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To find out how changes in concentration of a solution affect the rate of the reaction.

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RATES OF CHEMICAL REACTIONS AIM: To find out how changes in concentration of a solution affect the rate of the reaction. INTRODUCTION: Chemical reactions occur all a round us. Some reactions are slow, like iron rusting and some are fast like potassium reacting with water or paper burning. There are several factors that affect the speed of a reaction: concentration of solutions, surface area of solids, temperature of reactants, the presence of a catalyst, the pressure of gasses Before I consider each of the above factors we need to look at the nature of matter. We all know that water can exist as ice (solid), water (liquid), or water vapour (gas). These are three states of matter, solid, liquid and gas. KINETIC THEORY This explains how all matter is made up of tiny particles and how these particles are arranged. In a solid the each particle is strongly attracted to all other particles so the particles are held very close together. This explains why solids have a high density. These particles form a regular arrangement so solids have a definite shape and size. Each particle vibrates about a fixed position. When the solid is heated the particles vibrate more and take up more space. ...read more.


Imagine dodgem being driven by blindfolded people at a very slow speed. You would have to wait a long time for there was a crash and the crash would be very gentle. Now imagine these same dodgem cars being driven very fast. You wouldn't have to wait very long for a crash and since they were going fast the crash would be violent. CATALYST A catalyst is a substance that speeds up the rate of a chemical reaction. The Lock & Key Theory offers an explanation as to how it works. Thee catalyst provides a surface on which the reactants 'meet' and then combine. The substrate provides a site for the reactants to meet. The reactant molecules have exactly the right shape to fit into the site like a lock and key. While held in this position the particles react. RATE OF REACTION OF SODIUM THIOSULPHATE WITH HYDROCHLORIC ACID When sodium thiosulphate reacts with hydrochloric acid a yellow precipitate is formed. The reactants are colourless but as the reaction takes place the liquid turns yellow and it is no longer possible to see through the liquid. ...read more.


Your line should look like the one above - but draw your line full length. CONCLUSION I predicted that the more concentrated the sodium thiosulphate the faster would be the reaction. This prediction was correct. For the concentrations of sodium thiosulphate used my results show that the rate of reaction is directly proportional to the concentration. EVALUATION I think my method worked well although it was not easy to decide the exact time at which the X disappeared. If I were to do the experiment again I would use a light meter. I would set up the meter to measure the amount of light passing through the solution. When the meter reached a particular point I would stop the stopwatch. If I were to do the experiment again I would use more varied concentrations and in particular would use 15 ml, as there is a big difference between the rate of reaction with 10 ml and the rate of reaction with 20 ml of sodium thiosulphate. I drew the graph when I had finished the experiment. Next time I do an experiment I will try and do the graph at the same time. This will help me decide if I need to more readings and, if so, where the readings should be. ?? ?? ?? ?? Page 8 ...read more.

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