Investigating the rates of reaction of Sodium thiosulphate and hydrochloric acid

Investigating the rates of reaction of Sodium thiosulphate and hydrochloric acid

Using my preliminary experiments I decided on using the following apparatus: - A conical Flask

- A piece of White Paper marked with a black cross

- Dilute hydrochloric acid

- Sodium thiosulphate

- Water

- Measuring cylinder

We must produce a piece of coursework investigating the rates of reaction, and the effect different changes have on them. The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. It is measured by dividing 1 by the time taken for the reaction to take place. There are four factors which affect the rate of a reaction, according to the collision theory of reacting particles: temperature, concentration (of solution), surface are (of solid reactants), and catalysts. I have chosen to investigate the effect concentration has on a reaction.

This is because concentration is the most practical to investigate as it would take longer to prepare a solid in powdered and unpowdered form, and it is difficult to get accurate readings due to the inevitabilities of human errors, and as gas is mostly colourless it is difficult to gauge a reaction changing the pressure, and if a substance is added to give the gas colour, it may influence the outcome of the experiment.

Also temperature is difficult to sustain and be made exact for all the experiments. Similarly the use of a catalyst complicates things, and if used incorrectly could alter the outcome of the experiment.

All other factors however must be kept constant while we are varying the concentration.

Both the sodium thiosulphate and the Hydrochloric acid are soluble in water, so the concentration of either can be changed. However I have chosen to vary the sodium thiosulphate as it is available in larger amounts, and various concentrations are prepared.

I will time how long it will take varying concentrations of Sodium

Thiosulphate to react with the Hydrochloric acid so that the solution when placed above the white paper with the black cross is so reacted that one cannot see the cross through the opaque liquid.

In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the HCl and thiosulphate will not be mixed up. The amount of HCl will be 5 cm3 each time, and the amount of thiosulphate will be fixed at 20 cm3.

Also room temperature will be used as the temperature as it is practical and will not need to be monitored.