Decomposition Of Sodium Thiosulphate Essay

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Register to read the introduction… • The temperature in the room may have altered.

A dependent variable is a variable you do not change during an experiment. Instead, it changes as a result of other changes you make.

The dependent variables in my experiment were:
• The rate of reaction.
• The volume of sodium thiosulphate.

The volume of sodium thiosulphate will remain unaffected throughout the whole experiment, Where as I will be changing the concentrations of hydrochloric acid. The volume of sodium thiosulphate will be 50cm³. The different concentrations of hydrochloric acid are 0.10M, 0.25M, 0.50M, 0.60M, 0.90M and 1.0M.

Now, I will discuss my prediction of what will happen during the experiment.


My prediction is,
• As I increase the concentration of hydrochloric acid and add it to the sodium thiosulphate the rate of reaction will decrease.

This happens because more particles are being added to the solution when the concentration increases. Therefore, this decreases the rate of reaction and the probability of a collision between reactant particles because there are more of them in the same volume and so increases the chance of a collision forming. This is where the collision theory starts in gases, increase in pressure means those molecules are closer together so there are more
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Effect of Surface area:

If there is a greater surface area of a reactant there is a bigger chance of a collision occurring between the particles. If one of the reactants is a solid then breaking it up into smaller pieces will increase the surface area. This means the particles around it in the solution will have more to work to do so there will be more useful collisions.

Effect of Concentration:

Increasing the concentration means you are adding more particles to a solution which also increases the reaction time.
If the concentration of any reactant in a solution is increased, the rate of reaction is increased.

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

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