Empirical and Molecular Formulas

Ramneet Sandhu 3D
Posts: 50
Joined: Fri Aug 30, 2019 12:16 am

Empirical and Molecular Formulas

This is a pretty general question, but how do you know how to tell whether you are given an empirical formula or a molecular formula in a problem?

Posts: 51
Joined: Sat Sep 07, 2019 12:19 am

Re: Empirical and Molecular Formulas

The molar mass of the molecule will be given if you are to find the molecular formula.

Chloe Alviz 1E
Posts: 102
Joined: Sat Aug 17, 2019 12:17 am

Re: Empirical and Molecular Formulas

Typically, the empirical formula can be found when you are given the mass of each element present in the sample (ex. a sample of a compound has 4.75 g C, 2.03 g N and 8.24 g O) or the mass percent composition of a molecule (ex. if you were told you had 43% C, 37% H and 20% O in a given sample) With this information you can find the number of moles present in each element and compare from there.

If you are asked for the molecular formula, they will provide you its molar mass. You first have to find the molar mass of the empirical formula so you can find the ratio between the two (divide the molecular molar mass / empirical molar mass). You then multiply each subscript in the empirical formula by this number to get your molecular formula.

Ian Morris 3C
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Joined: Wed Sep 18, 2019 12:18 am

Re: Empirical and Molecular Formulas

I find the easiest way to remember is just to think of molar mass first whenever I hear molecular formula.

Posts: 103
Joined: Sat Aug 24, 2019 12:15 am

Re: Empirical and Molecular Formulas

As Lavelle had said in the lecture, the molar mass will be given if it is asking to distinguish between the molecular and empirical formulas. To decide which is which, you would need to find the molar mass of the formula on hand and compare it to the given molar mass of the substance on hand. If they are equal, you have the molecular formula, but if the given molar mass is more, then you likely have the empirical formula and need to add a subscript to multiply the atoms to match the molar mass of the given substance.

Sally kim 4F
Posts: 53
Joined: Thu Jul 25, 2019 12:17 am

Re: Empirical and Molecular Formulas

Referring to Lavelle's first module, the empirical formula shows the relative number of atoms that a molecule has, and the molecular formula shows the actual number of atoms. By this, we can understand that the empirical formula is the simplest ratio of the elements. Therefore, if the formula given can be reduced, it most likely will be the molecular formula.

Kylie Lim 4G
Posts: 110
Joined: Sat Aug 17, 2019 12:15 am

Re: Empirical and Molecular Formulas

The empirical formula is the smallest integer ratio of atoms in a compound. If you calculate the molar mass for the basic compound and it is smaller than the given molar mass, you know that the empirical and molecular formulas are different.

erica thompson 4I
Posts: 55
Joined: Wed Sep 18, 2019 12:21 am

Re: Empirical and Molecular Formulas

In the simplest terms, the empirical formula is the relative number of atoms, while the molecular formula is the actual number of atoms.

Emily Chirila 2E
Posts: 112
Joined: Sat Jul 20, 2019 12:16 am

Re: Empirical and Molecular Formulas

Compare the formula to the given molar mass. It is also possible it could be both the empirical and the molecular formula if the molar masses match up!

Erik Buetow 1F
Posts: 96
Joined: Fri Aug 30, 2019 12:15 am

Re: Empirical and Molecular Formulas

Empirical formulas can be the same as molecular formulas, but in general, an empirical formula gives the simplified ratio of the molecules present rather than the actual formula for a given compound.

VPatankar_2L
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Joined: Thu Jul 25, 2019 12:17 am
Been upvoted: 1 time

Re: Empirical and Molecular Formulas

Generally if you're given a molecular formula, you will be able to reduce the number of moles of each element by a certain factor. If you're given an empirical formula, you can't divide by a number to reduce the umber of moles of the element in the formula.

alexfwang3g
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

Re: Empirical and Molecular Formulas

If the total molar mass of the molecular formula coincides with the empirical formula, then the empirical formula is the molecular formula. Otherwise, the empirical formula is just a ratio in the form of the lowest possible whole numbers of a molecule. The molecular formula is the actual molecule and should match with the molecular mass that's given for the molecule.

annikaying
Posts: 94
Joined: Sat Sep 14, 2019 12:16 am

Re: Empirical and Molecular Formulas

If you are given a formula and a given mass you can calculate the molar mass of the compound and see if the two masses are equal. If they are equal then the given formula is empirical. If not, then it is a molecular formula. You also may be able to tell by checking if the ratios are all in their smallest form.

mayarivers3I
Posts: 52
Joined: Wed Sep 18, 2019 12:18 am

Re: Empirical and Molecular Formulas

If the problem gives you the molar mass of the compound, then you can find the molar mass of the formula that's given and compare that to the given mass, and if it's the same, then that's the molecular formula, otherwise it is the empirical formula.