Chemistry SC1 Investigation: How does the temperature affect the rate of reaction between sodium thiosulphate and hydrochloric acid?

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Chemistry SC1 Investigation: How does the temperature affect the rate of reaction between sodium thiosulphate and hydrochloric acid?

Skill P - Planning:

Background:

Sodium Thiosulphate is white solid with the chemical formula Na2S2O3. It can be made by reacting sulphur dioxide with sulphur in boiling sodium hydroxide solution.

S + SO2 + 2NaOH › Na2S2O3 + H2O

Hydrochloric acid is a colourless, corrosive, non-flammable liquid. Its formula is HCl.

Factors that could affect the rate of reaction between sodium thiosulphate and hydrochloric acid:

* The concentration of the hydrochloric acid. If the acid has a high concentration e.g. 5moles/litre, it will react quicker than a less concentrated, more dilute acid.

* The concentration of the sodium thiosulphate will also affect the rate of reaction in the same way.

* The temperature of the sodium thiosulphate, thus the temperature the reaction will take place at, will affect the rate of the reaction. At lower temperatures, the reaction will take a long time, as little heat energy is available for the hydrochloric acid and sodium thiosulphate molecules to convert into kinetic energy. However, at higher temperatures, lots of heat energy will be converted into kinetic energy. The molecules will be moving around at higher speeds. This increases the chance of a successful collision, and hydrochloric acid and sodium thiosulphate molecules will easily have enough activation energy to join together. Temperature will be used as the factor in the final experiment.
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* Whether a catalyst is present or not will, also, affect the rate of reaction. A catalyst speeds up the rate of a reaction and can be retrieves at the end chemically unchanged.

Trial experiments carried out:

A trial experiment was carried out to determine what concentration of sodium thiosulphate is to be used. Several concentrations were tested at room temperature, then at 50°C, (the thiosulphate concentration is 40g/litre):

* 20% sodium thiosulphate to 80% water

* 40% sodium thiosulphate to 60% water

* 60% sodium thiosulphate to 40% water

* 80% ...

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