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Interpretation: The mass of iron (III) oxide produced on heating 1.25 g of iron and 0.0204 mole of oxygen gas needs to be calculated.
Concept introduction: The ratio of the mass of a substance to its molar mass is said to be the number of moles of that substance.
Answer to Problem 40A
The mass of iron (III) oxide produced on heating 1.25 g of iron and 0.0204 mole of oxygen gas is 1.76 g .
Explanation of Solution
The chemical equation for the formation of iron(III) oxide from iron and oxygen gas is:
Fe(s) + O2(g)→Fe2O3(s)
The above reaction is not balanced as the number of atoms of Fe and O is 1 and 2 on the reactant side and 2 and 3 on the product side.So in order to balance the reaction, coefficient 4 and 3 are written before Fe and O2 respectively on the reactant side and coefficient 2 is written before Fe2O3 on the product side. Thus, the balanced equation is:
4Fe(s) + 3O2(g)→2Fe2O3(s)
The mass of iron (III) oxide produced will be calculated after determining the limiting reagent (The reagent in a reaction that controls the amount of product formed is termed as limiting reagent. After completion of
Calculating the moles of iron as:
Number of moles=MassMolar mass
The molar mass of iron is 55.845 g/mol. The number of moles of ironwill be:
nFe=1.25 g55.845 g/molnFe=0.022 mol
The given mole of oxygen gas is 0.0204 mol.
In the above-balanced reaction, 4.0 mol of Fe reacts with 3.0 mol of O2 . So, the number of moles of Fe required to react with 0.0204 mol of O2 is:
0.0204 mol of O2×4 mol of Fe3 mol of O2 = 0.0272 mol of Fe
Since, the required moles of Fe is 0.0272 mol and the available amount is 0.022 mol , so Fe is the limiting reactant and O2 is present in excess. So, the amount of iron(III) oxide formed will depend on the number of moles of Fe :
From the balanced chemical reaction, the mole ratio of Fe and iron(III) oxide is 4:2 so, the number of moles of water iron(III) oxide from 0.022 mol of Fe is:
0.022 mol of Fe×2 mol of Fe2O34 mol of Fe = 0.011 mol of Fe2O3
Now, the mass of iron(III) oxide produced is calculated as:
The molar mass of iron(III) oxide is 159.69 g/mol. So,
Number of moles=MassMolar mass0.011 mol=Mass159.69 g/molMass = 0.011 mol×159.69 g/molMass = 1.76 g
Hence, the mass of iron (III) oxide produced on heating 1.25 g of iron and 0.0204 mole of oxygen gas is 1.76 g .
Chapter 9 Solutions
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