Start with the number of grams of each element given in the problem. If percentages are given, assume that the total mass is 100 grams so that the mass of each element is = to the percent given
ex.)60.4% of 100g = 60.4g
Convert the mass of each element to moles using the molar mass(have at least 4 decimal places). Divide each mole value by the smallest number of moles calculated and round to the nearest whole number. This is the mole ratio of the elements and is represented by subscripts in the empirical formula. If the number is too far to round (x.1 ~ x.9), then multiply each solution by the same factor to get the lowest whole number multiple.
i.e.)if one solution is 1.5, then multiply EACH solution in the problem by 2 to get 3. If one solution is 1.25, then multiply each solution in the problem by 4 to get 5.
*you cannot have a fraction of an atom!
Example)NutraSweet is 57.14%C, 6.16%H, 9.52%N, and 27.18%O. Calculate the empirical formula of NutraSweet.
– 57.14g x 1mole/12gC = 4.7617molC
– 6.16gH x 1mole/1gH = 6.16moleH
– 9.52gN x 1mole/14gN = .68molN
– 27.18gO x 1molr/16gO = 1.6988molO
Okay, the smallest mole value that was calculated was .68 moles of Nitrogen. Now divide each mole value by .68 and round to the nearest whole number:
4.7617/.68 = 7 molCarbon
6.16/.68 = 9 molHydrogen
.68/.68 = 1 molNitrogen
1.6988/.68 = 2.5 molOxygen
Since Oxygen was too far to round to a whole number, multiply ALL solutions by 2 to get the lowest whole number:
7 x 2 = 14 molCarbon
9 x 2 = 18 molHydrogen
1 x 2 = 2 molNitrogen
2.5 x 2 = 5 molOxygen
The answer is: C_{14}H_{18}N_{2}O_{5}!
