The preliminary work shows that the reaction between sodium thiosulphate and hydrochloric acid results in product of chloride, water, sulphur dioxide and Sulphur. This experiment will aid me to investigate my objective by me timing the take taken for the reaction to occur and for me to not be able to see the cross underneath the beaker. Since I am investigating the factors of concentration and its affects on rate of reaction, I will change the concentration of the solutions used for my experiment and take the time it requires for me to not be able to see the cross.
Prediction
In this experiment I predict that as the concentration of either solutions is diluted, the rate of reaction will decrease, this is because there will be less reactant particles present in one of the solution, therefore less successful collisions will take place. Here is a sketch diagram showing the relationship between the rate of reaction and the concentration.
- Concentration of sodium thiosulphate is low, therefore rate of reaction is slow
- Increase of particles of sodium thiosulphate; therefore more successful collisions and requires less amount of time for reaction
- A lot more particles of sodium thiosulphate are present, therefore rate of reaction is very fast, and the time for reaction is very short
In this experiment I will need to dilute the sodium thiosulphate, this is because I will need to have a variety of concentrations in the experiment so I can investigate on how the rate of reaction is affected by concentration. Also, I cannot change the concentration of hydrochloric acid as much as there are only be 2cm³ in every experiment, while the sodium thiosulphate can have 10cm³ per experiment, therefore giving me more opinions to change the concentration. Below is a table of the concentration I am using for my experiment.
I will measure the time taken for the reaction to take effect and stop the time when you are unable to see the cross; this shows the rate of reaction, and this can be used to contrast with the concentration of solutions in a graph shown previously.
Apparatus list
Below is a list of the apparatus needed for my experiment:
- Sodium thiosulphate solution- used for part of the chemical reaction
- Hydrochloric Acid solution- used for part of the chemical reaction
- Distilled Water- used to dilute the concentration of sodium thiosulphate
- Measuring cylinders- used to measure amount of solutions needed for each test
- Pipettes- use to intake small amount of solution when necessary
- Beaker- used to contain solutions
- Stopwatch- used to time the time taken for the reaction
- Paper- used for drawing by pen/marker
- Pen/marker- used to draw a cross on the paper
Method
1. collect all apparatus required and set them up in a work station
2. Draw a cross on a piece of paper with a pen/marker
3. Measure the amount of sodium thiosulphate required by using measuring cylinder and pipettes and pour into the beaker
4. Measure the amount of distilled water required by using a measuring cylinder and pipettes and pour into the beaker
5. Place beaker on top of the paper with the cross and get a time watch
6. Measure the amount of hydrochloric acid required and pour into the beaker with the mixture, when the acid is poured, start the timer
7. When you are not able to see the cross underneath the beaker, stop the timer and record results
8. Clean out beaker and apparatus that has been used for solutions and carry on experiment with another concentration
Fair Test and reliability
By following my method, I am able to complete the experiment properly; I will need to do the experiment 3 times as I can then calculate the average and give a reasonable and good result and analysis. In also enables me to ignore any anomalous data that I might have due to certain mistakes that might occur during my experiment. In order to keep this a fair test, I may also wish to have separate measuring cylinders and pipettes for each different solution for my experiment, therefore no reaction will take place in these apparatus when I have mixed and used them, thus giving me an accurate experiment rather than causing anomalous results to appear in my experiment. Similarly, I will need to sort out the lids of the solutions to their right solutions as it can contaminate the solutions and giving me a different/anomalous rate of reaction. I might also need to be aware to stop the time watch when I cannot see the cross from the paper completely rather than stopping the stop watch when the cross is faint, if so, it will affect the results of time taken for each experiment and concentration. If I can keep all variables that might affect my results the same to reduce the chances of anomalous unreliable data.
