Investigation Into The factors which Affect The Rate Of Reaction Between Sodium Thiosulphate And Acid

Planning

Plan

        I plan to investigate how the rate of a reaction is effected by a certain ‘reactant increaser’. There are several to choose from : A catalyst, the temperature of one of the reactants, the concentration of a reactant (or when the pressure of the gas increases) and the surface area of a reactant.

        I have decided to investigate the effect of concentration of a reactant. I will do this by using a total volume of acid (50 cm3) and mix it with the same volume of sodium Thiosulphate and measuring how long it takes to produce a certain volume of precipitate. The volume of precipitate will be decided by how long it takes a cross to be non-visible to the human eye. I will place a cross behind a boiling tube and then pour the acid into the sodium thiosulphate  and watch until the cross disappears from my sight (when  a certain amount of precipitate has been produced). I will time how long this take and record my results in a table. I will repeat the experiment twice each and then change the concentration. I will reduce it by 5 cm3 each time, however each time I will add 5 cm3 of water to dilute the acid, lower the concentration and keep the total volume the same for a fair test.  

Prediction

        There are many things that could, would and should affect the rate of a reaction. All of them effect the rate in a certain way. A catalyst effects the rate of a reaction but is not used up during it. They do this by lowering the ‘activation energy’ (the energy required for two particles to react) of one or both of the reactants. Changing the temperature of 1 of the reactants affects the rate of the reaction by increasing the vibration rate of the particles therefore increasing the chance of the particles ’bumping’ into each other which in turn increases the speed t which the reaction takes place. In creasing the surface area of a particle increases the chance of the acid particles hitting the object (e.g. marble chips) as there is more area TO hit. Increasing the concentration increases the amount of particles in a solution (i.e. there are fewer particles in a 1-molar/litre acid than a 2 molar/litre) this increases the chance of a reaction as there are more particles to react with.

        I predict that as the concentration of the acid lowers, so will the rate of the reaction. This is because as there are less particles to react with as the concentration decreases (the acid becomes more diluted) so there will be less chance of the particles ’bumping’ into each other. I base these predictions on the Collision Theory.

Equipment

        I will use the following items:

2x boiling tube

1x beaker

1x measuring tube

Hydrochloric acid

Sodium Thiosulphate

Water