Investigate how the concentration of sodium thiosulphate solution affects the rate of reaction between it and hydrochloric acid.

Chemistry Coursework – Rate of Reaction

Aim

To investigate how the concentration of sodium thiosulphate solution affects the rate of reaction between it and hydrochloric acid.

Hypothesis

I predict that with an increase in concentration of sodium thiosulphate will come an increase in reaction rate.

I base my prediction on the collision theory, a successful collision being when two particles collide such that they react with one and other.

I have chosen to investigate how concentration affects reaction rate, there are three other aspects which can also effect rate of reaction.

Temperature – The higher the temperature the more energy is gained by particles and so the faster they collide
Particle size (surface area) – The larger the surface area the more exposure to the reactant and so the faster the reaction
Catalysts – A catalyst lowers the activation energy of a substance, meaning particles gain more energy and so move faster, and collide successfully.

All four methods of increasing reaction rate can be explained in terms of increasing the number of collisions.

Apparatus

The equipment I needed was

Varying concentrations of sodium Thiosulphate solution (undiluted concentration at 40 grams/litre)
Hydrochloric acid (2M)
Conical flask
Two measuring cylinders
Piece of paper with a cross drawn on it
Stopwatch
Goggles

Here is an illustration of my equipment:

Method

Place the flask on top of the paper with a cross marked on it
Mix the following concentrations of sodium thiosulphate by diluting the original (40grams/litre) with water.

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All four methods of increasing reaction rate can be explained in terms of increasing the number of collisions.

Apparatus

The equipment I needed was

Varying concentrations of sodium Thiosulphate solution (undiluted concentration at 40 grams/litre)
Hydrochloric acid (2M)
Conical flask
Two measuring cylinders
Piece of paper with a cross drawn on it
Stopwatch
Goggles

Here is an illustration of my equipment:

Method

Place the flask on top of the paper with a cross marked on it
Mix the following concentrations of sodium thiosulphate by diluting the original (40grams/litre) with water.

∙ From the proportions work out how many grams per litre there are in each solution

Pour the first of the above concentrations into the conical flask
Pour 5cm3 of Hydrochloric acid (2M) into the flask with the sodium thiosulphate solution and start the stopwatch
Swirl the mixture gently as you time the reaction
Stop the stopwatch when you are no longer able to see the cross on the piece of paper, as the mixture has become too cloudy

To check the experiment was performed fairly I ensured:

- The volume of hydrochloric acid was always 5cm3

- The temperature was constant

- The experiment was repeated 3 times for each concentration of sodium thiosulphate and an average result taken to improve accuracy.

Trial Run

I chose to do a trial run to test my method. I checked the sodium thiosulphate concentrations 8g/l and 40g/l. I found that 40g/l took 29 seconds to cloud and 8g/l took 4 minutes. This followed the trend I had predicted, (the higher the concentration the faster the reaction) and so made me feel confident about my method.

Results

Analysis

From my graph I can see a trend, the more concentrated the sodium thiosulphate solution the higher the reaction rate, and vise versa. This corresponds with my prediction, which was based on molecule collision theory.

Evaluation

I believe I performed the experiment well and as accurate as I could. I was careful when measuring out the concentrations of sodium thiosulphate and in recording the time. The only result that might be considered an anomalie is the 8g/l solution and those that make up the average. Human error aside however it is likely that this is because there are fewer sodium thiosulphate particles to collide and so the repeat measurements may vary more. If I had the opportunity I might redo the 8g/l concentration to improve accuracy.

The method is simple to follow and I tried to take my time with readings etc to minimise the change of human error. To make it easier to measure out the acid/thiosulphate solution I could use a syringe or large dropper. My results support my prediction so I feel they are reliable, although repeating the experiment more might improve reliability. The only thing I do keep in mind about the results is that they are averages not actual readings.