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A student investigates the reaction between magnesium and dilute hydrochloric acid, HCl - OCR Gateway - GCSE Chemistry - Question 19 - 2019 - Paper 4
Question 19
A student investigates the reaction between magnesium and dilute hydrochloric acid, HCl. The student adds magnesium ribbon to hydrochloric acid in a beaker, as show... show full transcript
Worked Solution & Example Answer:A student investigates the reaction between magnesium and dilute hydrochloric acid, HCl - OCR Gateway - GCSE Chemistry - Question 19 - 2019 - Paper 4
Step 1
Step 2
Describe and explain whether the student’s results support his prediction.
Answer
The student's prediction states that "the smaller the volume of acid and the greater the concentration of acid, the faster the reaction rate."
Upon analyzing the results:
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Reaction times for experiments 1 and 2: Both used 0.05 g of magnesium but differ in volume of acid (25 cm³ and 50 cm³) with the same concentration. The reaction times are 30 seconds for both, indicating that volume does not impact reaction time when concentration remains unchanged.
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Comparison of experiments 3 and 5: In these experiments, the amount of magnesium (0.10 g) is constant, but the concentration varies (1.0 mol/dm³ and 2.0 mol/dm³). The reaction time decreased from 30 seconds (1.0 mol/dm³) to 15 seconds (2.0 mol/dm³), supporting the idea that higher concentration accelerates the reaction.
This supports the prediction about concentration but shows that the volume of acid does not influence the rate if concentration remains constant.
Step 3
Explain, using the reacting particle model, what happens to the rate of reaction and predict the reaction time for this reaction.
Answer
Increasing the temperature leads to greater energy in the reacting particles, causing them to move more rapidly. This results in more frequent and energetic collisions between magnesium and hydrochloric acid molecules, thus increasing the rate of reaction.
As a prediction, the reaction time will decrease compared to that at room temperature. If the initial reaction time is 30 seconds, it can be expected to be approximately 20 seconds or less at a higher temperature, depending on the exact temperature change.
Step 4
Calculate the mean rate of reaction in experiment 2.
Answer
To calculate the mean rate of reaction, we use the formula:
For experiment 2:
- Mass of marble chips: Not specified in the table, but let’s assume it’s the same as in experiment 1, which is equivalent to 0.05 g.
- Reaction time: 120 seconds.
Thus, the calculation will yield:
Expressed in standard form to 3 significant figures, the answer is: