An organic compound contains #45.90%# #C#; #2.75%# #H#; #7.65%# #N#; #17.50%# #S#; and the balance oxygen. What is the empirical formula of the compound?
The empirical formula is
First, list all of your elements. In this case they are carbon, hydrogen, oxygen, sulphur and nitrogen.
Assume that you have 100g of this compound. Consequently, you can assume that you have in grams the percentage you are given for each element. For example, you can assume that you have 45.9g of carbon, 2.75g of hydrogen, and so on.
Now, you get out your periodic table and look for the
#A_r#of each element. For carbon it's 12.01, hydrogen is 1.01 and so on.
Find the number of moles you have for of each element. You do this by dividing the mass in grams by the
#A_r#for each element. So, we have:
#45.9/12.01=3.82#moles of carbon,
- Lastly, you just have to divide all of the values we just calculated by the smallest number of moles that there was. So in this case the smallest is 0.55. I have rounded the numbers to integers because they have to be integers in chemical compounds. For instance, you can't have 2.5 atoms.
So the empirical formula is
We get an empirical formula of
As with all these problems, we assume a mass of
And now we divide thru by the smallest molar quantity, that of nitrogen, and sulfur. We do this to normalize the result:
Note that normally we would not be given a percentage oxygen content (why not? because oxygen is experimentally hard to measure); we would calculate the
And thus we get an empirical formula of
Good question. I am stealing it for my A2 class.