Hydrochloric Acid and Sodium Thiosulphate: How Reaction Rate Varies with Sodium Thiosulphate Concentration

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Title Hydrochloric acid and sodium thiosulphate: how reaction rate varies with sodium thiosulphate Concentration Introduction When sodium thiosulphate reacts with hydrochloric acid, sulphur is produced. The sulphur that is produced forms in very small particles and causes the solution to cloud over and turn a yellow colour. This basic word equation sums up the reaction: HCL + sodium thiosulphate sodium chloride + sulphur dioxide + sulphur + water The aim of this experiment is to observe and record the rate of reaction of hydrochloric acid and sodium thiosulphate; a conical flask above a marked 'x' will be filled with the required amounts of hydrochloric acid and sodium thiosulphate and then the amount of time it takes for the reaction to occur and for the marked 'x' to disappear will be measured. The scientific principle in effect here is the collision theory. The collision theory is the theory that molecules have to collide in a certain way with a certain amount of energy in order to react and form a new product; when molecules collide that can react, they need a certain amount of energy (also known as activation energy) in order to break existing bonds and then form new bonds as the new product. Many factors can affect the collisions of the molecules which will in-turn affect the rate of reaction such as temperature, concentration, use of a catalyst and surface area (1, 2). The effects concentration has on the collisions of the molecules will be looked at since this comes into correlation with the experiment at hand; the more concentrated a solution is, means the more molecules there are to collide which will mean a higher rate of reaction if the concentration is being raised and a slower rate of reaction if the concentration is being lowered. Since in this experiment the concentration of sodium thiosulphate will be lowered each time, the effective

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