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# Empirical formula question Watch

1. Hi guys,

Just wondering whether someone could check I'm doing this right as I haven't done it in well over a year!

The question asks me to find the empirical formula of a compound which is given to us as percentage by mass.
The first one is 47% Nitrogen and 53% Oxygen

Am I right by doing 16 x 0.53 = 8.48
and 14 x 0.47= 5.58

And then would I multiply them both by 2 to get approximate whole numbers for the formula?

Thanks
Blake
2. (Original post by Blake Jones)
Hi guys,
Just wondering whether someone could check I'm doing this right as I haven't done it in well over a year!
The question asks me to find the empirical formula of a compound which is given to us as percentage by mass.
The first one is 47% Nitrogen and 53% Oxygen
Am I right by doing 16 x 0.53 = 8.48
and 14 x 0.47= 5.58
And then would I multiply them both by 2 to get approximate whole numbers for the formula?
Thanks
Blake
Assuming this is GCSE/A-level standard
The way I was taught is to divide the percentage by mass by the Ar
Therefore, separately doing: (Nitrogen Ar=14) = 47/14 and (Oxygen Ar=16) = 53/16
I get 3.36 (2.d.p) and 3.31 (2.d.p) respectiveley
Then you divide the bigger by the smaller
Therefore I will divide 3.36 by 3.31 (and also 3.31 by 3.31 = 1)
The number I get out of it is N = 1.035 and O=1
Therefore the Empirical formula = NO
3. (Original post by CheeseIsVeg)
Assuming this is GCSE/A-level standard
The way I was taught is to divide the percentage by mass by the Ar
Therefore, separately doing: (Nitrogen Ar=14) = 47/14 and (Oxygen Ar=16) = 53/16
I get 3.36 (2.d.p) and 3.31 (2.d.p) respectiveley
Then you divide the bigger by the smaller
Therefore I will divide 3.36 by 3.31 (and also 3.31 by 3.31 = 1)
The number I get out of it is N = 1.035 and O=1
Therefore the Empirical formula = NO
Ah yep, that rings a bell and makes more sense, thanks!
4. (Original post by Blake Jones)
Ah yep, that rings a bell and makes more sense, thanks!
np
fingers crossed I didnt mess it up lol
good luck!
5. (Original post by CheeseIsVeg)
np
fingers crossed I didnt mess it up lol
good luck!
Haha! It looks better than the answer I got anyhow! XD Thanks!
6. (Original post by Blake Jones)
Hi guys,both by 2 to get approximate whole numbers for the formula?... Thanks Blake
(Original post by CheeseIsVeg)
Assuming this is... Empirical formula = NO
The suggested method seems sensible

Just so you know/ understand the chemistry you do Mass/Ar to work out the moles in order to know the mole to mole ratio between elements and the divide by the smallest mole value in order to find the simplest whole number ratio between them.

Just thought i'd add that for understanding seeming AS/A2 require understanding and not just mathematical methods

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