To determine what affects the rate at which a reaction occurs between Hydrochloric acid and Sodium thiosulphate.

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Introduction:

The aim of this experiment is to determine what affects the rate at which a reaction occurs between Hydrochloric acid and Sodium thiosulphate. The reaction forms sulphur which is in the form of small solid particles which do not settle: they remain in suspension. I intend to find out whether varying the concentration has any effect on the rate of reaction between these chemicals. I believe that the concentration of Sodium thiosulphate has a direct affect on the rate at which the reaction occurs.

Diagram of apparatus:

Also, goggles will be worn.

Procedure:

* A cross will be marked on a little piece of paper.

* I will dilute the Sodium thiosulphate by way of ratios. I will be measuring 50 cm of solution each time, with a measuring cylinder, but I will vary the volume of Sodium thiosulphate compared to the volume of water (from the tap) diluting it, making different concentrations of Sodium thiosulphate. I will use volumes of 50 cm of Sodium thiosulphate with no water, 40 cm of Sodium thiosulphate with 10 cm of water, 30 cm of Sodium thiosulphate with 20 cm of water and so on down to 10 cm of Sodium thiosulphate with 40 cm of water. I have found from preliminary work that these concentrations react at rates which I can measure quite accurately with the equipment I have.

* First of all, I will pour the 5 cm of hydrochloric acid and 50 cm of Sodium thiosulphate into a conical flask. I will hold the conical flask about 7 cm above the cross and mix the chemicals by swirling the conical flask with my hand, keeping it at the same height. I will observe the reaction with the naked eye looking from above the apparatus. I will start the stopwatch when I start swirling the chemicals and stop it when there's enough sulphur produced to block my view of the cross. The solution should turn yellow.
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* The experiment will be repeated with the different concentrations of Sodium thiosulphate.

* The experiment for each concentration will be repeated two more times, so I will have 15 experiments done altogether. This is to confirm my results just in case there are any anomalies or fluke results.

Variables and why they matter:

* Surface area/ size of particles: Lots of small particles have a larger surface area than the same amount of larger particles. The larger the surface area of the solid, the faster the reaction will be. A higher surface area ...

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