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Sodium thiosulfate solution, Na2S2O3, reacts with dilute hydrochloric acid - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2020 - Paper 1
Question 3
Sodium thiosulfate solution, Na2S2O3, reacts with dilute hydrochloric acid. Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + SO2(g) + S(s) (i) When dilute hydrochlori... show full transcript
Worked Solution & Example Answer:Sodium thiosulfate solution, Na2S2O3, reacts with dilute hydrochloric acid - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2020 - Paper 1
Step 1
Explain why the mixture turns cloudy.
Answer
When dilute hydrochloric acid is mixed with sodium thiosulfate, a chemical reaction occurs that produces sulfur as a solid. This solid sulfur forms small particles suspended in the solution, scattering light and causing the mixture to appear cloudy. The cloudiness is due to the formation of these sulfur particles, which disrupt the clarity of the liquid.
Step 2
Describe how the rate at which the mixture goes cloudy can be measured.
Answer
The rate at which the mixture goes cloudy can be quantitatively measured by timing how long it takes for a marked cross or black dot, placed underneath the reaction vessel, to disappear from view as the cloudiness increases. The shorter the time taken for the cross to disappear, the faster the reaction is occurring. Alternatively, variations in the light transmission through the mixture can be measured using a colorimeter.