My aim is to calculate the time it takes for the cross to disappear for each measurement. I will write down the time as soon as I see the cross disappear. I will do each experiment three times and I will take the average for each. I shall do this to make sure the results are as accurate as possible in case one of the experiments we miss calculated and to prevent any bad results.
Measurements:
In this experiment I am going to measure the time it takes for the cross to disappear from my view. I will measure it in seconds and the range will vary in each experiment.
How to carry out the experiment
Step 1- Using a measuring cylinder pour out 50cm³ of sodium thiosulphate solution into a conical flask. Keep this measuring cylinder for this solution only to prevent cross contamination.
Step 2- On a sheet of paper draw a cross and make sure that you use this for the whole experiment, try not to get it wet.
Step 3- Put the conical flask on the piece of paper.
Step 4- Pour hydrochloric acid into another measuring cylinder to the 10cm³ mark, keep this cylinder for the acid only.
Step 5- Pour the acid into the conical flask, as soon as you pour it in start the stopwatch and pour the solution.
Step 6- Look down from above at the cross through the solution.
Step 7- When the cross can no longer be seen then stop the stopwatch and record the time.
Step 8- Wash out the conical flask three times with water.
Step 9- Repeat the experiment but this time mix 40cm³ of sodium thiosulphate and 10cm³ of water. This will make the solution more dilute.
Step 10- Continuing repeating the experiment using the measurements you have chosen.
Step 11- Clear up and dispose of the materials used as instructed by your teacher.
Plan/ method:
I am going to carry out this experiment out by first getting a piece of paper and marking it with a big letter X in the middle. I shall then collect all my equipment and place it at the table so that I am ready to start the experiment. I will then draw up a table of results ready to take down each result as soon as they come. Now ready to start my first experiment I shall measure 50cm³ of sodium thiosulphate. I will then also measure 10cm³ of dilute hydrochloric acid. Once I have both of the measurements I shall first pour the sodium thiosulphate into a conical flask that has been placed above the cross. Once I have done that I will then pour in the dilute hydrochloric acid. As soon as I have poured it in I will then start the stopwatch. After 5 seconds I will stir the solution for 15 seconds exactly, no longer and no less for all the experiments to keep the test fair. Once the cross has fully disappeared I shall stop the time and take the reading down. I will repeat this 3 times so that the experiment is fair and accurate.
For the first experiment I used only sodium thiosulphate and added no water. So for the next experiment I will change the measurement for the sodium thiosulphate so that when water is added the total measurement of the two is 50cm³. For example using 40cm³ of sodium thiosulpahte and 10cm³ of water. The measurement for the hydrochloric acid always stays the same for each case. I shall then do the same experiment as above but this time measuring out 40cm³ of sodium thiosulphate, 10cm³ of water and 10cm³ of dilute hydrochloric acid. I will also repeat this experiment three times to keep it accurate.
Apparatus:
The following is the apparatus that I will be using to conduct my experiment.
- Sodium thiosulphate
- Hydrochloric acid
- 100cm³ conical flask
- 50cm³ measuring cylinder
- 10cm³ measuring cylinder
- Stopwatch
- Paper to mark on cross
- Dark pen to mark the cross on paper
Risk Assessment
It is important that I carry out this experiment in a safe way due to the fact that sodium thiosulphate is being used. To make sure I carry out the investigation in a safe way I shall wear goggles and an apron at all times. I will make sure that the area I am working in is clear and not cluttered with items and keep the floor clear of any obstacles as an extra precaution.
Here is my table of results:
Analysis:
I think that my results were fairly accurate. I made sure that I started the stopwatch as soon as I poured in the dilute hydrochloric acid to the solution and I made sure that I stopped the watch as soon as the cross was no longer visible
I think that overall the experiment worked out as I had planned. I predicted that the more water added the longer it takes for the cross to disappear. I found from my results that my prediction was correct.
My prediction was correct. The higher the concentration the quicker the reaction. This is because when the concentration is high the particles have more energy increasing the amount of successful partial collisions causing the X to disappear quicker.
Conclusion:
Overall I believe my experiment worked well. I made sure the results were as accurate as possible. And all my predictions turned out to be true.
In conclusion I found that the more water that was added the sodium thiosulphate and the dilute hydrochloric acid the longer it took for the cross to disappear.
Evaluation
I feel that in this experiment I had enough evidence to prove my hypothesis. Overall my experiment worked well. There was one anomalous result in the experiment. That was for the 40cm³ of water and 10cm³ of sodium thiosulphate. As you can see on the graph above there was a steady increase in the times then for the last one there was a large gap. This could have been because there was too little sodium thiosulphate and it was very dilute therefore it had less energy and took a long time to react. I feel my evidence was as accurate as it could have been apart from the last time which I feel was an anomalous result.
Anomalous Result
Improvements
I feel that the experiment was fairly accurate but there was still a need for improvement. To make it more accurate instead of using a cross you can use a light meter. You place the light meter in the place of the cross and shine a light from the top of the beaker. When the light meter cannot detect anymore light due to the precipitation (cloudiness) formed it will take an automatic reading. This will make the experiment much more accurate and less prone to human error. I could have also improved my investigation by redoing the experiment which got me the anomalous result so that I could have got a perfect result and as accurate as possible.