
Independent Variable:
Variable equals concentration of Na S O ; this will be changed when we add a higher concentration of the substance after each run. We will do this because it will give us a wider range of results to draw a conclusion.
Factors to keep constant:
Temperature- keep it at room temperature. (Don’t change the area you are doing experiment in).
Light- Keep it in same place
Distance- Stand in same place and use same person to look at the cross.
Cross- Use same cross.
Time- As soon as two substances have been emptied start watch.
Volume- Measure out 25cm3 of HCL each time using same cylinder.
These factors need to be kept the same so the test will be fair.
Dependent Variable:
We will measure the dependent variable by using a watch, when the cross disappears we will stop the watch. We will also make sure that the watch is started at the same time on each concentration. We will do the experiment three times per concentration.
Method:
- Put a cross on the paper and put it under the beaker.
- Put 25cm3 of 0.5m HCL in beaker.
- Then add 25cm3 of 0.03m3 of sodium thiosulphate.
- Stir and start the stopwatch.
- Stop the watch when the cross has fully disappeared.
- Repeat using 0.06m3 of sodium thiosulphate etc.
25 cm3 of HCL (0.5m) and 25 cm3 of sodium thiosulphate (at varying concentrations) are poured out into two measuring cylinders and then poured into a conical flask, which is placed on top of a board marked with letter X. The stopwatch will now be started. When the mixture has turned sufficiently cloudy so that the letter X can no longer be seen the stopwatch will be stopped and the time will be recorded. The experiment is repeated with all the concentrations. The whole procedure is then repeated.
Repeat results and averages will be taken to improve the credibility of the findings, and present solid grounding for the final conclusion. The repeat results will help to solve any anomalies and the average will give a good summary of the results of the experiment. However if one set of results is entirely different to the other, a third experiment will be performed to replace the anomalous set of results.
Results:
Anomalous results: We did not have any anomalous results.
Analysis:
My results supported my prediction to a point, but they were not very accurate so I would have liked to do them again.
Accuracy: The experiment did show that the concentration and temperature did affect the rate of reaction as shown on the graph. Even though the experiment came up with the right results, the method could be improved. There are many ways that the experiment could be improved, one is by being more accurate through the use of a burette, a pipette, a water bath or a light detector, which is controlled by the use of a computer.
Water bath- can be used to make sure that the concentration is the only thing affecting the rate of reaction.
Burette and pipette- ways of making sure that the substances or acids are to the nearest 0.1cm.
Light detector-This is attached to a computer and it’s a way of knowing when the measuring should be stopped. When the substance comes up to the line you are measuring at, the detector will light showing that the right amount of solution has been measured.
Problems-
1) Change in temperature between runs- this would not have been too difficult to keep 2) accurate as a water bath would have been needed. The procedure is not accurate.
3) Errors in measuring out the thiosulphate or acid- this could have been more accurate by the use of a pipette. It is a way of measuring a substance more clearly i.e. 1cm.
4) Stirring- make sure you don’t stir one run and not another, this could cause the solution to cloud quicker.
5) Lighting- Make sure you are in the same position in a room. If the light is any brighter or dimmer it could cause the cross to be seen a lot differently.
The experiment does show a little evidence to confirm my prediction. Ideally I would have liked to repeat the experiment again to gain the best possible accuracy of my results.
At the beginning of the experiment we were supplied with set amounts of concentrations ranging from 0.03M to 0.15M of sodium thiosulphate. We could have gained more accurate results using higher concentrations. E.g. 1.0M etc.
Or the use of better and more accurate equipment. Maybe using a burette or a pipette or even a water bath during the experiment.
Further Investigation-
To carry on further investigation we would have altered a number of things. We could higher the concentration of the sodium thiosulphate. The highest amount we were given was 0.15M; we could go higher and use a concentration of 1.2M etc, to see how the results would compare. We could also change the temperature by using a Bunsen burner and see what a change in temperature does to the experiment. We would do this by changing the temperature. We would add 25 cm of HCL, and 25 cm of sodium thiosulphate (at varying concentrations) into a measuring cylinder, then we would pour them out into two conical flasks. A beaker is half filled with hot water from a tap. The water is placed on top of a Bunsen on a blue flame and the two conical flasks would be placed inside the water bath. The water is heated to the necessary temperature (30ºC to 70ºC) then the two measuring cylinders are taken out and the contents of both are poured into a conical cylinder. The time it takes for the X to disappear is timed and recorded. The experiment is repeated using all the temperatures. The entire procedure is then repeated.
In this experiment I have found that as the temperature and concentration is increased the time taken for the reaction to take place decreases. This means the rate of reaction increasers as it takes less time for a reaction to take place, so more take place per second.