Safety
To ensure the safety of my experiment, I will need to wear aprons and goggles for protection of my body and eyes from chemical spill. I will need to carry the solutions carefully and work under safe condition without obstructions. When each solution are poured and used, it should be handled carefully and closed completely after it has been used; stopping the risk of chemical spill. If there is a chemical spill stop the experiment immediately and ask for teacher’s assistance, if chemical got onto the eye contact a teacher for advice on use of eye wash.
Observations
I have took accurate reading of the time taken for each experiment by letting each chemical reaction to completely blank out my sight from seeing the cross underneath. I have also followed the advices before on using different measuring apparatus for different solutions to stop reaction taking place early and influencing on the rate of reaction. I did 5 different concentrations of sodium thiosulphate and repeating the experiment 3 times like I have planned. In the following table, it shows the record of my results for each of the experiments.
I have not repeated any of these experiments again due to anomalous results, as they all increase in time taken as the concentration of sodium thiosulphate decreases. Below is a table of the average time taken for the reaction between hydrochloric acid and sodium thiosulphate to occur. I have added all the decimals from each experiments and rounded them up to 1 decimal place after I have worked out the average, thus it will give me an accurate average time rather than rounding the figures up in each experiment, as well as making it easier to plot the graph.
In my graph I have not included the results for 0cm³ concentrations as all the results are at 0, thus giving me an anomalous data to plot of a graph and giving me a weird shape. Below is the graph of the experiment.
Analysis
From the graph, in shows that overall my prediction is correct; as the concentration increases the rate of reaction (time taken) decreases, (i.e. from 173s at concentration 3cm ³ to 24s at concentration 10cm³) This is true because there are more particles in the solutions, thus the chances of successful collisions between two different particles is higher, enabling a faster reaction. Also, I found out that there is no steady gradient as the curve has a steeper gradient between concentration 3cm³ and 5cm³, then the gradient becomes moderate between 5cm³ to 7cm³, and the gradient gets steeper again from 7cm³ to 10cm³. This infers when the concentration increases evenly; it does not give a steady decrease in rate of reaction.
Evaluation
In this experiment I am able to say that my prediction is correct that say confidently that as the concentration of a reactant increases the rate of reaction is faster and required less amount of time to react, this is proven from the graph that I have of my experiment. There were no anomalous results in my experiment as all contributed into my graph. I did not plot concentration Ocm³, even though it gives a correct result, this is because there are no reaction taken place between distilled water and hydrochloric acid, it simply dilutes the solution, therefore it is not necessary to plot its values as it will not help with my analysis on the theory between concentration and rate of reaction.
However, I could not confidently say that my prediction is correct as I might have caused some slightly inaccurate results, which influenced on the gradient and flow of the graph. From the results table, I can see that in each experiment the same concentration required more time to react, this factor might be affected by the way I judged whether I could see the cross/not, this affected the time taken for reactions for each concentrations, thus giving me perhaps inaccurate results, so I could not confirm whether the theory between concentration and rate of reaction is true. There also might have been the contamination of solutions in the beaker after it has been washed for the next concentration/experiment, as washing it in the sink caused water to stay in the beaker, I did not dry the beaker for each experiment, therefore, there might have been slight amount of water already in the beaker; affecting the concentration of the solutions and diluting them. This means the results could have been faster overall for each concentration, therefore suggesting that my results cannot completely confirm my prediction. To improve and make my experiment more reliable, I will need to dry my beaker to stop any contamination between solutions, also taking care of the time taken for each reaction by allowing the reaction to completely stop.
In order to confirm my prediction and statement about concentration and rate of reaction I may do the experiment again but repeating it more than 3 times with more than 5/6 variables for my concentrations, this will allow me to explore in detail of the rate of reaction and giving me an overall conclusion of how concentration affects rate of reaction. I may also do the experiment with different solutions, so that I can confirm whether the rate of reaction between sodium thiosulphate and hydrochloric acid is the same with other solutions. I may also investigate other factors that affects rate of reaction such as temperature to see which factors affects the most to the rate of reaction.
