This question is about the reaction between sodium thiosulphate solution and hydrochloric acid - AQA - GCSE Chemistry - Question 8 - 2022 - Paper 2
Question 8
This question is about the reaction between sodium thiosulphate solution and hydrochloric acid.
When hydrochloric acid is added to sodium thiosulphate solution, the... show full transcript
Worked Solution & Example Answer:This question is about the reaction between sodium thiosulphate 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 solid sulfur as a product of the reaction between sodium thiosulphate and hydrochloric acid. The solid sulfur formed suspends in the solution, scattering light and making the solution appear cloudy.
Step 2
Determine the rate of reaction in moles for the production of sulfur at 30 seconds.
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Answer
To determine the rate of reaction, we need to draw a tangent to the curve at 30 seconds on Figure 7. We can find the coordinates of the tangent line at this point and calculate the rate of reaction using the formula:
Rate=ΔxΔy
where (\Delta y) is the change in the percentage of light detected and (\Delta x) is the change in time.
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 the reactants decreases as they are used up in the reaction. Initially, the concentrations are highest, leading to a higher collision frequency and rate, but as time progresses and reactants are consumed, the collision frequency decreases, resulting in a lower rate.
Step 4
Why did the reaction stop?
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The reaction stopped because one of the reactants was completely consumed. In this case, all the sodium thiosulphate or hydrochloric acid would have been used up in the reaction.
Step 5
Select a line from Figure 8 to show the result you would predict for 0.20 mol/dm³ sodium thiosulphate solution.
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The predicted line for 0.20 mol/dm³ sodium thiosulphate solution would show a steeper initial decrease in light percentage compared to the 0.10 mol/dm³ solution, reflecting a faster reaction rate due to the higher concentration.
Step 6
How could the student improve the method to ensure that the same percentages of light reached the light sensor?
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The student could improve the method by ensuring that there are no other sources of light reaching the light sensor, which would help in obtaining consistent readings.
Step 7
What was similar in this experiment compared to experiments conducted on different days under the same conditions?
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The results obtained from this experiment were repeatable, as the same method should yield similar results if the conditions are kept the same.
Step 8
Which expression represents the relationship between the volume (V) of sodium thiosulphate solution used and the mass (m) of sulfur produced?
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The expression would be based on stoichiometry and can be represented as:
volume of HClvolume of Na2S2O3=Vmass of sulfur produced
where V is the variable volume of sodium thiosulphate.
Step 9
Determine the simplest whole number ratio of the volumes of sodium thiosulfate solution: hydrochloric acid.
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After performing the necessary calculations based on the volumes provided and their respective concentrations, the simplest whole number ratio of sodium thiosulfate solution to hydrochloric acid is found to be 1:4.
