Rates of Reaction :: GCSE Chemistry Coursework Investigation

The affect of varying hydrochloric acid concentration of on the rate of reaction with sodium thiosulphate Background knowledge:The equation of this reaction is Na2S2O2+ 2HCl  ± 2NaCl + H2O + SO2+ S A reaction is a process by which a substance or substances change to produce a new substance or substances. Rate of reaction is the speed at which products are formed and reactants disappear during a chemical reaction. The rate will be measured by following the production of sulphur. The rate of reaction is affected by temperature, surface area, concentration and catalysts. These are the affecting factors. In a reaction, the particles of the reagent must come together and collide before the reaction can take place. This is called the collision theory, particles must collide before they can react, and the colliding particles must contain enough energy to cause bonds to brake. Apparatus: * Beaker * 'Log its' light meter * stand * black card * syringe * glass delivery tube * tripod * measuring cylinder * stop watch Method: We decided to use a 'loggits' light meter to follow the precipitation of sulphur on the basis that the light passing through the solution would decrease in intensity as the reaction proceeds. We will firstly cover the beaker with card, leaving a 2cm gap at the bottom of the beaker to allow light to pass through the solution. Secondly we would place the 'loggits' light meter directly above the beaker (the meter will have the bottom half of it covered with the card to prevent any alien light from affecting the light intensity of the light passing through the water) Preliminary: After the first trial we had to change the way in which we covered the beaker with the black card because we found that the amount of light passing through the solution from all angles was uncontrollable, because we were using a natural source of light (the sun). Instead of leaving a 1cm gap from the bottom of the beaker, our solution was to cover the whole beaker and cut 2 arches, so that we could direct the required amount of light into the specific area of the beaker. Secondly we will use a lamp, covered with 2 sheets of A4 paper to achieve a constant source of light. The Initial light intensity reading will be between 40% and 45%. Procedure: Step 1) Set up the stand to hold the log its light meter above the beaker (fig i). Then place the beaker beneath the meter. Form a shielding from the surrounding light by using the black card, doing so by forming a cone around the beaker and the bottom half of the light