Stopwatch: This is used to measure how long it takes for the cross beneath the solution to be unnoticeable.
Equations
If my experiment is successful then this is the reaction that will take place:
Sodium + Hydrochloric Sulphur + Sulphur + Sodium + Water
Thiosulphate Acid Dioxide Chloride
Na2S2O3 (aq) + Hcl (aq) S (s) + SO2 + NaCl (aq) + H2O (l)
Variables
These are the variables for this experiment:
Controlling the key variables and fair test
To make this a fair test I must control the key variables. We must keep the cross on the piece of paper in the same place so as not to loose it. If we were to use a different cross each time then the experiment would not be fair because the cross could be of a different size and shape making it harder or easier to see through the solution. In the same way we must ensure the use of the same apparatus so that thee test is fair.
To do the experiment with the same surrounding environment I will do the experiment in the same room each time. This will not ensure that the environment is the same each time but will ensure that it is similar.
During the experiment there will be a margin of human error when watching the solution and using the stopwatch. So, to minimise this error we will use the same person to judge the visibility of the cross and use the stopwatch each time.
To make sure that the experiment is fair, we will have to use the same concentration and volume of solution each time so that we are only changing one variable. To do this we will have to use the same person to measure the solution for each experiment. This [again] will minimise the human error in measuring.
To make this test fair we will do the experiment a total of 3 times. This will hopefully rule out any anomalous results.
Method
To carry out this experiment I am going to, firstly, collect the apparatus listed above. Once I have the equipment I will set it up as shown below [being careful to measure the quantities of the solution accurately] and I will heat the Sodium Thiosulphate solution slowly until the thermometer reads the temperature intended. Once it is successfully heated It will be placed on the piece of paper with the cross drawn on it and then the Hydrochloric acid will be added. As soon as it is added the stopwatch will be started. I will then observe the solution and stop the stopwatch when I can no longer see the cross beneath it. The time of this will be recorded for all temperatures within the range 30°C to 60°C [Going up progressively in steps of 5°C]. The experiment will be completed a total of 3 times to ensure that it is a fair test. Once I have carried this out I will analyse my results and draw a conclusion.
Diagram
This is how I will set up the apparatus:
Safety
To ensure total safety during this experiment I will wear safety goggles at all times. This will prevent potentially hazardous materials from entering my eyes. I will also tuck my school tie into my shirt. By doing this I will minimise the risk of it flapping around and lighting on the Bunsen burner. Another safety precaution that must be taken is being very careful when pouring the irritant or corrosive liquids into the measuring cylinder. Failure to do so could result in inflicting serious harm on others or myself. When I am not using the Bunsen burner it will always be on the safety flame to stop possible injury by serious burns.
Range of data to be collected
In this experiment I will be collecting a total of 63 pieces of data. This is what I will record for each temperature that I use:
- Temperature: - Actual temperature for experiment 1
- Actual temperature for experiment 2
- Actual temperature for experiment 3
- Average actual temperature.
I am going to record my actual temperature for every experiment because I will have a target temperature that I hope to reach but this may not always be achievable because of human error. So recording the actual temperature will give more accurate results when it comes to plotting my graph and analysing my results.
- Time taken for the cross to become not viewable: - Time for experiment 1
- Time for experiment 2
- Time for experiment 3
- Average time
I have repeated the experiment to try to rule out any anomalous results [as mentioned in the fair test].
- The rate of the reaction:
The rate of the reaction can be found using the following formula: 1/s
This is equivalent to: s-1
This means 1 divided by the time in seconds.
Because I am doing the experiment for a total of 7 different target temperatures [30°C, 35°C, 40°C, 45°C, 50°C, 55°C and 60 °C] there will be a total of 63 pieces of data to collect. There are nine results to obtain for each temperature [above].
Preliminary experiment
I carried out a preliminary experiment for my planned experiment. I did this to test that it worked correctly and that the values of temperature and concentration worked well. To do this experiment I simply used to highest and lowest temperatures to test the range of my values. These are my results.
Upon completing this preliminary experiment I realised that the reaction was occurring too quickly for the measurements to be taken accurately. So I realised that I can do one of two things: Change the concentration of my Sodium Thiosulphate solution or change the temperatures that I used. I decided to change the concentration.
I will now use a ratio of 2:3 [two parts Sodium Thiosulphate solution to 3 parts water] whereas before I used a ratio of 3:2.
I performed another preliminary experiment to try this. These were my results:
I also decided that was too fast to record accurate results so I changed the ratio again. This time I changed it to 1:4.
These were my results:
After doing this I decided that this was a good concentration of the solution to use because it takes a reasonable amount of time to allow for more human error without being too long or too short. So the ratio of Sodium Thiosulphate solution to water that I will use will be 1:4.
