An investigation into how the concentration of sodium thiosulphate solution affects the rate of its reaction with hydrochloric acid.

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Sam Miranda S5A

An investigation into how the concentration of sodium thiosulphate solution affects the rate of its reaction with hydrochloric acid.

Aim; The aim of this investigation is to see how the concentrations of reactants effect the rate at which a reaction occurs.

The reaction between Sodium Thiosulphate and hydrochloric acid can be used to investigate how the concentration of reactants used can effect the rate at which a reaction occurs. When the two chemicals react, they form a yellow precipitate turning a transparent solution into an opaque one.

By using a beaker with a marked piece of paper positioned underneath it we can react the two chemicals of different concentrations and time the duration of the reaction. The pattern (in this case a cross) will disappear after a specific quantity of Sulphur suspension has formed.

A chemical reaction occurs when two-reactant particles collide with sufficient energy, facing each other in the correct direction. There is always a transfer of energy and a new product formed. There is some times a change in the appearance of the new product.

Adjusting several factors can increase the rate of a reaction. These include; -

Concentration  If we consider a reaction occurring in a solution the greater the concentration is the greater number of reactant particles are present or available. Therefore increasing the concentration will increase the rate of the reaction. The speed of the reaction is directly proportional to the concentration of the solution. This means, if the concentration is doubled them rate of the reaction will double.

Temperature  By altering the temperature of a reaction you can affect or control the rate at which it occurs. If we look at temperature, we know that the motion of the particles will increase because they have gained more energy. This will lead to an increase in the number of collision increasing the rate of the reaction.

At a lower temperature the particles have less energy therefore they move more slowly and have less chance of colliding. At a high temperature the particles move more vigorously and have more chance of colliding and reacting.

Pressure  In gaseous reactions, changing the pressure will alter the rate at which it occurs. Increasing the pressure will increase the density of the number of particles per unit volume leading to more collisions at a faster rate as the particles have less room to move so more chance of coming into contact with each other and reacting. The particles are closer together and have more chance of coming into contact. There is more room in the sealed container so the particles have less chance of coming into contact.

Surface area  When solids are reacted, the surface area that is exposed to the reactant will greatly affect the rate of the reaction. If two equal weights of solid, one in the form of a fine powder and one in the form of one large lump are added to equal amounts of solution the powder will dissolve quicker because more surface area is exposed to the solution. This can be easily understood when looking at sugar. One large lump of sugar will dissolve much slower than caster sugar because more surface area is exposed to the reactant. In addition, the large lump is much harder to break down that the finer caster sugar.

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Catalysts  Theses are chemicals, which are added in a reaction to increase the rate, which it occurs at. Yet they are not actually converted or consumed in the reaction. Specific catalysts are used for each type of reaction. They may often achieve the same product of yield as the normal reactants but with a lower temperature or pressure. Industry finds catalysts very useful and makes good use of them. Lower temperatures and pressure will always be favourable, economical, and safer.

I think the most important factor that affects the rate of the reaction is the concentration because an increase or ...

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