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A mixture of potassium nitrate and sulfur reacts according to the following balanced equation - Leaving Cert Chemistry - Question a - 2016
Question a
A mixture of potassium nitrate and sulfur reacts according to the following balanced equation. $$4KNO_3 + 5S \rightarrow 2K_2O + 2N_2 + 5SO_2$$ One of the two reac... show full transcript
Worked Solution & Example Answer:A mixture of potassium nitrate and sulfur reacts according to the following balanced equation - Leaving Cert Chemistry - Question a - 2016
Step 1
Which reactant is in excess?
Answer
To determine which reactant is in excess, we need to first calculate the moles of each reactant:
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Calculate Moles of Potassium Nitrate (KNO₃):
Molar mass of KNO₃ = 101 g/mol.
Moles of KNO₃ = ( \frac{20.2 \text{ g}}{101 \text{ g/mol}} \approx 0.2 \text{ moles} ) -
Calculate Moles of Sulfur (S):
Molar mass of S = 32 g/mol.
Moles of S = ( \frac{24.0 \text{ g}}{32 \text{ g/mol}} = 0.75 \text{ moles} ) -
Determine the Stoichiometry from the Balanced Equation:
According to the balanced equation, 4 moles of KNO₃ react with 5 moles of S. Thus, the ratio is ( \frac{4}{5} ). Therefore, 1 mole of KNO₃ requires ( \frac{5}{4} ) moles of S. For 0.2 moles of KNO₃: ( 0.2 \text{ moles KNO₃} \times \frac{5}{4} = 0.25 \text{ moles S required} ) -
Compare Required Moles of S with Available Moles:
Available moles of S = 0.75 moles, which is greater than 0.25 moles required. Hence, KNO₃ is the limiting reactant and S is in excess.
Step 2
What mass of this reactant is unused at the end of the reaction?
Answer
To find the unused mass of sulfur (S):
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Calculate Unused Moles of S:
Moles of S initially = 0.75 moles.
Moles of S used = 0.25 moles (as calculated).
Therefore, unused moles of S = ( 0.75 - 0.25 = 0.50 \text{ moles} ) -
Convert Unused Moles to Mass:
Mass of unused S = ( 0.50 \text{ moles} \times 32 \text{ g/mol} = 16 ext{ g} )
Thus, the mass of sulfur that is unused is 16 g.
Step 3
Calculate the total volume (in litres) of gaseous products, measured at s.t.p., formed in the reaction.
Answer
Using the stoichiometry from the balanced equation, we can determine the volume of gases produced:
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Identify Gaseous Products:
Gaseous products in the reaction: 2N₂ + 5SO₂. Total moles of gas produced = 2 + 5 = 7 moles. -
Calculate Volume at Standard Temperature and Pressure (STP):
At STP, 1 mole of any gas occupies 22.4 litres. Volume of gas = ( 7 \text{ moles} \times 22.4 \text{ litres/mole} = 156.8 \text{ litres} )
Therefore, the total volume of gaseous products is 7.84 litres.
Step 4
What mass of solid is produced?
Answer
To find the mass of solid produced from the reaction:
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Identify Solid Product:
The only solid product in this reaction is potassium oxide (K₂O). -
Calculate Moles of Solid K₂O Produced:
From balanced equation, 4 moles of KNO₃ yield 2 moles of K₂O. Thus, 0.2 moles of KNO₃ will yield: ( \frac{2}{4} \times 0.2 = 0.1 \text{ moles K₂O} ) -
Convert Moles to Mass:
Molar mass of K₂O = 94 g/mol.
Mass of K₂O = ( 0.1 \text{ moles} \times 94 \text{ g/mol} = 9.4 ext{ g} )
The mass of solid K₂O produced is 9.4 g.