Experiment 3 is to decide on the concentration intervals to see if the results have any correlation between them.
For my experiment I will need the following apparatus:
- 3 measuring cylinders (50ml)
- Thermometer
- Conical flask
- Safety goggles
- Stock watch
- A piece of paper with maker on
- Solutions of hydrochloric acid and sodium thiosulphate
- Water
- I will measure all the solutions for each experiment using a 50ml measuring cylinder. For each solution I am going to use a separate measuring cylinder so that separate solutions do not get mixed up before the experiment as this can affect the results.
- I will then put a piece of paper with an “X” marked on it underneath my conical flask. I will use the same marker for all my experiments, the marker will be printed off on the computer because it is more accurate this way as the printing is even but if the “X” is written on in pen the darkness of the pen may not be even.
- I will pour all the solutions into the conical flask and start my stop watch. I will use the same conical flask for all my experiments but I will rinse it thoroughly after an experiment at least 3 times.
- I will then give my conical flask a gentle shake to help the solutions mix together properly. I will repeat this with all my other experiments for a fair test.
- Then I will put a thermometer in to my conical flask and measure the temperature for each experiment. I am doing this because this would help me explain any anomalies found in my experiments.
- When I cannot see the marker through the conical flask I will stop my clock watch. I will use the same person to measure when they cannot see the marker through the solution.
- I will repeat these procedures for all my experiments but change the concentration of sodium thiosulphate diluted with water for each experiment.
Safety precautions
- When I am conducting my experiment I will wear safety goggles in case I get hydrochloric acid or dangerous solutions in my eye
- I will keep paper towels near my experiment to wipe up any spillages immediately if there are accidents
- I should not run in the science lab and especially if I have test tubes in my hands
- My hair should be tied back because it is long. If it is not it could block my vision when I am pouring dangerous solutions and cause spillages
- Bags and coats and stools should be under the table when conducting the experiment so that people passing by don’t trip on them.
- I will also be standing up when I conduct my experiment so I can avoid accidents such as spillages quickly
- The table I am conducting my experiment on must be clear and have enough space to hold my apparatus so that it doesn’t accidentally get knocked off my table.
- I will take care when pouring solutions into measuring cylinders because I do not want my skin to come into contact with it. But if it does I should rinse my skin in cold water.
Fair test
In this experiment my independent variable is the concentration of sodium thiosulphate. I will be changing the concentration of this by diluting the solution with water. I am changing the concentration of sodium thiosulphate because from my preliminary experiments I have found that changing the concentration of hydrochloric acid does not affect the rate of reaction greatly.
My dependent variable is the rate of reaction and the hydrochloric acid used.
My controls are:
Temperature; the temperature affects the rate of reaction as the reaction is faster at a higher temperature. In order to keep the temperature the same I will leave my solutions in the room before the experiment for 2 hours so they can adjust to room temperature.
Same conical flask used; this is so that it is a fair test so I can compare the result with the results from other experiments conducted in the same conical flask.
The solution of hydrochloric acid will have to be a 2M solution and the sodium thiosulphate will have to be a 0.05M solution or else it won’t be a fair test because a larger molar solution would contain more reactant particles because it is more concentrated and this would affect the rate of reaction which in turn affects my experiment results.
For a fair test I also have to use separate measuring cylinders to measure out each of my solutions because this might affect my results e.g. if I used the same measuring cylinder to measure hydrochloric acid and then sodium thiosulphate the sodium thiosulphate solution would start reacting with the remains of hydrochloric acid before my experiment even starts so this would affect my result.
The marker I use will also have to be same for a fair test and the same person for deciding when they cannot see the marker will have to remain the same for a fair test because various people have different opinions on when they cannot see the marker. The thermometer used will have to be kept the same as well to make it a fair test.
Measurements
The measuring apparatus I am using are:
Measuring cylinder
Stop watch
Thermometer
The measuring cylinders I am using only needs to hold 50ml the most and this is very accurate. For a more accurate measuring cylinder I could use a 25ml measuring cylinder. I am going to use the 25ml cylinder to measure out my solutions because this is more accurate than the 50ml measuring cylinder.
The stop watch I am using is very accurate and reliable. It can measure to a 100th of a second, but for my experiment the results do not require that degree of accuracy so I am just going to use minutes and seconds for my time measurements. But I am going to use the stop watch as it is accurate and simple to use.
The thermometer I am going to use is quite accurate as it measures to the accuracy of one decimal point. This is required for my experiment for the most accurate results so I am going to use this thermometer.
