Investigate the affect of changing the concentration of Sodium Thiosulphate, on the reaction between Hydrochloric Acid and Sodium Thiosulphate.

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Jennifer Gowdy 12C 2001                 Chemistry Coursework – Rate of Reaction

Rate of reaction

Investigate the affect of changing the concentration of Sodium Thiosulphate, on the reaction between Hydrochloric Acid and Sodium Thiosulphate.

Variables

  1. The concentration of Sodium Thiosulphate
  2. The concentration of Hydrochloric Acid
  3. Temperature of both solutions
  4. Volume of Sodium Thiosulphate
  5. Volume of Hydrochloric Acid
  6. The depth of each solution in the conical flask
  7. The intensity and duration of mixing of the solution

The investigation will determine how the concentration of Sodium Thiosulphate will affect the reaction between Hydrochloric Acid and Sodium Thiosulphate.

What to change

The concentration of Sodium Thiosulphate will be changed during the investigation.

What to measure

The time taken for a certain amount of precipitate to be produced to obscure a pencilled ‘x’ will be measured. (The pencilled ‘X’ will be on a white piece of paper on which the conical flask will stand.)

What to keep the same

  1. The concentration of Hydrochloric Acid
  2. Temperature of both solutions
  3. Volume of Sodium Thiosulphate
  4. Volume of Hydrochloric Acid
  5. The depth of each solution in the conical flask
  6. The intensity and duration of mixing of the solution

Prediction

It is predicted that as the Sodium Thiosulphate is concentrated, the precipitate will be formed faster.  

If the concentration of a solution is increased there are more reactant particles per unit volume, this increases the probability of reactant particles colliding with each other.  To react, particles have to overcome an ‘energy barrier’.  Only particles with enough energy to overcome the barrier will react after collision.

The increase in concentration of Sodium Thiosulphate will increase the availability of reactant particles – Sodium Thiosulphate ions.

This increased availability will speed up the reaction allowing faster formation of the precipitate.

The pencilled ‘X’ on the paper will therefore be obscured more quickly as the yellow coloured precipitate forms and reduces the visibility down through the solution. (The precipitate formed is Sulphur which remains in suspension.)

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If the concentration of Sodium Thiosulphate is diluted, less Sodium Thiosulphate ions are present, causing fewer reactant particles to be present and therefore reducing the number of collisions with Hydrochloric Acid ions.  In addition, there will be an increase in the number water ions.  Water ions will have no effect on the formation of the precipitate.  The result will be a slower time of reaction for precipitate formation allowing the pencilled ‘X’ to stay visible for a longer period of time.

The charges on the ions are given below:

Na2 1+  S2O3 2-   H1+   Cl 1-

Therefore, the ...

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