GCSE AQA Chemistry Combined Science Reactions of Acids: This question is about the react

Question

This question is about the reaction between sodium thiosulfate solution and hydrochloric acid.

The equation for the reaction is:

Na2S2O3(aq) + 2 HCl(aq) → 2 NaCl(aq) + H2O(l) + SO2(g) + S(s)

The mass of the conical flask and contents was greater at the start of the reaction than at the end.

Explain why.

A teacher demonstrated the reaction between sodium thiosulfate solution and hydrochloric acid.

Figure 3 shows the experiment.

The experiment was done in a fume cupboard.

Figure 3

This is the method the teacher used.

1. Pour 50 cm³ of sodium thiosulfate solution into a conical flask.
2. Put the conical flask on a black cross drawn on a piece of paper.
3. Pour 10 cm³ of hydrochloric acid into the conical flask and start a timer.
4. Stop the timer when the cross can no longer be seen.
5. Repeat the experiment at different temperatures.

What type of variable is time in this reaction? Tick (✓) one box.

Control ☐  
Dependent ☑  
Independent ☐

Table 1 shows the results.

Table 1

Temperature in °C  | Time in seconds
--------------------|-----------------
19                  | 82              
32                  | 48              
45                  | 43              
52                  | 15              
63                  | 7

Complete Figure 4.

You should:
- plot the data from Table 1 on Figure 4
- draw a line of best fit.

A student investigated the effect of concentration of sodium thiosulfate on the time taken for the reaction at room temperature.

Figure 5 shows the results with a tangent drawn at 0.4 mol/dm³.

Calculate the gradient (slope) of the tangent at 0.4 mol/dm³

Give the unit.

Gradient =  
Unit =

The student determined the rate of the reaction at regular time intervals during an experiment.

Explain why the rate decreased during the reaction.

You should give your answer in terms of particles.

This question is about the reaction between sodium thiosulfate solution and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 3 - 2022 - Paper 2

Worked Solution & Example Answer:This question is about the reaction between sodium thiosulfate solution and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 3 - 2022 - Paper 2

Explain why the mass of the conical flask and contents was greater at the start of the reaction than at the end.

What type of variable is time in this reaction?

Complete Figure 4.

Calculate the gradient (slope) of the tangent at 0.4 mol/dm³.

Explain why the rate decreased during the reaction.

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