Calculating Empirical Formula with Given Amounts of Each Element

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Wilson 2E
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Joined: Sat Aug 17, 2019 12:18 am

Calculating Empirical Formula with Given Amounts of Each Element

Postby Wilson 2E » Thu Oct 03, 2019 4:39 pm

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?

Chem_Mod
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Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby Chem_Mod » Thu Oct 03, 2019 4:44 pm

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.

Joseph Saba
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Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby Joseph Saba » Thu Oct 03, 2019 4:48 pm

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.

KarineKim2L
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Joined: Fri Aug 30, 2019 12:16 am

Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby KarineKim2L » Thu Oct 03, 2019 4:58 pm

No, you do not need to convert the masses of each into percentages when masses are given, unless it asks for mass percent.

abby hyman
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Joined: Thu Jul 25, 2019 12:16 am

Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby abby hyman » Thu Oct 03, 2019 5:20 pm

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.

Nyari Muchaka_Discussion 4A
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Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby Nyari Muchaka_Discussion 4A » Thu Oct 03, 2019 5:22 pm

No, you do not have to, the 100g method just makes it easier to check the work and execute the problem.

zfinn
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Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby zfinn » Thu Oct 03, 2019 5:25 pm

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!

Charlotte Coplon 1K
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Re: Calculating Empirical Formula with Given Amounts of Each Element

Postby Charlotte Coplon 1K » Thu Oct 03, 2019 6:20 pm

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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