Which methods to use when finding empirical formulas

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Annika_Karody_3L
Posts: 32
Joined: Fri Sep 25, 2015 3:00 am

Which methods to use when finding empirical formulas

Postby Annika_Karody_3L » Sat Oct 31, 2015 4:18 pm

I am wondering whether our method for finding empirical formulas can differ from that which is shown in the midterm answer keys because the points are assigned to the steps of the method.

For empirical formula problems where we're given the mass of the sample and of each constituent atom, I divide the masses of each constituent atom by their molar masses, then divide those molar masses by the smallest value to get the ratio.

For problems where we're given percentages, I assume a 100g sample and use the percentages of each constituent atoms as masses, divide them by their molar masses and then divide those by the smallest amount of moles to get the ratio.

In the midterm answer keys in course reader, there is an extra step to these methods. In the first situation, we are expected to find the percent composition, assume a 100g sample and then find the moles and mole ratios. In the second situation, we are expected to find the masses of the compounds by multiplying the percentages by the mass of the sample and then find the mole ratios. I am wondering if these methods are required. Thank you!

Jeannie Huang 3B
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Re: Which methods to use when finding empirical formulas

Postby Jeannie Huang 3B » Sun Nov 01, 2015 3:50 pm

I use the same methods as you do for those types of problems, and it wasn't marked incorrect or anything on the first quiz (after all, we arrive at the same answer). So, I assume it's okay to do so.

EPerez1B
Posts: 27
Joined: Fri Sep 25, 2015 3:00 am

Re: Which methods to use when finding empirical formulas

Postby EPerez1B » Tue Nov 24, 2015 9:11 pm

The second method you described is supposed to be more straightforward, so I think it's preferred; however, I don't think it matters which method you use so long as you arrive at the correct answer.


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