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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
State a change that can be made to the apparatus in Figure 6 to measure the volumes of gas more accurately.
Answer
One change that can be made to the apparatus in Figure 6 to measure the volumes of gas more accurately is to use a gas syringe or a graduated tube instead of a measuring cylinder.
Step 2
Calculate the rate of reaction at this point.
Answer
To calculate the rate of reaction at the tangent drawn on the graph, determine the slope of the tangent line. The gradient can be calculated using the formula:
ext{Rate} = rac{ ext{Change in Volume}}{ ext{Change in Time}}
For example, if the tangent intersects the y-axis at 40 cm³ and the x-axis at 60 s, then:
ext{Rate} = rac{40 ext{ cm}^3 - 15 ext{ cm}^3}{60 ext{ s} - 43 ext{ s}} = rac{25 ext{ cm}^3}{17 ext{ s}} \\ ext{Rate} ext{ = } 1.47 ext{ cm}^3 ext{s}^{-1}
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 should be steeper than the original line since powdered magnesium has a greater surface area, which increases the rate of reaction. This line should start at a similar initial volume and rise more steeply, reaching a higher final volume in a shorter amount of time.
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 of magnesium, use the formula:
ext{Number of moles} = rac{ ext{mass (g)}}{ ext{molar mass (g/mol)}}
Substituting the values:
ext{Number of moles} = rac{0.1 ext{ g}}{24 ext{ g/mol}} = 0.00417 ext{ moles}
Step 5
Use the equation to show that, in this experiment, the magnesium is in excess.
Answer
In the equation, we see that 1 mol of Mg reacts with 2 mol of HCl:
In this experiment, we have 0.5 mol of HCl and 0.5 mol of Mg. Since only 0.25 mol of Mg would be required to completely react with 0.5 mol of HCl, the magnesium is in excess.
Step 6
Explain, in terms of the behaviour of particles, the effect of changing temperature and the effect of changing the concentration of A in solution on the rate of reaction.
Answer
Increasing the temperature increases the kinetic energy of the particles, leading to more frequent and energetic collisions, which increases the rate of reaction. On the other hand, increasing the concentration of A results in a greater number of particles in the solution. This leads to more collisions between A and B, hence accelerating the rate of reaction. In summary, both increasing temperature and concentration enhance the likelihood of effective collisions, thus increasing the reaction rate.