Photo AI
The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated - Edexcel - GCSE Chemistry - Question 9 - 2018 - Paper 1
Question 9
The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated. The apparatus used is shown in Figure 11. The volum... show full transcript
Worked Solution & Example Answer:The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated - Edexcel - GCSE Chemistry - Question 9 - 2018 - Paper 1
Step 1
Step 2
Calculate the rate of reaction at this point.
Answer
The rate of reaction can be calculated using the formula:
ext{Rate of reaction} = rac{ ext{Change in volume}}{ ext{Time taken}}From the graph, if the tangent shows a change in volume from 15 cm³ to 44 cm³ over a time of 60 s,
Change in volume = 44 - 15 = 29 cm³ Time taken = 60 s, Rate = \frac{29 \text{ cm}^3}{60 \text{ s}} = 0.48 ext{ cm}^3/s.
Step 3
On the graph in Figure 12, draw the line you would expect to obtain if the magnesium ribbon in this experiment was replaced with an equal mass of powdered magnesium. All other conditions are kept the same.
Answer
The expected line on the graph should be steeper to the left of the printed curve and should rise faster initially because powdered magnesium reacts more quickly than ribbon. The line would then level off and return to the same final volume.
Step 4
Calculate the number of moles of magnesium, Mg, in the 0.1 g sample of magnesium ribbon.
Answer
To calculate the number of moles, use the formula:
ext{Number of moles} = rac{ ext{Mass in g}}{ ext{Molar mass in g/mol}}Given that the relative atomic mass of magnesium, Mg, is 24:
Number of moles = \frac{0.1}{24} = 0.00417 ext{ moles (approximately)}.
Step 5
Use the equation to show that, in this experiment, the magnesium is in excess.
Answer
The balanced equation is:
In the experiment, 0.5 mol of HCl reacts with 0.25 mol of Mg as it requires 2 moles of HCl for every mole of Mg. Since 0.5 mol HCl can react with only 0.25 mol Mg, magnesium is in excess in this reaction.