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Practical: Effect of temperature on rate of reaction between acid and thiosulfate ions

The reaction between H⁺_(aq) and thiosulfate ions in solution proceeds in two steps

`text{2H}_text{(aq)}^+ + text{S}_2text{O}_text{3(aq)}^(2-) stackrel text{fast}{->} text{ H}_2text{S}_2text{O}_text{3(aq)} text{ (Thiosulfuric acid)}`

`text{H}_2text{S}_2text{O}_text{3(aq)} stackrel text{slow}{->} text{H}_2text{O}_text{(l)} + text{SO}_text{2(g)} + text{S}_text{(s)}`

Overall: `text{2H}_text{(aq)}^+ + text{S}_2text{O}_text{3(aq)}^{2-} -> text{H}_2text{O}_text{(l)} + text{SO}_text{2(g)} + text{S}_text{(s)}`

This practical will measure the rate at which sulfur is precipitated and see how increasing the temperature affects this rate.

Method

Place 40 cm³ of de-ionised water in a 50 cm³ cylinder and make up to 50 cm³ with 0.15M sodium thiosulfate solution. Place the mixture in a clean dry boiling tube. Place 5 cm³ of 2M hydrochloric acid in a clean dry test-tube. Place both tubes in a water bath. Cool or heat the water bath to the desired temperature and leave the tubes to equilibrate for ten minutes.

Clamp the boiling tube in the path of the laser beam and add the hydrochloric acid. Start the stop-clock and stir the mixture with the thermometer. Take the temperature. Stop the clock when the red dot from the laser can no longer be seen on the white card. Repeat the experiment raising the temperature by 10°C each time.

Apparatus/Chemical List

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Practical

If you wish to see a video of the experiment before carrying out the practical for yourself, click here. The video clip demonstrates the full practical for the effect of temperature on rate of reaction between acid and thiosulfate ions. In the computer version you will undertake the practical from heating the sodium thiosulfate solution to timing the reaction.

Click on the temperature for which you wish to run the practical. If you wish to clear the results of your practical, press Reset

N.B. Reciprocal time (1/t) is a measure of the initial rate of this reaction.

If you wish to use the standard data without answering the questions or carrying out the practical, press Skip one answer, Skip entries or Skip all

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