Fair Test:
In this experiment I am only going to vary one factor. This factor is going to be the concentration of the solution. The volume of hydrochloric acid solution and water needs to be controlled, this is so the different concentrations can be made. This factor is varied four times during the experiment to obtain a wide range of results.
The volume of Hydrochloric acid and Water is altered while the volume of Sodium Thiosulphate is fixed at 20cm³ to ensure the experiment is a fair test. Each variable will be kept the same by measuring the specific amount of solution needed in each concentration. I will do this by using a measuring cylinder; each cylinder used will be the same to ensure that it is still a fair test.
Each experiment I do, I will do repeats to guarantee that my results are accurate, if I think I’ve made a mistake in one part of the experiment I will repeat it to see if there is a big difference in my results.
Equipment:
Below is a list of the equipment I will need to use during the experiment.
- Sodium thiosulphate (NaSO)
- Hydrochloric acid (HCl)
- Water
- Stop watch
- Measuring cylinder
- Beaker (x3)
- Small beaker
- Paper marked with a cross
- Flask
- 20cm³ pipettes (x2)
- Labels
Method:
- When you start your experiment you must decide whether you or your partner will record the results and measure the solutions.
- To pour some Hydrochloric acid and Sodium into two separate beakers from their bottles. Then get another beaker and fill it with water.
- Then label the beakers so you know which beaker has which substance in it.
- When you begin the experiment it is easiest to start making solution at 100% concentration, then work down the scale of concentrations.
- First measure 20cm³ of sodium thiosulphate using a 20cm³ pipette then add it to a small beaker.
- Then use the other 20cm³ pipette you have and measure 60cm³ of hydrochloric acid. To get 60cm³ use the 20cm³ pipette three times. When you use the two pipettes make sure you keep one pipette for the thiosulphate and one for the hydrochloric acid. If u mix both pipettes the chemicals will react and disrupt the experiment.
- When you have to make other concentrations including some water, you can add the water in to the same beaker as the hydrochloric acid, but the hydrochloric acid and thiosulphate must be kept apart until the experiments begins to avoid the chemicals reacting.
- You or your partner (depending on who’s measuring the substances and recording the results) must place the paper marked with a cross under the beaker of thiosulphate. A stopwatch must also be present near by.
- Then pour the hydrochloric acid solution into the small beaker, as soon as all the contents of the beaker are in the other beaker start the stopwatch and start timing.
- The partner assigned to this task must stop the stopwatch as soon as they can no longer see the cross. The cloudiness of the solution is from the two chemicals reacting, this is how we measure the rate of reaction, the faster the cloud appears the faster the rate of reaction.
- Record the results into the table.
- Each concentration is repeated two or three times, this depends on how reliable the results of the experiment appear.
When you use the two pipettes make sure you keep one pipette for the thiosulphate and one for the hydrochloric acid. It is important that you do not mix the different substances into each pipette as the two chemicals will react and it will no longer be a fair test. To make it easier label the two pipettes so they are no mixed up.
Results:
Below is a table of results, which I gathered from the experiments I did. The results of the repeated tests can also be found in the table.
The table below is a table of the averages calculated using the results from the experiment.
Controlling Variables:
Analysing:
The Graph below shows that there is a positive correlation in the results. The graph tells me that if the concentration of the solution is higher, the graph tells me that if the concentration of the solution is higher, the faster the rate of reaction will be. And the lower the concentration the slower the rate of reaction will be. This proves that the prediction I made earlier is correct.
Evaluating:
I think the experiment I conducted was a success. There weren’t any serious problems, which meant I was able to complete the experiment. Nonetheless the accuracy of my results could have been improved. Instead of me and my partner having individual roles we combined the jobs. We didn’t have a set thing to do, we both recorded the results and we both studied the reactivity of the two substances. This isn’t very accurate as one of us might have better eyesight than the other, causing different recordings of the results. It would’ve been more precise if one of us had the job of timing and observing while the other measured and recorded the results. However, we didn’t change jobs often enough for the results to be completely disrupted, just once or twice. This would still count as a fair test, I still believe that this experiment was a success as there were hardly any mistakes made.
