APersonYo
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A student uses 1.00 g of iron (III) oxide and makes on crystallisation 0.450 g of sodium ferrate (VI), Na2FeO4

Calculate the percentage yield by mass of sodium ferrate

The mark scheme says this...

Mr of Fe2O3= 159.6

Mr of Na2FeO4= 165.8
Moles of Fe2O3= 0.00627

Mass of Na2FeO4= 2.08

Therefore percentage purity is 21.6 or 21.7

But I dont understand how these components are related to finding the answer?
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milkm4n
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  • since iron (III) oxide [Fe2O3] has 2 moles of iron for every molecule where sodium ferrate (VI) has 1 mole for every molecule, the ratio of

iron oxide : sodium ferrate = 1:2 (since the no. of moles of iron must be equal on either side of the equation)
  • % yield = 100(actual yield/theoretical yield)
  • since moles of Fe2O3 = mass/Mr = 1/159.6, (theoretical) moles of sodium ferrate = 2 * (1/159.6) = 0.0125...
  • Therefore (theoretical) mass of sodium ferrate = Mr * moles = 165.8 * 0.0125... = 2.0776... g
  • Therefore % yield = 100(0.450/2.0776...) = 21.7% (3sf)


Edit: The first step is the hardest part of the question to understand. You could write down a balanced symbol equation to find the molar ratio of (iron oxide : sodium ferrate) however this method works as well
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APersonYo
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(Original post by milkm4n)
  • since iron (III) oxide [Fe2O3] has 2 moles of iron for every molecule where sodium ferrate (VI) has 1 mole for every molecule, the ratio of

iron oxide : sodium ferrate = 1:2 (since the no. of moles of iron must be equal on either side of the equation)
  • % yield = 100(actual yield/theoretical yield)
  • since moles of Fe2O3 = mass/Mr = 1/159.6, (theoretical) moles of sodium ferrate = 2 * (1/159.6) = 0.0125...
  • Therefore (theoretical) mass of sodium ferrate = Mr * moles = 165.8 * 0.0125... = 2.0776... g
  • Therefore % yield = 100(0.450/2.0776...) = 21.7% (3sf)


Edit: The first step is the hardest part of the question to understand. You could write down a balanced symbol equation to find the molar ratio of (iron oxide : sodium ferrate) however this method works as well
How do you even know this???

since iron (III) oxide [Fe2O3] has 2 moles of iron for every molecule where sodium ferrate (VI) has 1 mole for every molecule, the ratio of
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