Sodium Thiosulphate Investigation
To investigate how the concentration of hydrochloric acid affect the
rate of reaction.
Sodium Thiosulphate reacts with hydrochloric acid to form a yellow
precipitate. The word equation for this is :
Sodium Thiosulphate + Hydrochloric acid = Sodium Chloride + Sulphur +
The chemical equation for this would be Na2S2O3 + 2HCl = 2Nacl + S + H2O
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.
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
1 Conical Flask
2 Measuring Cylinders
1 Small Piece Of Paper
- A 'x' was marked on the piece of paper with a pen
- 20 cm3 of sodium thiosulphate was then poured into the measuring
cylinder from the beaker
- 10 cm3 of hydrochloric acid was poured into the measuring cylinder
- The conical flask was then put onto the piece of paper marked with
- The sodium thiosulphate and the hydrochloric acid were then poured
into the conical flask at the same time
- A stopwatch was then used to time the reaction and see how long it
took for the solution to turn yellow until you...