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Fireworks contain a range of chemicals including a fuel, oxidising agents and metal salts - Scottish Highers Chemistry - Question 2 - 2022
Question 2
Fireworks contain a range of chemicals including a fuel, oxidising agents and metal salts. (a) One oxidising agent used in fireworks is potassium perchlorate, KClO₄... show full transcript
Worked Solution & Example Answer:Fireworks contain a range of chemicals including a fuel, oxidising agents and metal salts - Scottish Highers Chemistry - Question 2 - 2022
Step 1
Balance this equation.
Answer
To balance the equation KClO₄ + Al → KCl + Al₂O₃, we can follow these steps:
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Count the number of each type of atom in the unbalanced equation:
- K: 1 (left) vs 1 (right)
- Cl: 1 vs 1
- O: 4 (in KClO₄) vs 3 (2 in Al₂O₃ and 1 in KCl)
- Al: 1 vs 2
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Adjust coefficients to balance the aluminum and oxygen:
- Place a coefficient of 3 in front of KClO₄ and 2 in front of Al:
3KClO₄ + 2Al → 3KCl + Al₂O₃
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Confirm that each side of the equation has equal numbers of each type of atom:
- K: 3 (left) vs 3 (right)
- Cl: 3 vs 3
- O: 12 (left, from 4 in 3KClO₄) vs 12 (right, from 3KCl and 3 in Al₂O₃)
- Al: 2 (left) vs 2 (right)
Thus, the balanced equation is:
3KClO₄ + 2Al → 3KCl + Al₂O₃.
Step 2
Calculate the volume of oxygen produced, in litres, when 4.6 g of potassium chlorate decomposes.
Answer
-
Calculate moles of KClO₃:
(GFM = 122.6 g):
[ ext{Moles} = \frac{4.6 \text{ g}}{122.6 \text{ g/mol}} \approx 0.03752 ext{ moles} ] -
From the balanced reaction, we can see that 2 moles of KClO₃ produce 3 moles of O₂:
[ 2KClO₃(s) \rightarrow 3O₂(g) ]
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Calculate moles of O₂ produced:
[ \text{Moles of } O₂ = 0.03752 \text{ moles of KClO₃} \times \frac{3 ext{ moles O₂}}{2 ext{ moles KClO₃}} \approx 0.05628 ext{ moles O₂} ]
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Using the molar volume (24 L/mol) to find the volume of O₂ produced:
[ \text{Volume of } O₂ = 0.05628 \text{ moles} \times 24 \text{ L/mol} \approx 1.35 \text{ L} ]
Therefore, the volume of oxygen produced is approximately 1.35 litres.
Step 3
State the effect of adding a catalyst on the enthalpy change for this reaction.
Answer
Adding a catalyst to a chemical reaction does not change the enthalpy change of the reaction. The catalyst simply provides an alternative pathway with a lower activation energy for the reaction without altering the overall energy difference between reactants and products.
Step 4
Calculate the energy, in kJ, released per mole of potassium perchlorate.
Answer
To find the energy released per mole, we need to find how many moles are in 5.5 g of potassium perchlorate (GFM = 138.6 g/mol):
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Calculate the moles:
[ \text{Moles} = \frac{5.5 ext{ g}}{138.6 ext{ g/mol}} \approx 0.0397 ext{ moles} ]
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Determine the energy released per mole:
[ \text{Energy per mole} = \frac{103 ext{ kJ}}{0.0397 ext{ moles}} \approx 2,593.4 ext{ kJ/mol} ]
Thus, the energy released per mole of potassium perchlorate is approximately 2,593.4 kJ/mol.
Step 5
Explain fully why increasing temperature increases the rate of a chemical reaction.
Answer
Increasing the temperature of a reaction generally increases the rate of the reaction due to several factors:
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Increased Kinetic Energy: Higher temperatures result in greater average kinetic energy among the reacting molecules. This higher energy means that a larger fraction of molecules will possess sufficient energy to overcome the activation energy barrier, leading to more frequent reactions.
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More Frequent Collisions: Increased temperature also causes molecules to move faster and collide more often, increasing the likelihood of achieving successful collisions that lead to reactions.
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Increased Number of Effective Collisions: As temperature rises, not only does the frequency of collisions increase, but so does the energy of those collisions, resulting in a higher probability of reaction.
In conclusion, as the temperature increases, the combination of increased kinetic energy and the frequency of molecular collisions work together to raise the reaction rate.
Step 6
Suggest the metal responsible for peak B on the spectrum.
Answer
Given that peak A has a wavelength of 620 nm, which corresponds to red light, we need to consider common metals used in fireworks that typically emit a distinct color spectrum. The metal responsible for peak B on the spectrum is likely to be Sodium, as it is known to produce a yellow flame and emits light in a similar wavelength range.