# The Dissapearing Cross

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• Published : January 29, 2011

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Speed of reaction for the cross to disappear when sodium Thiosulpahte is mixed with Hydrochloric Acid…. Introduction
In class we carried out an experiment called `the disappearing cross`. When sodium Thiosulpahte solution is added to acid, the mixture gradually goes cloudy. This can be used to conclude how long the reaction proceeds for. We tried the experiment many times with different amounts of chemicals. In this experiment we will be seeing how the amount of chemical change, will affect the timing of reaction to occur.

The collision theory
Some reactions can be slow such as rusting but some can be fast for example burning. Reactions that occur slowly have a low rate of reaction. Reactions that happen quickly have a high rate of reaction. For a reaction to happen the particles must have enough energy to be able to produce a reaction, if there is not enough energy in the particles the will bash together but no reaction will happen.

What can affect the rate of reaction?
* The effect of temperature
Two molecules will only react if they have enough energy. For two chemicals to react the molecules have to collide with each other and they to have a high rate of energy for the reaction to take place, this is called the collision theory. * Size of surface area

If one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. Smaller particles have a bigger surface area than larger particle for the same mass of solid.

* Catalyst
A catalyst is a chemical that changes the rate of a reaction in a chemical without completely stopping the chemical reaction.

Variables
The concentration of sodium Thiosulpahte is my independent variable, my dependant variable is rate of reaction. I also controlled some variables these were Acid: 5cm3, using the same cross, keeping the temperature the same, we kept these the same to make each experiment we did a fair test with equal or similar results.

Apparatus | Why...