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# Basic question about reacting quantities ? watch

1. Just wondering if someone could show me how to work out the following two questions ?

1) Find the empirical formula of the following
a) Sodium Oxide (2.3g of sodium reacts to form 3.1g of sodium oxide)
b)Iron Oxide (11.16g of iron reacts to form 15.96g of Iron Oxide)

I have the answers but no working out if anyone could help it would be greatly appreciated .

Kind regards

Sunny
2. All you're doing is working out the ratio of one element to another in a compound.
For a) work out how many moles of Na there is which = 2.3/23 = 0.1 mol.
For oxygen you have (3.1-2.3)/16 = 0.05 mol.
So for every 2 moles of Na there is 1 mole of oxygen. So empirical formula is .
Why don't you use this and try the next one for yourself.
3. Thank you so much
4. (Original post by B_9710)
All you're doing is working out the ratio of one element to another in a compound.
For a) work out how many moles of Na there is which = 2.3/23 = 0.1 mol.
For oxygen you have (3.1-2.3)/16 = 0.05 mol.
So for every 2 moles of Na there is 1 mole of oxygen. So empirical formula is .
Why don't you use this and try the next one for yourself.
Thank you very much but here is where I'm stuck for question b)

b) First we work out how many moles of Fe = 11.2/55 = 0.2 moles
Then for Oxygen = 15.96-11.2 = 4.74g/16 = 0.3 moles

So where do I go from here ... ??

again any help is greatly appreciated .
5. (Original post by parmar263)
Thank you very much but here is where I'm stuck for question b)

b) First we work out how many moles of Fe = 11.2/55 = 0.2 moles
Then for Oxygen = 15.96-11.2 = 4.74g/16 = 0.3 moles

So where do I go from here ... ??

again any help is greatly appreciated .
The answer in the book is Fe2 O3 , I can't understand how they come to that calculation ?
6. (Original post by parmar263)
Thank you very much but here is where I'm stuck for question b)

b) First we work out how many moles of Fe = 11.2/55 = 0.2 moles
Then for Oxygen = 15.96-11.2 = 4.74g/16 = 0.3 moles

So where do I go from here ... ??

again any help is greatly appreciated .
The ratio of oxygen:iron is 0.2:0.3 right?
But multiplying by 10 that ratio is the same as 2:3 right?
So for every 3 oxygen ions there are 2 iron ions (forget about the fact that they're ions as it doesn't not affect the calculation at all, I'm just saying it as that is its actual structure).

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