The Rate of Reaction Between Sodium Thiosulphate and Hydrochloric Acid

The Rate of Reaction Between Sodium Thiosulphate and Hydrochloric Acid

Theory:

Sodium thiosulphate and hydrochloric acid, react together to produce

sulphur as one of the products

Na2S2O3 (aq) + 2HCl (aq)

Sodium Thiosulphate + Hydrochloric acid

à

2NaCl (aq) + H2O (l) + S (s) + SO2 (g)

Sodium Chloride + Water + Sulphur + Sulphur Dioxide

Sulphur is a yellow precipitate, so the solution will turn an opaque

yellow colour while the reaction is occurring. The reaction will

continue and eventually the solutionwill turn completely opaque.

Aim: - the aim of this experiment is to show the effect on the rate of

reaction, when the concentration of one of the reagents changes.

Variables

Dependant Variable: -Variable that is measured. This will be the time,

from when the HCl is added to the Na2S2O3, until the solution goes

yellow and opaque, when a cross, which is written on a label placed

underneath the reaction, can not be see.

Independent Variable: - Variable that is changed. This will be the

concentration of Na2S2O3.

Controlled variable: - There are four variables that may affect the

experiment and the results.

These are concentration and volume of HCl, the same person with the

stopwatch, the same apparatus, temperature these could all affect the

results.

I. Concentration and volume of HCl : - If the concentration is

increased then the number of particles in the solution increases. If

this happens then the number of collisions will increase, and

therefore the number of successful collisions will increase. This is

because the more particles of HCl, then there are more collisions;

therefore the collision frequency is higher. Therefore increasing the

successful collision frequency.

II.The same person with the stopwatch: - The person using the

stopwatch has to stay the same because each person has their own

reaction time, so if another person were to start at the same point,

they could be slower or faster, it would be unlikely that two

different people would have the same reaction time.