Before I conduct my experiment I will conduct three preliminary experiments.
The first preliminary experiment is to find out which solution greatly affects the rate of reaction
The second preliminary experiment is to decide which concentration of solutions to start with.
The third preliminary experiment
My preliminary results were as follows
Experiment one results:
Results of experiment when I changed the concentration of hydrochloric acid in solution:
Results of experiment when I changed the concentration of sodium thiosulphate in solution:
The results from preliminary experiment one tells me that sodium thiosulphate affects the rate of reaction greatly so for my practical experiment I will be changing the concentration of sodium thiosulphate in the solution.
Experiment two results:
For experiment two I am going to decide which concentration of sodium thiosulphate I am going to start with. The results are as follows:
From the results I can see that I need to start my practical experiment with a concentration higher than 20ml of sodium thiosulphate because the reaction was very slow and quite time consuming.
Experiment three results:
For experiment three I am going to decide what concentration intervals I should use for my practical experiment because if the concentration of sodium thiosulphate is too weak then it would be too time consuming because the time I have for my practical experiment is limited.
The results are as follows:
I am quite happy with the results from preliminary experiment number three as there are no anomalies within my results because they all seem to follow a general patter; as the concentration of sodium thiosulphate in the solution increases the time taken for the marker to disappear decreases.
I am quite happy with the concentration intervals as they are not too time consuming and they can all be done within the time I am given for my practical experiment.
I am going to keep these concentration intervals for my practical experiment because it is practical and also it can be much better for comparison with the results from my preliminary experiment if anomalies occur.
My prediction
I predict that as the concentration of sodium thiosulphate mixed with water increases the rate of reaction increases when it is reacting with hydrochloric acid.
This is because there are more particles of reactants in sodium thiosulphate when the solution is more concentrated. This increases the chance of a successful collision with the reactant particles of hydrochloric acid as there are more reactant particles involved.
A more concentrated solution of a reactant also possesses more energy so the atoms are moving at a much faster rate and therefore increasing the chance of a successful collision. This also increases the rate of a successful collision as the reactant particles possess more energy.
A successful collision is when the reactant particles collide into each other and react to form a new product. If the reactant particles do not possess enough activation energy then a new product will not be formed even if they do collide.
I predict that as the concentration sodium thiosulphate increases the rate of reaction with hydrochloric increases at a proportional rate, I predict that as the concentration is doubled the reaction rate is doubled as well. I predict this because if the concentration of a solution is doubled then you have twice the number of reactant particles therefore the reaction rate should be twice as fast.
I predict that the graph will show
Positive correlation like the one shown in this graph and it will be a linear relationship.
Results
In order to get the most accurate results as possible I am going to repeat my experiment three times and take the average time for each experiment.
I will also calculate the concentration of sodium thiosulphate, hydrochloric acid by using the formula:
Volume of chemical × molar of solution
Volume of solution
My results are as follows:
Results from my practical:
My results were quite reliable as all the times were with in 5% of each other. This is very accurate and reliable.
My results also showed a pattern that emerged which matched my prediction. From the results I can see that as the concentration of sodium thiosulphate increases the reaction rate increases as well, this proves my prediction because of the collision theory.
I worked out the rate of reaction by using the formula:
________________1_____________________
Time taken for cross to disappear in seconds
I am now going to draw a line graph showing the relationship between the rate of reaction and the concentration of sodium thiosulphate, I will also add a line of best fit in my graph to see if there is a positive correlation as this will prove my prediction as right.
I will draw my graph by hand to make the scale as clear as possible for the most accurate results.
From my graph I can tell that there is a clear positive correlation between the concentration of sodium thiosulphate and the rate of reaction. The points on my graph also fitted my line of best fit very well however there was one anomaly.
The rate of reaction for the 0.045M solution of sodium thiosulphate was too fast compared to the line of best fit.
This could be due to a number of factors such as a higher temperature or human error because it is often quite hard to decide when the cross disappears completely.
I am going to use the results from the graph to see if my prediction “as the concentration doubles the rate of reaction doubles” is right.
In order to do this I will find the rate of reaction for a concentration and find the rate of reaction for double the concentration using my results and the line of best fit in my graph.
From my graph and the line of best fit I can see that my prediction “as the concentration doubles the rate of reaction doubles” is right. As the table of results from my graph shows that as the concentration of sodium thiosulphate doubles the rate of reaction doubles. My results were fairly accurate as they are all very close to the line of best fit and match my prediction.
