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The Reaction between Sodium Thiosulphate and Hydrochloric Acid.

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The Reaction between Sodium Thiosulphate and Hydrochloric Acid Introduction The "rate of reaction" is defined as the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. This piece of coursework is an investigation into "rates of reaction" between sodium thiosulphate and hydrochloric acid and the effect that different concentrations have on them. It may be noted that when sodium thiosulphate and hydrochloric acid are mixed together the mixture precipitates. It turns cloudy and then a creamy white colour which turns yellow and becomes thicker until it eventually solidifies. There are five factors which affect the rate of a reaction, according to the collision theory of reacting particles: Temperature; The rate of reaction will increase if the temperature is raised. Heat gives more particles an energy greater than the activation energy causing them to collide more often and with greater force. It will be hard to control this factor but I will try to keep it as close to room temperature as possible. Concentration (of solution); The rate of reaction will increase if the concentration of one or more of the reactants is increased because there will be more molecules in the same space so more collisions will occur. ...read more.


I will record repeat results and averages to improve the credibility of my findings. The repeat results will help remove any anomalies and the average will give a good summary of the results. 5 In all cases the experiments will be conducted at room temperature. Safety I will wear a pair of safety goggles to protect my eyes Controlled Variables * Same amount of hydrochloric acid * Same total volume of solution * Same cross * Same size beaker * Same stopwatch * Same person using the stopwatch * Same person judging how long it takes for the cross to disappear * Ambient temperature is the same The controlled variables are to make the experiment a fair test. Key Factors Temperature - Must be kept the same as an increase in the temperature will cause the reaction time to increase. This is because the heat energy gives the particles greater activation energy. Concentration - This is the variable I am going to change. I expect that as the concentration increases the reaction time will decrease. This is because there will be more molecules in the same space, blocking the light. Preliminary experiments I estimated which concentrations to use during my preliminary set of experiments and I tried the first and last values. ...read more.


There are several things I would change if I were to do this investigation again. 1 I would monitor room temperature and attempt to perform all three experimental "Tries" in quick succession (or even in parallel). 2 It's not particularly accurate to judge when the cross has disappeared by eye as a person's view of when they can't see it can change which will affect the results. Ideally I could use a lamp and light sensor. I could also use a colorimeter which is a device used to compare or measure colours and their intensities. This would be able to show when the solution had finally precipitated by 'showing' when there was no longer any light being let through the solution. 3 As well as more accurate ways of telling when the mixture had fully precipitated there are also more accurate ways of measuring out the liquid such as using burettes/pipettes which measure accurate to 0.1ml instead of the measuring cylinder I used which only measures to 1ml. Nevertheless I think the evidence I have collected is sufficient to support a conclusion that as the concentration increases the rate of reaction increases. To extend the enquiry I could do further experiments where I would keep the concentrations the same but change the temperature. ...read more.

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