Fair Test:
In the investigation I will be changing the concentration of the sodium thiosulphate. I change this to see if there is a change in the rate of reaction. I will keep the temperature the same, the size of the conical flask, the temperature, and the volume of the reactants. This will ensure a fair test. Also I will do the whole experiment three times. This will ensure I don’t have any abnormal results.
Prediction:
I predict that the higher the concentration of the sodium thiosulphate the faster the reaction. I think this because there will be more sodium thiosulphate particles to react with the hydrochloric acid. The rate of reaction should increase as the sodium thiosulphate increases, and the amount of water decreases. This means there is a higher possibility of the particle colliding and reacting.
My graph should show a negative, decreasing curve.
Apparatus:
- Safety goggles
- Thermometer
- Stopwatch
- Conical flask
- Burette
- Paper with a black cross
- Distilled water
- Pipette
- Measuring cylinder
- Reactants (sodium thiosulphate, Hydrochloric acid.)
Method:
1. Firstly, using burettes, I will measure out the correct amount of sodium thiosulphate, and distilled water.
2. Using I pipette transfer the measured hydrochloric acid into a measuring cylinder.
3. Put the sodium thiosulphate into a conical flask mix with the water place on top of the paper marked with a cross.
4. Add the acid and start timing simultaneously. Stir the solution for ten seconds.
5. Stop the timer when the cross has fully disappeared.
6. Repeat this three times for each measurement to ensure fair results.
7. Repeat all points only changing the concentration where needed.
Concentrations of sodium thiosulphate:
Safety:
To ensure that the experiment is performed in a safe environment, I will follow these safety rules:
1. Wear goggles at all times
2. Tie back hair, or remove loose clothing (i.e. tie)
3. Store bags and coats in a cupboard out of the way.
4. Move carefully around the lab, No running.
5. Clean up any spillages and immediately inform a teacher.
Results:
Rate of reaction (sˉ¹) = 1
Time taken for x to disappear.
My graphs will now be on the next two pages.
Conclusion:
The experiments made were very successful and we had managed to complete the experiment fully and fairly.
The fastest reaction made was with no water, this reaction is very fast with a time average of 82.3 seconds. The slowest reaction made was with 8 cm³ of water. This reaction was very slow with a time of 703.3 seconds in average. This shows that the higher the concentration of sodium thiosulphate, the quicker the reaction. The time taken for the cross to disappear relies on the concentration of the sodium thiosulphate. This means that the sodium thiosulphate to water ratio is bigger. If there is more sodium thiosulphate to water in the solution then this means that there are more sodium thiosulphate molecules in it. The scientific explanation is the collision theory. The stronger the concentration, the quicker a reaction. This is due to there is more molecules to react with. My conclusion matches my prediction.
Evaluation:
My method of carrying out my experiment was fairly accurate. I made sure that I washed the beakers clean for the other two concentrations and the second experiment, I measured the same amount of solution in each time and I stopped the stopwatch as soon as I thought the cross had disappeared. I think that I should have used five different conical flasks for the five different concentrations because this would be fairer and there wouldn't be any water at the bottom of the beaker. If I was to do the experiment again I could improve the accuracy and reliability of my results by having a wider range of different concentrations. Also I could use the same amount of beakers for the number of different concentrations I use. If I had more time I could do extra experiments to investigate another factor such as the affects of temperature on a rate of reaction. Also I could investigate the affects of pressure on a rate of reaction. Also I would arrange so the experiment could be carried out on the same day. This could make the results more accurate. This could not be carried out since our lessons are only fifty minutes long. Furthermore I could use more sophisticated equipment. This would clear any discrepancies with the judging of the disappearing of the cross. Light sensors could be used.