A certain mass of calcium carbonate chunks is added to EXCESS hydrochloric acid solution in an open beaker placed on a scale as shown below - NSC Physical Sciences - Question 5 - 2016 - Paper 2
Question 5
A certain mass of calcium carbonate chunks is added to EXCESS hydrochloric acid solution in an open beaker placed on a scale as shown below. The equation for the rea... show full transcript
Worked Solution & Example Answer:A certain mass of calcium carbonate chunks is added to EXCESS hydrochloric acid solution in an open beaker placed on a scale as shown below - NSC Physical Sciences - Question 5 - 2016 - Paper 2
Step 1
5.1 Is the reaction mixture HETEROGENEOUS or HOMOGENEOUS?
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Answer
The reaction mixture is HETEROGENEOUS. This is because the solid calcium carbonate does not dissolve in the solution and remains as a distinct phase.
Step 2
5.2 Give a reason why the mass of the contents of the beaker decreases as the reaction proceeds.
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The mass of the contents decreases because carbon dioxide gas (CO<sub>2</sub>) escapes into the atmosphere, which reduces the total mass of the system.
Step 3
5.3 How long (in minutes) did the reaction take to reach completion?
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The reaction took 6 minutes to reach completion, as indicated by the stable mass of the beaker and contents after the 6<sup>th</sup> minute.
Step 4
5.4 Calculate the average rate of reaction during the interval 0 to 1 minute in grams per minute.
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To calculate the average rate, use the formula:
extRate=−ΔtΔm
where:
Initial mass at 0 min = 192.4 g
Mass at 1 min = 188.0 g
Thus,
Change in mass, (\Delta m = 188.0 - 192.4 = -4.4 g)
Change in time, (\Delta t = 1 min)
Therefore,
Rate=−1min−4.4g=4.4 g/min
Step 5
5.5 The rate of reaction decreases as the reaction proceeds. Give TWO reasons why the reaction rate decreases.
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As the reaction progresses, the concentration of reactants decreases, leading to fewer effective collisions between particles.
The reaction may generate products (like CaCl<sub>2</sub>) that can create a barrier for further reaction, thus slowing it down.
Step 6
5.6 Apart from CO<sub>2</sub>, write the NAME or FORMULA of another substance that is not present in the container of 6 minutes.
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Another substance that is not present is water (H<sub>2</sub>O) as it's in liquid state, and it exits the reaction mixture.
Step 7
5.7 Calculate the mass of calcium carbonate consumed after completion of the reaction.
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The initial mass of the beaker and contents was 192.4 g, and the final mass was 186.7 g after completion. Therefore, the mass of calcium carbonate consumed is:
192.4g−186.7g=5.7g
Step 8
5.8 Plot a graph of mass of contents of beaker versus time for the time interval from the 0<sup>th</sup> to the 6<sup>th</sup> minute.
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A graph should show a downward trend starting from 192.4 g at 0 minutes, decreasing to 186.7 g at 6 minutes, indicating the mass loss due to the escape of gas.
Step 9
5.9 Use the collision theory to explain how the rate of the above reaction will change when the initial temperature is changed to 50 °C.
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Increasing the temperature to 50 °C will increase the average kinetic energy of the particles. This means that more particles will have sufficient energy to overcome the activation energy barrier, leading to:
More frequent and effective collisions per unit time.
An overall increase in the reaction rate as temperature rises enhances particle movement and interaction.
