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Going from empirical to Molecular formula

Posted: Mon Oct 08, 2018 3:10 pm
by Daniela Alvarado 3B
When trying to find the molecular formula & we put the molar mass of molecular formula over the mass of the empirical formula we found, is the number supposed to be a whole # or can it be like 1.23? If it can be 1.23, do we round when we multiply it by the subscript of the elements in empirical formula??

Re: Going from empirical to Molecular formula

Posted: Mon Oct 08, 2018 3:16 pm
by Chem_Mod
The molecular formula should be complete multiples of the empirical formula, or very close to whole numbers. The questions should be designed so that there is little ambiguity.

Re: Going from empirical to Molecular formula

Posted: Mon Oct 08, 2018 3:23 pm
by rosemarywang4i
If the number were 1.23, I would try multiplying everything by a factor of 4 or 5 to get closer to a whole number. See which seems to work better for the other coefficients!

Re: Going from empirical to Molecular formula

Posted: Mon Oct 08, 2018 3:46 pm
by Ethan Yi 1K
the molecular formula will be an exact multiple of the empirical. So the molar mass of the molecular formula divided by the molar mass of the empirical should turn out to be a whole number.

Re: Going from empirical to Molecular formula

Posted: Tue Oct 09, 2018 5:43 pm
by Hannah Morales 1D
Yeah, it should be a whole number when you multiple it. If you get a decimal of some sort I believe it should be so close to a whole number value. Ex: 4.98-5.01 (would round up or round down respectively to get 5)

Re: Going from empirical to Molecular formula

Posted: Tue Oct 09, 2018 6:44 pm
by Zubair Ahmed 1L
Yea, it should be a whole number. The questions are usually phrased in a way in which the multiple of of the molecular to empirical formula is easy to work with. However, there may be examples where the multiple is "3.99" or "4.02". In this case, you would round to the nearest whole number.

Re: Going from empirical to Molecular formula

Posted: Tue Oct 09, 2018 9:18 pm
by Sophia Fox 4B
The factor that you get after dividing the molecular mass by the empirical mass should be an integer, or really close (I think if you can round from the hundredths place to an integer it's close enough). If you don't get an integer than re-check the empirical formula or empirical mass. It's really easy to type something in wrong on your calculator and mess up the whole problem!!

Re: Going from empirical to Molecular formula

Posted: Sat Oct 13, 2018 9:23 pm
by KHuang1L
It should be a whole number. First check to make sure that your work leading up to the empirical formula is correct.

Re: Going from empirical to Molecular formula

Posted: Sat Oct 13, 2018 11:11 pm
by Abhi4F
The value should be close to a whole number or if not very close so you can round to one.

Re: Going from empirical to Molecular formula

Posted: Sat Oct 13, 2018 11:18 pm
by Brandon Sanchez 3J
When you divide the mass of the molecular formula by the mass of the empirical formula, you should get a whole number. Or the number could at least be in the #.98-#.00 range.

Re: Going from empirical to Molecular formula

Posted: Sun Oct 14, 2018 12:57 am
by daniela3D
The video modules he has posted on his websites are very helpful. For this question he explains why there has to be a whole number for the empirical formula and if you multiply one number you have to do the same to the rest. Highly recommend if you have not checked it out.

Re: Going from empirical to Molecular formula

Posted: Sun Oct 14, 2018 10:14 pm
by Joussie Camacho 4I
How do you go from the molecular formula to the empirical formula if you aren't given a molar mass by mass spectrometry to compare to (and divide by) the molar mass you calculate using the molecular formula? In other words, how would we know what factor the empirical formula was multiplied by in order to get to the molecular formula?

Re: Going from empirical to Molecular formula

Posted: Thu Nov 15, 2018 11:41 pm
by 705022748
The number should be a whole number, but if it isn't and it's really close you can round it up.

Re: Going from empirical to Molecular formula

Posted: Sun Dec 09, 2018 11:26 pm
by uhedlund
The number should be a whole number; if you get a fraction and have checked your work, multiply all by a number to give you whole numbers.

Re: Going from empirical to Molecular formula

Posted: Sun Dec 09, 2018 11:32 pm
by 405021651
The molecular formula can still be divided down to get simpler values while the empirical can not be