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The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2018 - Paper 1
Question 6
The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated. The apparatus used is shown in Figure 6. The volume ... 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 Combined Science - Question 6 - 2018 - Paper 1
Step 1
Step 2
Calculate the rate of reaction at this point.
Answer
To find the rate of reaction, we must calculate the gradient of the tangent drawn to the curve at the specified point. Using two points on the tangent, the formula ext{Rate of Reaction} = rac{ ext{change in volume}}{ ext{change in time}} can be utilized. If, for example, the tangent is assessed at the coordinates (15 cm³, 43 s) and (60 cm³, 60 s), we can calculate the rate as follows: ext{Rate} = rac{60 - 15}{60 - 43} = rac{45}{17} ext{ cm}^3/ ext{s} ext{ (approximately 2.65 cm}^3/ ext{s}).
Step 3
On the graph in Figure 7, draw the line you would expect to obtain if the magnesium ribbon in this experiment was replaced with an equal mass of powdered magnesium.
Answer
The line representing the reaction with powdered magnesium would be steeper than the original line with magnesium ribbon, indicating a faster rate of reaction. The new line would start from the same initial point and rise more sharply, likely leading to a greater volume of hydrogen gas being produced in a shorter time while eventually leveling off at a similar 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, we use the formula: ext{Number of moles} = rac{ ext{Mass (g)}}{ ext{Molar mass (g/mol)}}. Given the mass of the magnesium ribbon is 0.1 g and the molar mass of magnesium (Mg) is 24 g/mol: ext{Number of moles} = rac{0.1 ext{ g}}{24 ext{ g/mol}} = 0.00417 ext{ mol}.
Step 5
Use the equation to show that, in this experiment, the magnesium is in excess.
Answer
The balanced chemical equation shows:
ightarrow ext{MgCl}_2 + ext{H}_2 $$. In the experiment, 0.5 mol of HCl reacts with 0.5 mol of Mg. However, for each mole of Mg, 2 moles of HCl are required for complete reaction. Therefore, 0.5 mol of Mg would theoretically need: $$ 0.5 ext{ mol Mg} imes 2 ext{ mol HCl/mol Mg} = 1 ext{ mol HCl} $$. Since there is only 0.5 mol of HCl available, magnesium (Mg) is in excess in this reaction.