[JayEm]

Can someone please help me with the following calculations, I have the answers but don't understand how they are obtained:

1. "The minimum mass of aluminium needed to displace 1000g of iron from an excess of iron(II) oxide is...."

Answer = 484g

2. "A particular sample of bauxite ore contains 55% by mass of Al₂O₃ (Mr=102) and no other aluminum compound. The minimum mass of this ore needed to produce 1.0 tonne of aluminium is..."

Answer = 3.4 tonne

Any help would be greatly appreciated.
Thanks in advance.

[Borek]

Start with reaction equations. Or at least - if you don't know exact reaction equations - try to outline them writing important information.

[Albert]

Can someone please help me with the following calculations, I have the answers but don't understand how they are obtained:

1. "The minimum mass of aluminium needed to displace 1000g of iron from an excess of iron(II) oxide is...."

Answer = 484g

Are you sure it's not iron III oxide?

[Dan]

Yeah, it must be Iron (III) oxide.

Step 1. Write a balanced equation
Step 2. Work out how many moles of Iron are in 1000g of Iron, let's call that value 'X'.
Step 3. Look at your balanced equation. How many moles of Al react to give one mole of Iron?

           In that case, how many moles of Al react to give you the X moles of Iron from step 2? That is how many moles of Al you need.
Step 4. What is the mass of that number of moles of Al?
           If you've got it right, your answer should be close to 484g.

I did this calculation using relative atomic masses Fe = 56 and Al = 27, and I got 482g

[Albert]

For question number 2, you can use this equation:

Al₂O₃.H₂O(s) + 2 OH^- + 2 H₂O -> 2 [Al(OH)₄]^-

[Dan]

For question 2, this would be my method.

Step 1. How many moles of Al are in 1 tonne of Al?
Step 2. How many moles of Al2O3 can this produce? (Hint: write a balanced equation for the formation of Al2O3 from Al and O2)
Step 3. What is the mass of that number of moles of Al2O3?
Step 4. That mass (from step 3) is 55% of the mass of the Bauxite you need. What is 100% of the mass of the bauxite you need?

Hint: 0.55x(Mass of bauxite you need) = "55% of the mass of Bauxite you need"