Sodium Thiosulphate Investigation

Sodium Thiosulphate Investigation

Aim:

To investigate how the concentration of hydrochloric acid affect the

rate of reaction.

Background:

Sodium Thiosulphate reacts with hydrochloric acid to form a yellow

precipitate. The word equation for this is :

Sodium Thiosulphate + Hydrochloric acid = Sodium Chloride + Sulphur +

Water

The chemical equation for this would be Na2S2O3 + 2HCl = 2Nacl + S + H2O

+ So2

When dilute hydrochloric acid (colourless) is added to sodium

thiosulphate the solution gradually becomes cloudy as a result of the

solid sulphur. The ’cloudiness’ of the solution increases as the

reaction progresses and more sulphur is formed. Eventually the

precipitate will look quite yellow in colour.

Prediction:

By applying the collision theory, I predict that as you increase the

concentration of hydrochloric acid (HCl), the reaction with sodium

thiosulphate would be faster. However, I also predict that as you

decrease the concentration of HCl, the rate of reaction would be

slower. This is justified by the collision theory. The collision

theory states that for a reaction to happen, particles must collide

with each other. There is a minimum amount of energy which colliding

particles need in order to react with each other. If the colliding

particles have less than this minimum energy then they just bounce off

each other and no reaction occurs. This minimum energy is called the

activation energy. The faster the particles are going, the more energy

they have. Faster moving particles are more likely to react when they

collide. The rate of reaction could be increased by:

1. Raising the temperature.

2. Increasing the concentration (in solution).

3. Increasing the pressure (in gases).

4. Increasing the surface area of a solid.

5. Using a catalyst.

In this case, in order to increase the rate of reaction, we must

increase the concentration of hydrochloric acid. By doing this, it

means that there will be more particles per dm3 of hydrochloric acid.

The more particles of hydrochloric acid in the volume, the closer each

particle will be and the rate of the reaction will increase. The

collision theory is important as it is evidence of how the rate of

reactions work and how it could help to speed up the chemical

reaction.

Method:

Apparatus:

1 Conical Flask

2 Measuring Cylinders

1 Beaker

1 St...

... middle of paper ...

...when the solution turned yellow. I repeated my

results five times. Each set of results were similar, generally the

time between each recording was no more than 4 seconds. This indicates

that my results were quite reliable. My results are reliable enough to

support my conclusion as I had concluded that increasing the

concentration of HCl would lead to a decrease in the time taken to

react. My results show this because the correlation is positive

meaning that it would take longer for a solution to react by

decreasing the concentration of HCl.

If I could improve my method I would use different flasks to pour the

solution in. This is to make sure that there is no residue of sulphur

inside the flask which could affect my results. I would also use a

light sensor to see when the solution turns yellow. By using a line

sensor, it would make it easier to know when to start and stop timing

the reaction. To extend my investigation, I would use different

concentrations of sodium thiosulphate and HCl to see if the reactions

are going to be faster or slower. I would also use different

temperatures for my reactions. This is to see if it will also affect

the rate of reaction.