This shows that my prediction is right because using my results from the graph and the line of best fit I have calculated that the rate of reaction doubles when the concentration of sodium thiosulphate is doubled.
This is because as the concentration of sodium thiosulphate doubles there are double the number of particles of sodium thiosulphate; this doubles the chances of a successful collision between sodium thiosulphate particles and hydrochloric acid so therefore the reaction rate is doubled.
My results agree with my prediction because using the graph of my results I can compare the rate of reaction for a certain concentration and then compare the rate of reaction for double the concentration of sodium thiosulphate used.
My results show me a clear trend that as the concentration is doubled the reaction rate is roughly doubled. My results showed very strong correlation of this.
However the results from my practical took place faster than my preliminary results for the 0.025M, 0.03M reactions with hydrochloric acid, this is because my practical experiment was carried out at 17 degrees and my preliminary was carried out at 16 degrees. It is hard to control the room temperature so nothing could be done about it.
However some of my results were calculated using my line of best fit, I used my line of best fit to calculate the rate of reaction for the 0.01M, 0.02M and 0.015M concentrations of sodium thiosulphate; this should be quite accurate as my results were very good and showed very strong correlation. They also fitted the line of best fit quite well.
Evaluating evidence
The experiment worked very well, looking at my results everything went well and my results were fairly accurate as they were all within 5% of each other and the results all fit the line of best fit quite close in my graph.
The results also show a very good positive correlation and a definite trend that as the concentration of sodium thiosulphate increases the rate of reaction also increases.
However I did have one anomaly in my results that did not fit the line of best fit very well. The rate of reaction for my 0.045M solution of sodium thiosulphate was 4.2 × 10-3 when it was predicted by my line of best fit to be 3.85 × 10-3. This could be due to a number of factors such as the experiment was done at a higher temperature or there was some hydrochloric acid mixed with some sodium thiosulphate before the experiment in a measuring cylinder or just human error because it is quite hard to judge exactly when the cross disappears.
However it could not have been due to temperature because I measured the temperature for each one of my experiments and they were all carried out at 17 degrees. I also took precautions to make sure that no hydrochloric acid ever came into contact with sodium thiosulphate as I used separate measuring cylinders for each reactant and after using the same conical flask for experiments I rinsed it thoroughly with water at least three times.
So I think my anomaly is due to human error because it is hard to tell when the cross has completely disappeared and different people have different opinions on that which may cause different results.
I think my method is quite reliable and I did everything I could to make it a fair test. The temperature is hard to control but all the experiments were carried out at room temperature in the same room and I measured the temperature of all of my experiments and they were carried out at 17 degrees so this was a fair test.
However in order to make my experiment better I could use a mechanical way to measure when the cross cannot be seen anymore; this would decrease the chances of human error, be a better fair test and also be more accurate.
In order to do this I could use a special light measuring device. Light could be shone through the conical flask and beneath it a light receiver with a reading could be placed. I could see how long it takes for the reading on the light receiver to go down to a certain number. This would ensure a fair test and rule out chances of human error because this machine is designed to measure light and be accurate. This would also make my results more reliable. The piece of apparatus I would use would be a light gate because this is especially designed to sense light.
My results are quite reliable because I have taken all the precautions to make it a fair test and my results are very accurate as the results were all within 5% of each other which shows consistence and it also matches my prediction very well.
However the results for the 0.01, 0.02 and 0.015 molar concentration of sodium thiosulphate were predicted using my line of best fit on my graph but I think the line of best fit is reliable because my results were very good and show very strong positive correlation. I also repeated each of my experiments three times to make the results as accurate as possible. My only anomaly was the 0.045M concentration of sodium thiosulphate, the rate of reaction was too fast compared to my line of best fit. I think this is due to human error as it is hard to tell when the cross disappears. All my practical experiments were carried out under the same circumstances and all at room temperature so the change in the rate of reaction cannot be due to temperature.
In order to extend my experiment I could use 12 different concentrations of sodium thiosulphate instead of the 6 I used for a more accurate result.
The graph could also be dawn on the computer using Excel so the correlation could be calculated to see how good the correlation is.
In conclusion my prediction was right; the rate of reaction doubles between hydrochloric acid and sodium thiosulphate when the concentration of sodium thiosulphate doubles. This is because there are double the numbers of reactant particles of sodium thiosulphate so this increases the chances of a successful collision.
