I am going to investigate the factors that affect the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

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Key Stage 4 Science 1 Assessment

Investigating Rate of Reaction

Plan

I am going to investigate the factors that affect the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid. These two react together according to the equation bellow:

SodiumHydrochloricSodiumWaterSulphur

ThiosulphateAcidChlorideDioxide

Sulphur

aSClaClSS

The factors which I could investigate and that have an effect on the rate of reaction are volumes of solutions, density, temperature, concentration, the way in which you are going to view and record the rate of reaction i.e. from what angle/side and the last factor which would affect reaction is different ways of stirring the solution.

The factor, which I will choose to change, is the concentration of solution.

To help me carry out my main experiment, I am going to base it on my preliminary experiment. From the results of my previous experiment, I can make a prediction fro the one I'm doing now. On my preliminary I did five readings and that worked fine, but I thought that if I did it six times, I would have had a more accurate reading. Each time I was either increasing or decreasing the factors by 5, so this time I will do the same again because I think that worked.

Having chosen the factor I am going to predict that as the concentration Sodium Thiosulphate increases, the time taken for the reaction decreases, which means that rate of reaction increases. I think this was because the increase in molarities means more solute in the same amount of solvent. Increasing this, increases the collision frequency and hence the rate of reaction.

To make sure my experiment is a fair test I will keep the volume of solution constant. The colour change and density of what is being obscured will stay the same, too. When I am judging the cross disappearing, I will first decide where I am going to view this from and keep that the same too. The amount of times I stir the solution and with what strength will have an affect on the rate, so I will try to keep that constant. As I am doing the experiment at room temperature, I cannot really control it so I would hope it stays the same as that can have a big effect on the readings.

In this experiment I am going to observe the colour change when all the reactants have been added together, and the rate of reaction as it happens. I will use a cross to make it easier to note down the readings I get and it will also make it more accurate for me as to when to start and stop the stop-clock. I will take six measurements, because I think it will give me a better idea and result of the rate it’s going at. I've selected this number because of my preliminary experiment. The previous time it was five and that worked fine but six would be better.

Method

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        First I will get all the solutions I would need for this experiment like Sodium Thiosulphate and Hydrochloric Acid, so I don’t waste my time looking for it afterwards. Then I would get all the apparatus, which is required for the experiment like conical flask, measuring cylinder and test tubes. I will also have my safety goggles on me just incase something might happen. Next I will measure the amounts of each of the solutions.

As you can see I am going to keep Hydrochloric Acid at constant volume but change the amounts of Sodium Thiosulphate, which will ...

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