Method:
- I will gather up the listed equipment.
- I will draw a cross on the paper using a black marker. This will be used in each experiment.
- I will measure the volume of the Sodium thiosulphate to 30ml using a measuring cylinder and pour it into a test tube and then place that into a water bath of using the distilled water.
- I will then place this on tripod and heat it using a Bunsen burner until the temperature is 30°C, this will be measured using a thermometer.
- I will then pour this into a conical flask that will be placed on the cross I drew earlier and it will also contain the 30ml of hydrochloric acid.
- I will start timing the reaction using a stopwatch at the moment I pour the Sodium thiosulphate into the hydrochloric acid.
- I will stop timing when the cross can no longer be seen as the precipitate has formed making the cross obscure. I will record the results in a table.
- The experiment will be repeated for 40°C, 50°C, 60°C, 70°C and 80°C.
Diagram:
The diagram shows what my equipment should look like once set up for one experiment, as it will be repeated for different temperatures.
Safety:
Goggles and an apron should be worn at all times because I will be dealing with corrosive chemicals.
Results:
As well as my own results I used another person’s results to have a bigger range of results therefore a greater accuracy and then I have also made averages for both sets of results.
My results Other person’s results Averages
Analysis:
The results from the graph give a clear indication of how the time compares to the temperature. There is a very strong negative correlation. This means that when the temperature is increased the time decreases for the reaction to take place, all of my results show this do did another persons and consequently the averages shown on the graph show this.
The theory behind this is explained in my prediction, the faster a particle, the more particle kinetic energy it will have so the more likely a particle from the sodium thiosulphate will react with the hydrochloric acid particles. In affect I believe the longer I heat the mixture the faster the rate of reaction will be. This has been proven in my results as I explained before the longer I heated the Sodium thiosulphate the faster the reaction took place, an example of this is shown on the graph where when the temperature was 30°C the time taken was 12.49 second then compared to 40°C the time taken was 9.12 seconds, from theses results you can clearly see that the reaction was speeded up.
The results that I have obtained support my original prediction. This is because in the prediction I said that the longer I heated the Sodium thiosulphate the faster the reaction would take place.
The curve of best fit clearly shows that the results followed the expected pattern very well. The points are very close if not touching the curve.
Evaluation:
I think 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.
Overall, my experiment worked very well. The method that I used in the practical was efficient and my results were reliable.
I think all of my other results were accurate and followed the pattern I predicted previously.
The method I chose to use was very suitable. Following the fair test criteria ensured that my results were accurate, and the experiment was completed appropriately. However, minimal changes could have been made in order to improve the reliability of my evidence.
A factor that perhaps reduced the degree of accuracy was the timing element that was done by using a stopwatch and stopping it when the cross obscured, this requires my judgment for when exactly the cross obscured, so I could have stopped the watch at times when the cross hadn’t fully obscured and at other times after the cross had obscured. To improve the suitability of theses results I could possibly get three people to time the reaction and draw averages from the times, this would improve the accuracy of the results.
I can prove that my experiment was successful because of the graph I drew.
I don't think that by doing any more results in my experiment would improve the accuracy at all. I included my results, my friend’s results and then worked out average for these.
If I had the chance to do the experiment again, I would investigate further by increasing the moles of sodium thiosulphate I used in 0.5 increments i.e. 0.5M, 1M, 1.5M, 2M etc. and then see how the temperature changed against time in this way.
Rates of Reaction Investigation
Aim:
My aim is to investigate how varying the concentration of a chemical affects the rate of reaction.
Plan:
I will vary the concentration of the Hydrochloric acid by adding different volumes of distilled water i.e. diluting it, I will use distilled water because it contains no impurities therefore no other reactions could take place that would affect the outcomes of the experiments. I will also decrease the volume of Sodium thiosulphate so that the total volume of the reactants stays the same, keeping them the same will mean that I will be able to see a pattern. I will pour the diluted Sodium thiosulphate into a conical flask for 1M Hydrochloric acid which I know works from my preliminary experiment, its volume will not be changed again keeping the total volume the same. I will again use the “disappearing cross” method, where I will draw a cross on a piece of paper and place it under the conical flask. As a yellow precipitate forms the cross will become obscure. I will keep the temperature the same for each experiment because I found this out from my preliminary experiment. To find out the rate of reaction I will time it using a stopwatch, this method was quite accurate as I found out from my preliminary experiment.
Preliminary Experiment:
A preliminary experiment (see Appendix) was carried out; this involved investigating how the rate of reaction is affected by temperature. In the experiment Sodium thiosulphate and hydrochloric acid were also used, this was done to become more familiar with the reaction between these two substances. The experiment followed a similar procedure to this investigation but the Sodium thiosulphate was heated to temperatures ranging from 10 - 80°C using 10 °C intervals. From the experiment I found out that the rate of reaction increased as the temperature increased. In this experiment temperature will be kept constant so that I can get reliable results showing how the concentration of a chemical affects the rate of reaction.
