Molar mass of molecular formulas [ENDORSED]

[Abhinav Amanaganti 3K]

If we are given a question that asks us to find a molecular formula based off an empirical formula, would we be given the molar mass of the compound in question? Ex: We need to find the empirical and molecular formulas of 8 gram of compound X given that the % mass composition is 27% Carbon and 73% Oxygen, once we find the empirical formula will we be provided with the molar mass of compound X in order to determine the molecular formula?

[Devika Nair 2D]

Yes, if you are asked to find the molecular formula from the empirical formula, you will be given the molar mass of the molecular formula.

[emily3L]

Yes, the molar mass of the molecular formula will be given. It is necessary for the calculation.

[Ruben Adamov 1E]

I’m pretty sure you need to know the molecular mass in order to find the molecular formula which is the actual number of atoms of an element in a compound. So yes it will be given.

[April Pazos 3D]

Yes, if they are asking you to find the molecular formula as well, it is necessary to provide you the molar mass for the said compound. Because the equation is the molar mass of compound/molar mass of empirical formula, we need the molar mass of the molecular formula.

[Ashrita Singh 2F]

Yes, you will have to be given the molecular mass, so you can calculate the ratio and determine the molecular formula.

[Sidharth Paparaju 3B]

Yes--we need the molar mass of the actual compound which we divide by the molar mass of the empirical formula to find the ratio. Then we multiply this ration by the empirical formula and we get the molecular formulas.

[Crystal Ma 2J]

Yes, we should be given the molar mass. In order to calculate the molecular formula, it is needed since you must find the ratio by dividing the molar mass of the compound by the molar mass of the empirical formula.

[Chem_Mod]

Hello all,

As previously noted, the molar mass is a requirement to transition from the empirical to molecular formula.

[Samantha Loc 1B]

Yes, to both questions.
In order to find the empirical formula given the sample mass and mass compositions, you would simply convert the masses to molar ratios (g to mol) by imagining the sample mass is 100g and ascribing the appropriate respective measures to each element. This would then give you the basic idea of what the ratio between elements should be for your empirical formula. Lastly, with the sample mass provided, you would be able to find the molar mass by dividing it by the molar mass of the compound and multiplying the product with the empirical formula.

[Shivani Sakthi 1l]

To directly answer your question, the molar mass of the molecular formula would be needed to be given if you are asked to find the molecular formula given mass percentages. In this step by step explanation of calculating molecular formulas, you will see why.

Step 1: Find the mass percentages of the elements within the compound. This will be given sometimes. Other times one may be given the physical amount in grams of each element within a compound. To find the mass percentage, you must add up all amounts of all the elements, giving you the total. Then divide each respective element by the total and multiple by one hundred. ex. (element A mass/ total mass) x 100 .

Step 2: Multiply each mass percentage by 100 g to get the amount of each element from a whole and unambiguous number. For example, if the mass percentage of carbon was 12.5 %, multiply by 100 g to get the amount of carbon to be 12.5 moles.

Step 3: Use the molar mass of each element to convert the amount (from 100 g) of each element to the number of moles.

Step 4: After obtaining the number of moles for each respective element, divide each value by the smallest number of moles.
For example if Carbon was 12.5 moles, Oxygen was 2.4 moles, and Nitrogen was 3.33 moles, you would divide each value by 2.4 moles.

Step 5: If your solutions are whole numbers, you have the subscripts your empirical formula. However, if they are not whole, multiply by a common factor to make each value a whole number.

STEP 6: Using your empirical formula, you can use the periodic table to calculate the empirical molar mass. However, since you do not know the molecular formula just yet, and since the empirical formula solely shows the relative ratio of atoms present in a compound, you cannot calculate the molar mass of the molecular formula. Therefore, this MUST BE GIVEN.

Step 7: divide the molar mass of the molecule by the empirical mass of the molecule to get a whole number factor. Multiply the subscripts in the empirical formula by this number to obtain the molecular formula.

[305749341]

In order to find the molecular formula, you will need to have the empirical formula and the molar mass of the molecular formula so you can multiply the ratios given. However, you can also be given the structural diagram of the molecule to get the molecular formula.

[Mugdha Dip 3d]

Hello!
I think if you are asked to find the empirical formula or the molecular formula then you should be given the molar mass.

[Rio Gagnon 1G]

Yes, the molar mass must be given in order to get from the empirical formula to the molecular formula so that you can multiply each number of moles by the ratio you get when you divide the molar mass by the mass calculated from empirical formula.

[DArcy Perlman 1C]

Yes, to calculate molecular formula you would need the molar mass from mass spectometry, which will always be given in the problem if you are asked to calculate.

[Mahika Saoji 3K]

Yes. In order to calculate, you will need the molar mass of the molecular formula. Without it, it would be very difficult to solve.