Safety Issues
There are many safety issues that need to be considered while doing this experiment. These include:
- Wearing safety goggles at all times. If acids or any other chemicals are spilt, they would cause serious damage to the skin and eyes.
- Ties and long hair should be kept away from the experiment.
- If an accident occurs, tell the person Incharge.
- Any loose items must be removed.
- Stand up while doing the experiment.
- Bags or any other obstructions should be removed.
I have done a preliminary experiment to help me decide the range of concentrations to use and how much of a difference in concentration to leave between each one. My preliminary results also show that 5cm3 is a low enough concentration to begin with. My knowledge tells me that 5cm3 will take longer to react because there are less sodium particles that react with the acid. My experiment is time based and I will not have enough time to go lower. I took 10 concentrations in the preliminary test already, and this should show enough of a trend already, so there is no need to do an even lower concentration, as it would not help my experiment in any way.
Apparatus:
- 100ml conical flask
- Stopwatch
- Thermometer
- Different size measuring cylinders(5ml, 10ml, 50ml)
- Piece of paper.
- Blue or black pen
- Hydrochloric acid
- Sodium Thiosulphate solution
- Water
- Beakers
To keep this a fair test I have made sure that the acid used is the same amount every time. Also the size of the cross on the piece of paper is the same. The temperature is also the same because the results could be anomalous if tested in different conditions. Same beakers will not be used
for different chemicals. This can cause reactions in the beakers and will lead to inaccuracies.
Preliminary Results Table:
Experiment 1 Results:
Experiment 2 Results:
Experiment 3 Results:
My results clearly show that as the concentration decreases, the time increases in the experiment. This links in with the collision theory and this can be explained. A higher concentration means that there are more particles for the hydrochloric acid to react with. This results in a shorter time and the cross on the paper disappearing quickly. A lower concentration means that
there are fewer particles for the hydrochloric acid to react with. This results in a longer time and the cross disappears slowly. My prediction was correct to some extent, because I mentioned the experiment progressing quicker with a higher concentration. However, I was not entirely correct as I predicted that the time would be doubled when the concentration was halved. When the concentration was 40cm3 the time was 20.62, but when the concentration was 20cm3 the average time was 48.59. This is not half the time but it was still quite close. This could be because my prediction was incorrect or it maybe is a human error in measuring of the chemicals and timing.
Evaluation
I think that the experiment was very successful. All my results support my prediction, and I did not have any anomalous results. I was very careful measuring the chemicals out, so I believe this is why I did not have any. My graph has good points plotted and the join to make a smooth curve. I think that a smooth curve is an indication towards good results.
However, I would have got even better results if had more accurate methods of measuring. For example I could have used a computer to measure out the chemicals. Also, I could have used a automatic stopwatch. This would help me to obtain better results that are more accurate. My hand was not very steady in the preliminary experiment and I poured too much acid in some of the experiment. I improved this by using a beaker to pour the acid first and then transferred it to the flask. I would also repeat the experiment after obtaining the results to make sure of the results.
I think my evidence of this experiment is reliable because I did it with precision and carried it out carefully. I thought that I might have some anomalies but there were not any. I can prove this by using my prediction earlier in the experiment. I said that “as concentration is increased the amount of time taken for the reaction is halved.” I would have been perfectly right but I made a mistake while measuring. To improve my results, I would use a wider range of concentration and different acid solutions. This would help me to find a pattern and come to a firm conclusion.
Overall I think that this experiment was a success as I have proved that concentration does affect rate, and I have also found that when the concentration is doubled the rate of reaction is halved. To draw a firm conclusion I would need to get more results, less inaccuracies and better measuring methods.
