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When calculating the empirical formula of a compound and the masses of each element are given, is it necessary to convert the amount of each into a percentage of the actual mass then use the % out of 100g to find the mol ratio, or can you just go from the amounts given to the number of moles of each without calculating Mass Percentage Composition?
Your method is acceptable. Keep in mind that when using mass %, you can easily double check that all of the mass of the sample is accounted for. When you convert mass straight to moles, just make sure that all masses given add up to the total sample mass.
Personally, I like using the 100 g method because if there is such a question that says " there is 40%C, 10%O, 20%H, and an unknown amount of a 4th element, it makes it way easier to go from there inorder to calculate the empirical formula.
No, you do not need to convert the masses of each into percentages when masses are given, unless it asks for mass percent.
Joseph Saba wrote:Personally, I like using the 100 g method because if there is such a question that says " there is 40%C, 10%O, 20%H, and an unknown amount of a 4th element, it makes it way easier to go from there inorder to calculate the empirical formula.
I agree with this, the 100 g method is the easiest because you are able easily convert the percentages into grams.
No, you do not have to, the 100g method just makes it easier to check the work and execute the problem.
If the masses are already given I usually just convert to moles and go from there since it eliminates the extra steps of converting into percentages!
I don't think that you need to use the 100g method but I agree with the above responses that it simplifies the values in the exercise. Say you had an exercise such as F11, where the amount of Oxygen is not stated. Using the 100g method makes it a lot easier to calculate the missing mass of oxygen. With 100g you get 31.91gK, 28.93gCl and (100-60.84)g O. However, the 100g method comes in handy when the masses are not explicit in the exercise, but you need to find the mass percentage composition.
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