How does the change in hydrochloric acid concentration affect the rate of reaction between sodium thiosulfate (Na2S2O3(aq)) and hydrochloric acid (HCL(aq))?
Background to the Research question
Collision Theory
Back in 1916, scientists William Lewis and Max Trautz proposed the collision theory, which qualitatively explains how chemical reactions take place and why reaction rates change for various reactions.
Chemical reactions involve collisions amongst reactant particles or atoms to form bonds. The collision frequency describes the number of times a particle collides with others per unit of time. Nevertheless, not all collisions will be successful. In order for particles to result in a reaction, a Swedish scientist named …show more content…
The reaction between sodium thiosulphate and hydrochloric acid forms the word / chemical equation below:
sodium thiosulphate + hydrochloric acid -> sulfur dioxide + sulfur + water + sodium chloride
Na2S2O3 (aq) + 2HCl (aq) -> SO2(aq) + S(s) + H2O(l) + 2NaCl (aq)
When sodium thiosulphate reacts with diluted hydrochloric acid, a mixture of sulphur dioxide, sulphur and water will be formed. Both sodium thiosulphate and hydrochloric acid are clear and colourless solutions. Sulphur dioxide is a very soluble gas and will dissolve completely within the aqueous solution. The sulphur formed, however, is not soluble and will remain in the mixture as a pale yellow precipitate. This causes the reaction mixture to become opaque and cloudy as the reaction occurs. If the reaction is carried out inside a beaker that is standing on top of a piece of paper marked with a “X” mark, the precipitate will eventually be thick enough to cover the whole “X” mark and make it invisible. Therefore, how concentration affects the rate of reaction between sodium thiosulphate and hydrochloric acid can be easily studied as we measure the time for the “X” mark to fade away and …show more content…
Average time taken for the “X” mark to be covered by the opaque