Empirical formula question ?
Ok do when you are given a percent lets say 5% , 10% and 15% of certain elements and you are supposed to assume there is 100 grams of that element to easily convert it to grams . My teacher said just to move the decimal twice and I used those as the subscripts but I have seen people just write the same exact thing without decimals and just straight into grams (khan academy) . Okay so I still get the right answer but what is the correct / right way to do it ?
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Verified answer
I do what you report Khan Academy does. I do not waste my time by saying something like -
Consider that you have 100g of compound
Then you have so many g of each element.
I go straight in using the % values.
For example :
What is the empirical formula for a compound with the following % composition :
Carbon 40.00 %
Hydrogen 6.71%
Oxygen 53.29 %
At the most , I check that the % values total 100% - if not go no further - problem has an error
Step 1: divide each % value by the respective atomic mass of the element
C = 40.00/12 = 3.33
H = 6.71/1 = 6.71
O = 53.29/16 = 3.33
Divide by smallest value
C = 3.33/3.33 = 1
H = 6.71/3.33 = 2
O = 3.33/3.33 = 1
Empirical formula = CH2O.
I do not waste my time - or that of my students by stating that I take 100g of compound and then , in the case above I have 40.00gC carbon , etc.
hey there ! the correct way is to
* first convert percent into grams by ÷ by 100
* once you have the grams divide that by the molar mass of the element in question to get the moles
* once you have all the moles look for the smallest value of the moles
* now divide the rest by the smallest value to get the subscript values ( round them off if needed)
*and thats it !!