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# What is the Empirical Formula for this? Watch

1. 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]
2. What have you tried?
3. (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.
4. (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
5. (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
6. (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"
7. (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/majo.../empirical.htm
8. (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/majo.../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?
9. (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/majo.../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?
10. (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.
11. 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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