Equipment
- Measuring cylinder
- Conical flask
- Stop clock
- Thermometer
- Cross on piece of paper
- Small beaker
- Medium beaker
- Large beaker
- Safety glasses
Method
I am going to measure out 50cm³ of Sodium Thiosulphate solution using a measuring cylinder, pour it into a conical flask and record the temperature using a thermometer. Then I will measure out using a different measuring cylinder 10cm³ of Hydrochloric acid. I will then place the conical flask containing the Sodium Thiosulphate on top of the cross and add the Hydrochloric acid to the conical flask. When the Hydrochloric acid first hits the Sodium Thiosulphate I will start the stop clock. I will look down on the conical flask and when the whole cross has disappeared the stop clock will be stopped and the time recorded. I am going to repeat the experiment three times for each of the set of measurements, which are
I will make my experiment a fair test by wearing safety glasses and by following the lab safety rules.
Earlier work
Earlier work that I have done which helped me to plan my practical work is “How does the concentration of Hydrochloric acid affect the rate of its reaction with Magnesium.” The results were as follows
The experiment shows that as the concentration increases, so does the rate of reaction.
Results
Observing patterns in results
Looking at my results table, the average time graph and rate graph, I can see a clear pattern in the results. The average time graph shows a smooth, steady decreasing curve. This indicates the concentration of Sodium Thiosulphate increases the time taken for the reaction decreases. The rate graph shows that as the concentration of Sodium Thiosulphate increases the rate of the reaction also increases. I had expected a directly proportional relationship between the concentration of sodium Thiosulphate solution and the rate of reaction i.e. as one doubles, so does the other but after drawing construction lines they showed that my expectation was incorrect.
Conclusion
I have found out from my investigation that as the concentration of Sodium Thiosulphate increases, the rate of reaction increases. My results table also shows me as the concentration increases, the time taken for the reaction to happen decreases.
My conclusion is correct because the collision theory states that the higher the concentration means a larger number of particles in a given volume. If there are more particles, there will be more collisions. More collisions mean a larger number of successful collisions. Therefore the rate of reaction increases.
My prediction is correct because it is the same as my conclusion they both say that as the concentration of Sodium Thiosulphate increases, so to does the rate of reaction. My results show this because my rate of reaction graph shows that the line of best fit is getting steeper as the concentration is increasing, this means that the rate is also increasing.
Evaluation
I think my method was a good way of carrying out the investigation because it was quite accurate and was easy to complete.
If I did the investigation again I would use a water bath to keep the temperature of the water, Sodium Thiosulphate and Hydrochloric acid the same. Also instead of using a cross on a piece of paper and observing it until it disappears which is not very accurate. I would put a light sensor underneath the conical flask and connect it to a computer. This would tell me accurately when no more light was coming through the conical flask.
I think my results were reasonably accurate because after doing two repeats I found the numbers around the same area. There were no results that were totally in the wrong place, instead there were a couple that were a few millimetres off the line of best fit on my rate graph. This could have happened because my experiment could have been more accurate if I had used light sensors and water baths.
Other experiments that I could do to extend the work I have done is the effect of the concentration of acid on the rate of reaction with marble chips to see if I get similar findings or I could see how temperature effects the rate of reaction on the experiment I have just done by keeping the volume of Sodium Thiosulphate and Hydrochloric acid the same throughout the experiment and changing the temperature of one of them.