Obtaining
Results
Here are the results for my experiment:
Analysis
Numerical methods
To interpret the results previously I have used two calculations; these are obtaining the mean and the rate of the reaction. This is why I have used these:
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Mean [average]: I needed this calculation to obtain an average of the time and actual temperature in this reaction. This converts each repeat into a single figure which can be easily plotted on a graph and hopefully rules out anomalous results.
-
Rate: This is a simple calculation [described in the “Range of data to be collected” section] which determines the rate of the reaction. Rate is defined as 1/s or S-1.
Graphical analysis
To help analyse my results I will draw a graph. The graph will show the correlation between the input and output variables and will be an effective and easy way to compare the results to my prediction. I will use an X/Y graph with a line of best fit to do this. My reason for doing this is it will be very easy to spot a trend from and will be a good aid in helping me draw a conclusion.
[Please turn to next page to see the graph]
Trends observed in the results
If you look at the graph above you will notice that as the temperature increases so does the Rate of the reaction. The variables, therefore, have a positive correlation. This implies that temperature acts as a type of catalyst that can be used to speed up certain reactions.
You may also notice that the rate increases higher at higher temperatures than at low temperature.
Conclusion
Based upon my observations from my experiment my scientific knowledge I can conclude that the higher the temperature then high the rate of the reaction. This means that Temperature can be used to speed up or slow down a reaction.
Scientific knowledge behind my conclusion
I based my conclusion up the collision theory: “For a reaction to successfully take place the particles must collide with one another”. My results showed that as the temperature increased so did the rate of the reaction. This is because temperature causes the particles move and a higher temperature causes them to move faster thus resulting in a higher chance of successful collision occurring. This temperature also causes the particles to have more energy and therefore when they do collide do so with a much greater force and result in a stronger/faster reaction.
My scientific knowledge agrees with my conclusion.
Comparison of conclusion with prediction
My prediction stated:
“I believe that as the temperature increases so will the rate of the reaction. I think that if you double the temperature the rate will also double and therefore the two are relative.”
My conclusion agrees with the first part of my prediction but not the latter. This is because the graph is not a straight-line graph and does not increase at the same rate throughout. This also means that my graphical prediction was incorrect as it shows a straight line but the results show a curve. I believe this is because as the temperature increases it keeps adding more and more energy to the particles resulting in a significantly higher rate for high temperatures than low temperatures.
My conclusion does agree with the opening statement of my prediction though as it is now proven that as the temperature increases so does the rate of the reaction.
Evaluation
Quality of my results
My results are of good quality. This is because:
- My results showed a strong correlation.
- The repeats were all very similar showing little variation. This shows consistency and a definite trend.
- There were no anomalous results. All results followed the trend.
Quality of the experiment
I believe that I carried out this experiment well. The only problems were:
- It is difficult to judge when the cross is no longer visible accurately every time.
- Sometimes when observing the cross, the conical flask had condensation inside it after heating the solution. This may have obscured our vision of the cross.
My experiment all worked as planned and I believe that if I took more repeats then the results would have more accuracy.
Was my evidence good enough to support my conclusion?
I believe that my evidence was satisfactory to support my conclusion as it showed a highly strong correlation and accurately followed my prediction. Although, it could have been improved by doing more repeats [as stated above].
Further Investigations
To investigate this further I could change the input variable to the concentration of the Sodium Thiosulphate Solution and investigate the relationship between this and the rate of the reaction.
This is a brief insight into what I would do:
Aim
The aim of my experiment is to investigate the relationship between the concentration of a solution and rate of reaction. In this case it will be a reaction between Hydrochloric Acid and Sodium Thiosulphate.
Hypothesis
If I were to carry out this experiment I believe that as the concentration of the solution increases so will the rate of the reaction. I also believe that if I were to draw a graph of the results it would look like this: [following page]
I think that it would look like this because I believe that the rate of concentration will have the same effect on the experiment as the temperature.
Scientific knowledge to back up my hypothesis
I believe my hypothesis to be correct because of my scientific knowledge prior to the experiment. We know that for a chemical reaction to occur particles from the two chemicals need to collide. This is called the ‘collision theory’. This means that for the reaction to be successful the particles must collide and react with one another. My hypothesis “I believe that as the concentration of the solution increases so will the rate of the reaction” is based on my knowledge that if you use a stronger Sodium Thiosulphate solution then there will be more Sodium Thiosulphate particles in the solution. This means that there will be more particles to collide with the Hydrochloric Acid particles, resulting in a faster reaction.
Method
My experiment will be carried out in a very similar way to my original experiment: All of the apparatus will be collected and set up. Once this is complete I will pour the Hydrochloric Acid into the conical flask containing the Sodium Thiosulphate solution and measure the time taken for the cross to be unnoticeable beneath the mixture. Once this is complete I will repeat the experiment with different concentrations of Sodium Thiosulphate by using different ratios of Sodium Thiosulphate : Water. The experiment will be done a total of 3 times for accuracy and fair testing. Once all of the results are recorded I will draw a suitable conclusion.
By Dave Bennett
11F0
