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### Identifying Empirical and Molecular Formulas

Posted: Sun Jul 02, 2017 12:25 pm
What are the differences between the Molecular and Empirical formulas? More specifically, how do you identify one from the other?

### Re: Identifying Empirical and Molecular Formulas  [ENDORSED]

Posted: Sun Jul 02, 2017 12:43 pm
The molecular formula shows the actual number of atoms while the empirical formula shows the simplest atomic ratio. In order to figure out if its an empirical or molecular formula you would have to calculate the molar mass of the formula you have and also be given the molar mass (from mass spectrometry). If the molar mass you calculated and the molar mass you were given are equal then it's the molecular formula. Hope this makes sense!

### Re: Identifying Empirical and Molecular Formulas

Posted: Sun Jul 02, 2017 7:49 pm
The empirical formula is the formula that shows the ratio of atoms. The molecular formula shows the actual number of atoms. An example would be CH2O. This is the empirical formula for glucose, which is C6H12O6. You can see that for every one atom of C, there are two of H and one of O. This is given in the empirical formula.

It's important to remember that the empirical formula can also be the molecular formula. For example, CH2O is the empirical and molecular formula for formaldehyde (according to Google). You wouldn't know if an empirical formula is the molecular formula unless you are given the molar mass of the whatever you are analyzing.

### Re: Identifying Empirical and Molecular Formulas

Posted: Wed Oct 04, 2017 12:22 pm
An empirical formula is just the ratio of the atoms in a reaction, whereas an molecular formula shows the actual number of atoms in a reaction. In order to calculate a molecular formula, you first must calculate the empirical formula by dividing the given mass by the molar mass to find the amount of moles. The actual molar mass would be given. Divide the given mass by the molar mass of the empirical formula to find the molecular formula.

### Re: Identifying Empirical and Molecular Formulas

Posted: Wed Oct 04, 2017 3:01 pm
104730551 wrote:What are the differences between the Molecular and Empirical formulas? More specifically, how do you identify one from the other?

I have a similar additional question to add to this post. When doing a problem, what is the best way to realize if I have found the molecular or empirical formula? Sometimes I get the two confused, and I was wondering if there is a simple way for me to define/see the difference between the two.

### Re: Identifying Empirical and Molecular Formulas

Posted: Wed Oct 04, 2017 3:38 pm
Sydney Briggs 1B wrote:
104730551 wrote:What are the differences between the Molecular and Empirical formulas? More specifically, how do you identify one from the other?

I have a similar additional question to add to this post. When doing a problem, what is the best way to realize if I have found the molecular or empirical formula? Sometimes I get the two confused, and I was wondering if there is a simple way for me to define/see the difference between the two.

The empirical formula will always be the formula that is more simplified. If you have a formula that can be further reduced into it's basic ratio, then you have the molecular formula. So basically you know you have the empirical formula when you can't divide the numbers by a common variable and you have a molecular formula when you can.

Also, problems are usually in order of what you're trying to find. Normally you have to have the empirical formula and molar mass of the compound to determine the molecular formula, so if there's a problem where you have to find both the empirical and molecular formula, usually the first formula you find is the empirical formula.

### Re: Identifying Empirical and Molecular Formulas

Posted: Wed Oct 04, 2017 9:14 pm
Empirical formula just gives the ratio/relative number of atoms
The molecular formula gives the actual number of atoms.
So the empirical formula would usually have a smaller ratio than the molecular formula
ex) C3H4O3 <-- empirical
C6H8O6 <-- molecular

### Re: Identifying Empirical and Molecular Formulas

Posted: Wed Oct 04, 2017 9:51 pm
When writing an empirical or molecular formula, how do you know in what order to write the elements? For example, how would you know to write Na3AlF6 rather than AlNa3F6 or Na3F6Al?

### Re: Identifying Empirical and Molecular Formulas

Posted: Wed Oct 04, 2017 10:05 pm
104730551 wrote:What are the differences between the Molecular and Empirical formulas? More specifically, how do you identify one from the other?

The empirical formula is the ration of atoms of a compound while the molecular is the actual number of atoms. For example, in a room of children there is 20 boys and 25 girls. while the ration of boys to girls is 4:5, the actual number of boys to girls is 20:25.

### Re: Identifying Empirical and Molecular Formulas

Posted: Thu Oct 05, 2017 4:28 pm
Marcela Luna IJ wrote:When writing an empirical or molecular formula, how do you know in what order to write the elements? For example, how would you know to write Na3AlF6 rather than AlNa3F6 or Na3F6Al?

Our discussion asked that exact same question today, and our T.A told us that generally, the metal atom goes first followed by the rest. But he also said that most of the time, it doesn't matter in what order they are written. Different books have different orders, so as long as the formula is right the order doesn't really matter. He also stated that he wouldn't take points away if its not written in the "correct" order.

### Re: Identifying Empirical and Molecular Formulas

Posted: Thu Oct 05, 2017 4:42 pm
The empirical formula shows the relative numbers of atoms of each element present in the compound (It is the simplest positive integer ratio of atoms present in a compound)
The molecular formula shows the actual numbers of atoms of each element in a molecule

### Re: Identifying Empirical and Molecular Formulas

Posted: Fri Oct 06, 2017 12:24 am
If you are asked to find the empirical formula and are given a set of atoms along with their mass in grams, can you use those numbers to find the empirical formula without finding the mass percentage composition? Or do you always have to find the mass percent composition before finding the empirical formula?

### Re: Identifying Empirical and Molecular Formulas

Posted: Fri Oct 06, 2017 12:54 am
Marcela Luna IJ wrote:When writing an empirical or molecular formula, how do you know in what order to write the elements? For example, how would you know to write Na3AlF6 rather than AlNa3F6 or Na3F6Al?

When writing the molecular or empirical formula the order usually is the elements C followed by H, and then it always ends with O. If there are other elements, it should always be in alphabetical order from what I've learned! So the correct order for your example is AlF6NA3!

### Re: Identifying Empirical and Molecular Formulas

Posted: Fri Oct 06, 2017 3:12 pm
The way that I remember that empirical refers to the ratio of atoms and that molecular refers to the exact number is that empirical measurements like feet and inches are less commonly used globally and usually needs to be converted to be used in most formulas and to me in empirical isn't the most complete form of the molecule as it doesn't tell you the most data.