Investigate the effect of reducing the concentration of Sodium Thiosulphate on the speed of the reaction.

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Alexandra Salters 11HLSC1 Mrs. Seggie Oct/Nov 2002

Chemistry Coursework

Introduction:  When Hydrochloric acid and sodium Thiosulphate are mixed a chemical reaction occurs which produces a precipitate sulphur. This is cloudy in appearance and eventually enough is produced to obscure a cross on a piece of paper. You can get a measure of how fast the reaction works by timing how long it takes to obscure the cross.

Aim of Experiment: I am going to investigate the effect of reducing the concentration of Sodium Thiosulphate on the speed of the reaction.

Prediction: I think that as the concentration decreases the reaction will become slower. I think this will because from my scientific knowledge I know that when we decrease the concentration of Sodium Thiosulphate there are fewer particles of Sodium Thiosulphate. Therefore there are fewer chances for the particles to successfully collide with the acid in order for them to react. I also think if I have half the concentration of the Sodium Thiosulphate the time will double. I think this because as I half my concentration the particles will take double the time to react, this will therefore mean half the chance of successful collisions between particles. The 1st diagram shows the particles at the beginning of the experiment. The black dots represent the Sodium Thiosulphate there are more particles of this. The pink dots represent the water there are very few of these. The water which will dilute the Sodium Thiosulphate as the experiment continues, and the White dots are the Hydrochloric acid these stays the same throughout the experiment. The 2nd Diagram shows the particles at the end of the experiment. The pink dots represent the water, which has now diluted the solution. The white dots are the same because the acid is a constant. There are fewer black dots because we have decreased the concentration.

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Diagram 1                                  Diagram 2

Scientific Knowledge

Collision theory

This is when more particles are added to give a greater concentration. This is done because with there being more particles within the mixture there will be more successful collisions. We can also have more successful collisions by heating the mixture, stirring it and also increasing the concentration.

Kinetic Theory

When the Particles within the experiment are heated it will cause them to move much more quickly therefore there will ...

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