Reaction between thiosulphate and hydrochloric acid

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An Investigation Into The Rate Of The Reaction Between Dilute Hydrochloric Acid And Sodium Thiosulphate

Plan

Aim

The aim of this investigation is to investigate the effect of changes in concentration of the sodium thiosulphate on the rate of the reaction between dilute hydrochloric acid and sodium thiosulphate.

Variables

   There are four main variables that affect experiments such as this. They are:

  • The Temperature Of The Reaction

Reactions get faster as the temperature is increased. As a rough approximation, a 10ºC increase in temperature doubles the rate of a reaction. There are two factors at work here.

  1. Increasing the temperature means that the particles are moving faster and so collide with each other more often. That will make the reaction go faster, but it only accounts for a small part of the increase in rate.
  2. Not all collisions end up in a reaction. Many particles just bounce of each other. In order for anything interesting to happen, the particles have to collide to create a minimum amount of energy called Activation Energy. A relatively small increase in temperature produces a very large increase in the number of collisions which have enough energy for a reaction to occur.

But due to practical limitations the temperature will not be able to be controlled, so will be at the assumed room temperature of 20°C.  

  • The Concentration Of The Products

In general terms, if you increase the concentration of the reactants, the reaction becomes faster. Increasing the concentration increases the chances of particles colliding with each other.

If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules which makes collisions between the important molecules more likely. In a gas increasing the pressure means the molecules are more ‘squashed up’ together so there are going to be more collisions.

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In this case the concentration of the sodium thiosulphate will be the independent variable. That will be changed in order to provoke a reaction from the dependant variable (time taken for the substrate to cover cross completely).  

  • The Catalyst

A Catalyst is a substance which increases the speed of a reaction without being changed or ‘used up’ in the reaction. A Catalyst works by giving the reacting particles a surface to stick to where they can collide with each other. This increases the number of collisions too.

But this investigation will have no catalyst.

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