Sodium Thiosulphate + Hydrochloric Acid
Na2S2O3 (aq) + 2HCL (aq)
For my preliminary investigation I used the variable concentration to give me an idea of the range of results and what to expect in my final investigation. The study produced the following results:
These results have given me an idea of how far the range will vary and that if you do the experiment a number of times the results don’t drastically change.
This is the list of apparatus that I needed to carry out the preliminary investigation:
Beaker - Where both the Sodium Thiosulphate and the Hydrochloric Acid will be poured and react.
Burette - Contains the Sodium Thiosulphate, Hydrochloric Acid and water are contained practically (measures accurately).
Test tubes - To contain all the different concentrations of Sodium Thiosulphate.
Test tube rack - To stably hold all of the test tubes upright.
Water bath - To keep the temperature of all of the different concentrations at a constant to maintain this variable.
Paper with cross on - Placed under where the reaction takes place (beaker)
Stopwatch - Used to time the rate of reaction.
Method for final investigation:
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First of all I measured out the amount of Sodium Thiosulphate that was needed e.g. 25cm3, 20cm3 etc from the burette into a test tube
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Next measure out the amount of water that was needed e.g. 5cm3, 10cm3 etc from the burette into a test tube.
- Put both of the test tubes into a test tube rack.
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Put the test tube rack into the water bath at a temperature of 40oC so the temperature doesn’t affect the results as it is also a variable.
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Wait ten minutes to insure that both of the substances are at 40oC.
- Next take both of the substances out and put the beaker on top of the cross on a piece of paper, pour both the water and the Sodium Thiosulphate into the beaker.
- Start the stopwatch once you have poured in both substances.
- Look straight down the top of the beaker and you should be able to see the cross, you should stop the stopwatch when the substance becomes so cloudy that you can no longer see the cross.
You should repeat this experiment for each of the concentrations that are needed varying the water and sodium Thiosulphate as you go.
Diagram of experiment:
My prediction
If the concentration of a solution is increased there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other. Therefore the lower the concentration gets the longer it will take for the equal amount of reaction to take place.
Chemistry Results
Explanation of outlier: I believe that this is a result of human error this could have been caused by me adding more water than I expected or meant to. If this was the case this would have affected the results directly. Therefore as there was a considerable difference between this result and the other two results of the same concentration I have decided to remove this from my results and this will not be included in my graph.
Chemistry Evaluation
In my final experiment I have found that as the concentration decreases the time taken for the reaction to take place increases. This also means that the higher the concentration more reactions will therefore occur.
Using the graphs, with lines of best fit, I can draw a conclusion from my investigation. It shows me that it fits my prediction because as the concentration decreases the time taken for the reaction to occur increases. I believe this is the case because when solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. As the experiment went on the higher concentrations proved to have small increases in the amount taken in seconds such as four seconds. When the concentration got weaker there where big jumps such as doubling on average in seconds from 10cm3 to 5cm3 of Sodium Thiosulphate.
For this to fully make sense it is necessary to recap the collision theory briefly:
For a reaction to occur particles have to collide with each other. Only a small percentage of results in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. If the frequency of collisions is increased the rate of reaction will increase. However the percentage of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration.
So from the evidence I have collected from my investigation I can tell you that I had one outlier throughout my investigation but it was clear and so easily noticed and sufficiently removed. It is clear to me that the rest of my results are accurate as I have done three tests for each concentration this shows me that there was not to bigger range between results of the same category which assures me my results are accurate.
Overall I feel that I have conducted a reliable and fair investigation. If I where to do this experiment again I would use a measuring cylinder as well as a burette to insure even more accuracy and sustain an experiment with no outliers.