Predictions:
I predict that as the concentration of Sodium thiosulphate decreases the time for the reaction to take place will reduce.
I believe this to be true because the less molecules of the Sodium thiosulphate there is less probability of they being a reaction as the reactants have less chance of colliding with each other. When there are more reactant particles there is larger probabilities of collisions taking place hence a reaction taking place, but as I am going to be diluting the sodium thiosulphate I am decreasing the amount of reactant particles, so the less likely a reaction is to take place.
Fair Test:
To ensure that the investigation is carried out in a fair way and that the results will be accurate and reliable a number of things must be followed. I will use the same cross on paper using a black marker for each experiment because this will mean that there will be little error of judgment on the precise moment the cross has obscured.
Equipment:
The equipment I will need to carry out this investigation is as follows:
Beaker – Will be used to contain chemicals such as Sodium thiosulphate and these can be then easily transferred into the conical flask 0.5M Sodium thiosulphate – This is the reactant I am going to be using, I will be varying its volume 1M Hydrochloric acid – This is the other reactant I will be using and I will be using the same volume of this Distilled water – This will be used because it has no impurities therefore no unauthorized reactions can take place Measuring Cylinders – Will be used to measure the reactants Stop watch – This will be used to determine the rate of reaction Conical Flask – The reactants will be reacted in this Paper and Black marker – These will be used to carry out the disappearing cross method
Method:
- I will gather up the listed equipment.
- I will draw a cross on the paper using a black marker. This will be used in each experiment.
- I will measure the volume of the Sodium thiosulphate to 45cm3 using a measuring cylinder and this will not be diluted.
- I will then pour this into a conical flask that will be placed on the cross I drew earlier and it will also contain the 5cm3 of hydrochloric acid.
- I will start timing the reaction using a stopwatch at the moment I pour the Sodium thiosulphate into the hydrochloric acid.
- I will stop timing when the cross can no longer be seen as the precipitate has formed making the cross obscure. I will record the results in a table.
- The experiment will be repeated 5 times for different concentrations of sodium thiosulphate by decreasing its volume in 5ml increments. The Volume of distilled water will be increased in 5ml increments thus diluting the hydrochloric acid.
Below from the table you can see how I will vary the concentrations.
Diagram:
The diagram shows what your equipment should look like once you have set it up.
Safety:
Goggles and an apron should be worn at all times because I will be dealing with corrosive chemicals e.g. HCL. The taps from which the distilled water will be tapped off from should be closed after use to make sure no one slips and falls sue to a spillage. The corrosive chemicals should be poured carefully so no spillages again can occur.
Results:
I carried out my experiments twice and as well as my own results I used another person’s results to have a bigger range of results therefore a greater accuracy and then I have also made averages (means) for the sets of results by adding them together and dividing by 3. In the table below the times are only shown from each experiment, if you want to see the concentrations used see the method.
Evaluation:
Overall, my experiment worked very well. I believe that my results and my graph were accurate enough to enable me to create suitable conclusions.
No anomalies took place in my experiments; this is clearly shown as the points on my graph are either close to the line of best fit or on it. One point on the graph that was my last experiment was slightly away from the line of best fit, but it did support the trend. The reason why this was slightly out could be explained by a number of factors. A problem with the equipment used was the plastic measuring cylinders. These measuring cylinders were particularly hard to read and also due to them being translucent, it made it even more difficult to read off. Instead of the use of plastic measuring cylinders could be replacing them with more accurate and transparent glass measuring cylinders, which are easier to read off.
Problems in the method were determining when the reaction was over. The reaction was over when the cross at the bottom of the conical flask was no longer visible however it was at times hard to determine this, as the cross could still be slightly visible, but the watch may have been stopped. Another problem that occurred was when a looking directly over the conical flask to check the visibility of the cross a harmful gas was given off so it was hard to look for too long so this could affected the accuracy of the results.
A solution to these problems is to use better, more suitable equipment. To determine when the reaction was over and the cross was no longer visible; using a light sensor, which passes a light beam through the conical flask where the reaction between sodium thiosulphate and HCl is taking place, could do this. The beam of light would go vertically down the conical flask and travel through the solution in the flask. A stopwatch would start as soon as the light beam has passed through the solution and when no more light can pass through the cloudy solution the stopwatch will stop. From this the result can be recorded and due to light being so fast the results would be very accurate and reliable.
The results obtained in the investigation were reliable as the results that I obtained were consistent with each other. The information that I also obtained could also be justified through the collision theory, in that the rate of reaction would increase as a result of more random collisions taking place and an increase in chance that reactant molecules would have enough activation energy.
Some other experiments I could do to further my investigation could be to extend the range of the concentrations I used. Having more results would enable me to spot a better trend or pattern. Below you can see the table of the extended concentrations I could use again keep the total volume of the reactants the same.
