This question is about the reaction between sodium thiosulfate solution and hydrochloric acid - AQA - GCSE Chemistry - Question 8 - 2022 - Paper 2
Question 8
This question is about the reaction between sodium thiosulfate solution and hydrochloric acid.
When hydrochloric acid is added to sodium thiosulfate solution, the m... show full transcript
Worked Solution & Example Answer:This question is about the reaction between sodium thiosulfate solution and hydrochloric acid - AQA - GCSE Chemistry - Question 8 - 2022 - Paper 2
Step 1
Why does the mixture become cloudy?
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Answer
The mixture becomes cloudy due to the formation of sulfur as a solid precipitate during the reaction between sodium thiosulfate and hydrochloric acid. The sulfur particles scatter light, reducing the amount of light that passes through the solution.
Step 2
Determine the rate of reaction in moles for the production of sulfur at 30 seconds.
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Answer
To find the rate of reaction at 30 seconds, draw a tangent to the curve at that point on Figure 7. Measure the change in the y-axis (percentage of light reaching the sensor) and in the x-axis (time). Using the formula for the rate of reaction:
Rate=TimeChange in concentration
Calculate the rate based on the tangent coordinates.
Step 3
Explain why the rate of reaction changes between 0 and 60 seconds.
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The rate of reaction decreases between 0 and 60 seconds because the concentration of thiosulfate decreases as it is consumed in the reaction, which results in a lower collision frequency between reactant particles.
Step 4
Why did the reaction stop?
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The reaction stopped because one of the reactants (sodium thiosulfate or hydrochloric acid) was completely consumed, resulting in no further formation of sulfur.
Step 5
Select a few from Figure 8 to show the result you would predict for 0.20 mol/dm³ sodium thiosulfate solution.
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The predicted results would indicate a steeper decrease in light percentage at the start compared to 0.10 mol/dm³ sodium thiosulfate, reflecting a faster rate of reaction due to increased concentration.
Step 6
How could the student improve the method so that the same percentages of light reached the light sensor?
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The student could improve the method by stopping light from other sources reaching the light sensor, thereby ensuring consistent measurements and reducing variability.
Step 7
What was the gain in this similar results obtained on different days under the same conditions to ensure the study was valid?
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The study was valid because the results were repeatable, indicating that the same procedure under the same conditions yields consistent outcomes.
Step 8
Which expression represents the relationship between the volume (V) of sodium thiosulfate solution used and the mass of sulfur produced?
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The expression can be represented as V ∝ m, indicating that the volume of sodium thiosulfate solution is directly proportional to the mass of sulfur produced.
Step 9
Determine the simplest whole number ratio of the volumes of sodium thiosulfate solution - hydrochloric acid.
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The simplest whole number ratio of the volumes is 1:4, indicating that for every part of sodium thiosulfate solution, four parts of hydrochloric acid are used.
