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What is the Empirical Formula for this?

A compound, T, contains 41.0 % potassium, 33.7 % sulfur and 25.3 % oxygen by mass. What is the empirical formula of T?[Ar: K, 39; S, 32; O, 16]
Reply 1
Avatar for alow
alow
19
What have you tried?
Reply 2
Avatar for zattyzatzat
zattyzatzat
OP
9
Original post by alow
What have you tried?


I used the method which i was taught in school. Divide the percentage of mass of each element by it's atomic number. Then divide that the results with the smallest outcome. And then that is the amount of atoms for each element. so:

K:41/39 = 1.0512
S:33.7/32 = 1.0531
O:25.3/ = 1.5812

K:1.0512 / 1.0512 = 1
S:1.0531 / 1.0512 = 1
O:25.3 / 1.0512 = 1.5

Previously when i tried doing empirical formula questions like these. I could do it. But I know this is wrong because of the 1.5 value for oxygen.
Reply 3
Avatar for alow
alow
19
Original post by zattyzatzat
I used the method which i was taught in school. Divide the percentage of mass of each element by it's atomic number. Then divide that the results with the smallest outcome. And then that is the amount of atoms for each element. so:

K:41/39 = 1.0512
S:33.7/32 = 1.0531
O:25.3/ = 1.5812

K:1.0512 / 1.0512 = 1
S:1.0531 / 1.0512 = 1
O:25.3 / 1.0512 = 1.5

Previously when i tried doing empirical formula questions like these. I could do it. But I know this is wrong because of the 1.5 value for oxygen.


http://www.chemspider.com/Chemical-Structure.55421.html
Original post by zattyzatzat
I used the method which i was taught in school. Divide the percentage of mass of each element by it's atomic number. Then divide that the results with the smallest outcome. And then that is the amount of atoms for each element. so:

K:41/39 = 1.0512
S:33.7/32 = 1.0531
O:25.3/ = 1.5812

K:1.0512 / 1.0512 = 1
S:1.0531 / 1.0512 = 1
O:25.3 / 1.0512 = 1.5

Previously when i tried doing empirical formula questions like these. I could do it. But I know this is wrong because of the 1.5 value for oxygen.


If you get half numbers then you multiply all of them by the smallest number that will take them all to whole numbers:

K: 1 X 2 = 2
S: 1 X 2 = 2
O: 1.5 X 2 = 3
Original post by Plantagenet Crown
If you get half numbers then you multiply all of them by the smallest number that will take them all to whole numbers:

K: 1 X 2 = 2
S: 1 X 2 = 2
O: 1.5 X 2 = 3


"divide"
Original post by charco
"divide"


Once you have done the calculations and are down to the final numbers you most certainly can multiply to get rid of non integers. After all, multiplying 1,1,1.5 by 2 is exactly the same as dividing 1,1,1.5 by 0.5 and the multiplication is often easier to see.

https://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm
Original post by Plantagenet Crown
Once you have done the calculations and are down to the final numbers you most certainly can multiply to get rid of non integers. After all, multiplying 1,1,1.5 by 2 is exactly the same as dividing 1,1,1.5 by 0.5 and the multiplication is often easier to see.

https://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm


carbon 81.82%
hydrogen 18.18%

C: 81.82/12 = 6.82
H: 18.18/1 = 18.18

What are you going to multiply by?
Original post by Plantagenet Crown
Once you have done the calculations and are down to the final numbers you most certainly can multiply to get rid of non integers. After all, multiplying 1,1,1.5 by 2 is exactly the same as dividing 1,1,1.5 by 0.5 and the multiplication is often easier to see.

https://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm


Phosphorus: 43.66%
Oxygen: 56.34%

P: 43.66/31 = 1.41
O: 56.34/16 = 3.52

What are you going to multiply by?
Original post by charco
Phosphorus: 43.66%
Oxygen: 56.34%

P: 43.66/31 = 1.41
O: 56.34/16 = 3.52

What are you going to multiply by?


Original post by charco
carbon 81.82%
hydrogen 18.18%

C: 81.82/12 = 6.82
H: 18.18/1 = 18.18

What are you going to multiply by?


I was referring to the part of the calculation when you get the FINAL numbers, in the example given by the OP 1, 1, 1.5, not immediately after dividing the percentage by the atomic mass.
(edited 7 years ago)
With this Oxygen and Phosphorus one, you can see straight away that both 1.41 and 3.52 are just about multiples of 0.7.

1.4/0.7 = 2
3.5/0.7 = 5

Also you know that O has 6 electrons in outer shell, so can gain or share two and P has 5, so can lose or share 5 (or 3).

So you can work out that the answer is P2O5

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