The effects of change in concentration on the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

Topics: Chemical reaction, Reaction rate, Chemical kinetics Pages: 11 (1753 words) Published: May 13, 2005

PLANNING: Skill Area P

Write down the aim of your Investigation.

To investigate the effects of change in concentration on the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

Briefly describe your Preliminary Experiment and include your results. Explain how these results have helped you plan your main experiment (p8b).

An increase in concentration will lead to an increase in the rate of reaction because there will be a greater number of particles per unit/cm3. The particles will be closer together and have greater chance of colliding and therefore reacting. The activation energy barrier is more likely to be overcome when particle with greater energy react therefore collisions are more likely to occur. This can be justified by relating to the Collision theory, which is that '...before we can get a chemical reaction, particles must crash together...' with enough energy. Molecules exceeding the activation energy collide together to initiate the reaction. They must be also correctly orientated in order to successfully collide. This means that the graph drawn up in my analysis will have a negative correlation, because as one variable increases the other one decreases. In this case as concentration increases the time taken for the reaction to occur will decrease. The graph shown below is taken from my preliminary experiment's results and supports this argument.

Volume of

dilute HCl(cm3) Volume of 40g/dm3

Sodium Thiosulphate Volume of

Water(cm3) Time taken for Cross

to disappear(sec)

5 50 0 31

5 40 10 39

5 30 20 52

5 20 30 55

5 10 40 89

List all the apparatus that you now plan to use (diagrams should be included) (P4b).

Based upon my preliminary experiments I decided on using the following apparatus:

x1 stopwatch

x1 thermometer

x2 measuring cylinders

x1 conical flask

x1 beaker

x1 X board

x1 pair of goggles

x1 apron

240cm3 of hydrochloric acid

900cm3 of sodium thiosulphate

1500cm3 of distilled water

Describe the method you plan to use, include all safety precautions (p4a)

1. 110cm3 of sodium thiosulphate solution will be used each time, but at varying degrees of concentration. The first solution then, will compromise 10cm3 of 40g/dm3 sodium thiosulphate, which in a conical flask, and then 100cm3 of water will be added to complete the solution. 10cm3 of dilute hydrochloric acid will be poured into a separate measuring cylinder.

2. The flask is placed on the X board. The acid is poured into the flask which has the sodium thiosulphate solution in it.

3. As the hydrochloric acid mixes with the sodium thiosulphate and the water in the flask, the stopwatch is started. The flask is viewed from the top and then as the cross disappears the stopwatch is stopped and the time recorded.

4. These steps are to be repeated but the concentration of sodium thiosulphate will be varied. This will be done by mixing different volumes of the original sodium thiosulphate solution with water.

5. The whole procedure is repeated twice more and an average value calculated. The average will give a good summary of results for the experiment. It will also make the results more credible, removing any possibility of a coincidence and will assist in reaching a conclusion.


-All the apparatus particularly acids and other solution will be kept away from the edge of the bench.

-Aprons will be needed to protect the skin and uniforms.

-Goggles will be used to protect the eyes.

Write down the factor you are going to vary and say how you will do this (P6b).

The factor, which is going to be varied, is the concentration of sodium thiosulphate. This will be done by adding various quantities of water to the solution to produce various concentrations.

Write down the factors you want to control or monitor (P6a).

The factors I am going to control are:

-temperature (room temperature)...
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