This question is about the reaction between sodium thiosulfate and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 3 - 2022 - Paper 2
Question 3
This question is about the reaction between sodium thiosulfate and hydrochloric acid.
The equation for the reaction is:
Na2S2O3 (aq) + 2 HCl (aq) → 2 NaCl (aq) + SO... show full transcript
Worked Solution & Example Answer:This question is about the reaction between sodium thiosulfate and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 3 - 2022 - Paper 2
Step 1
What is the reason for the mass difference?
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Answer
The mass of the conical flask and its contents is greater at the start because sulfur dioxide gas is produced during the reaction. As the reaction proceeds, this gas escapes into the atmosphere, reducing the total mass in the flask.
Step 2
What type of variable is time in this reaction?
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Answer
Time is a dependent variable as it changes in response to the changes in temperature, which is the independent variable.
Step 3
Complete Figure 4.
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In this step, you would plot the data from Table 1 on the graph, with temperature on the x-axis and time in seconds on the y-axis. Ensure all points are accurately plotted and then draw a line of best fit that represents the trend of the data.
Step 4
Calculate the gradient (slope) of the tangent at 0.4 mol/dm³.
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To calculate the gradient, use the formula:
ext{Gradient} = rac{ ext{change in y}}{ ext{change in x}}
Select two points on the tangent line (for example, (0.3, 20) and (0.5, 10)). Using these points, the gradient calculation would be:
Explain why the rate decreased during the reaction.
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Answer
As the reaction proceeds, there are fewer sodium thiosulfate particles remaining in the solution available to collide with hydrochloric acid particles. This decrease in concentration leads to a decrease in the frequency of successful collisions, thus reducing the reaction rate.
