An investigation into the factors affecting the rate of a reaction: The write up of an experiment using Sodium Thiosulphate and hydrochloric acid

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Skill Area P: Planning

What I going to investigate is how different factors affect the rate of the chemical reaction of Sodium Thiosulphate and Hydrochloric acid. In which a precipitate is formed and causes the solution to become opaque. They react as in the equation below:

Sodium Thiosulphate + hydrochloric acid -->; sodium chloride + sulphur + sulphur



Na2S2O3(aq) + 2HCl(aq) -> 2NaCl(aq) + S(s) + SO2(g) + H2O(l)

I plan to change the concentration of the Sodium Thiosulphate by diluting it with water but I plan to keep the same volume of liquid in the beaker to ensure that it is a fair test because the volume of liquid in the beaker may affect the reaction time. Also in order to make it a fair test I am going to keep the following variables the same: the temperature; the volume of the hydrochloric acid; the same distance between the light sensor and the solution; the same distance from the light source and the solution; the voltage going into the light bulb; same concentration of acid; same beaker and apparatus; and the same total volume.

I have identified the following hazards and I will deal with them as shown below:

Hazard 1: Dealing with Acids -- I will wear safety specs to protect my eyes and care will be taken while handling the acid.

Hazard 2: Electrical Equipment - I will not touch the electrical equipment while handling liquids and care will be taken to make sure that all electrical equipment will not come into contact with liquids.



A beaker



Light Source (I used a 6V bulb)(Surround the light with a ring of black cardboard to focus the light

Light sensor (again surround the sensor with black cardboard to irradiate light from other sources)



Clamp stand

Sodium Thiosulphate

Hydrochloric Acid

Firstly I set the computer up and loaded the software, which I used to record the data. I then attached the light sensor onto the clamp...
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