Odd chemistry question?Watch

Announcements
Thread starter 2 years ago
#1
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?
1
2 years ago
#2
• 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
0
Thread starter 2 years ago
#3
(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
0
X

new posts Back
to top
Latest
My Feed

Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

University open days

• University of Surrey
Wed, 23 Oct '19
• University of Bristol
Wed, 23 Oct '19
• University of Exeter
Undergraduate Open Day - Penryn Campus Undergraduate
Wed, 23 Oct '19

Poll

Join the discussion

Yes (36)
25.71%
No (104)
74.29%