Effects of Concentration of Sodium Thiosulphate in the reaction of Hydrochloric Acid and Sodium Thiosulphate.

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Chemistry Coursework                5089

Balanced Equations

Sodium Thiosulphate + Hydrochloric Acid                   Sodium Chloride + Water + Sulphur Dioxide +    Sulphur

Na2S203 (aq) + 2 HCl (aq)                                                  2NaCl (aq) + H2O (l) + SO2 (g) + S (s)

Ionic Equation

S2O32-  (aq) + 2H + (aq)                                                   H20 (l) + SO2 (g) + S (s)

Rate of reaction is how fast or slow a chemical reaction takes place and there are a number of different factors which will affect the rate of a reaction and these are:

  • Temperature
  • Surface Area
  • Concentration
  • Catalysts
  • Light

The higher the temperature, the faster the rate of reaction will occur; as the particles have more energy and therefore will collide more.  By increasing the surface area we increase the rate of reaction as there is a larger area over which the particle can collide and react together. The same general idea can be said for concentration, the higher it is, the quicker the rate is as there are more particles to collide and react together. A catalyst is a substance added to a reaction to speed it up without going under any permanent chemical change itself. For the reaction we are discussing, there is no catalyst present so it has no effect on it. Light can also affect the time a reaction takes by speeding it up. These reactions are called photochemical reactions and it not relevant to the experiment I will be conducting.

The general formula used to find the rate of a reaction is:

Rate = Change in Measured Quantity ÷ Time taken

When these two react, sulphur is formed as a white precipitate which clouds the solution. A possible way of measuring the reaction would be to draw an ‘X’ on a white tile beneath the conical flask, and using a stopwatch, measure how long it takes before the ‘X’ disappears from view. A precipitate is an insoluble substance formed when two solutions are mixed, in this reaction it is Sulphur. The sulphur is what will obscure the ‘X’ so therefore it can be said that I would be finding the rate at which a certain amount of sulphur is produced in the reaction.

Variables

   For an experiment of this nature it would be possible to change the volumes of the solutions used, the temperature at which the experiment is conducted or the concentration of one of the solutions involved. No catalysts are involved and light will have no effect of the reaction.

   My independent variable, what I shall change, will be the concentration of the sodium thiosulphate used in the reaction.

   My dependent variable, what I shall measure, will be the time taken for the ‘X’ to disappear from view due to the reaction that is taking place.

  My controlled variable, what I will keep the same, will be the volume and concentration of hydrochloric acid. The temperature at which the reactions take place will be constant also. These are to remain the same so as to keep the test fair.

Prediction

   I predict that as the concentration of sodium thiosulphate decreases, the time taken for the ‘X’ to disappear will increase proportionally. Thus they will be inversely proportional to each other as demonstrated in my sketch graph below.

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Procedure

Diagram of Apparatus

Method

  1. Set up apparatus as shown above with the conical flask on top of the tile with the ‘X’ on it.
  2. Using the 10ml measuring cylinder, measure out 10ml of HCl.
  3. Using the 50ml measuring cylinder, measure out 50ml of Sodium Thiosulphate.
  4. Add the 50ml of Na2S203 to the conical flask, followed by the 10ml of HCl. ...

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