Chemistry
Elements and Compounds

# How does one determine a molecular formula from the empirical formula?

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molar mass over grams of element

The above answer is somewhat correct. In order to find the molecular formula when given the empirical formula, you must first find the molar mass of the empirical formula.

MOLAR MASS

# atoms element A x atomic mass element A (periodic table) = mass A

# atoms element B x atomic mass element B (periodic table) = mass B

... etc.

Add up all of the mass values found above and you have the molar mass.

Then, after you have found the empirical formula's molar mass, you divide the molar mass of the molecular formula by the empirical formula's molar mass (solving for n).

MOLECULAR FORMULA EQUATION: N (Empirical formula) (read as N times empirical formula) where:

N = Molar mass substance

---- Molar Mass emp. form.

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## Related Questions  In order to find molecular formula from empirical formula, one needs to know the molar mass of the molecular formula. Then you simply divide the molar mass of the molecular formula by the molar mass of the empirical formula to find out how many empirical formulae are in the molecular formula. Then you multiply the subscripts in the empirical formula by that number. molar mass of unknown/molar mass of empirial = # of empirical units in the molecular formula. Example: empirical formula is CH2O with a molar mass of 30. If the molar mass of the unknown is 180, then 180/30 = 6 and molecular formula will be C6H12O6 The density or some other information must be given that allow you to find the molar mass. Calculate the empirical formula mass. Divide molar mass by empirical formula mass. This answer is multiplied by all subscripts of the empirical formula to get the molecular formula. An empirical formula is one that shows the lowest whole number ratio of the elements present. The molecular formula shows the composition of the molecules. An example is phosphorus pentoxide, P2O5 empirical formula, P4O10 molecular formula. Find the mass of the substance and divide it by the mass of the substance defined by the empirical formula. If you get 1, then the empirical formula is also the molecular one. The empirical formula for potassium nitrate is the same as the molecular formula, KNO3, because the molecular formula shows only one atom each of potassium and nitrogen. Any molecular formula where the subscripts do not have a common factor that can divide them all. For example: CH4 (methane) is a molecular formula that is also an empirical formula because there is no number (other then one) that can divide both the 4 and the 1. Take ethane as another example. It hasn't the empirical formula which is similar to the molecular formula. Empirical formulas determine the ratio of atoms of different elements within a chemical compound and can be derived by dividing the number of each element's atoms by their greatest common factor. They do not necessarily describe the full chemical makeup of a molecule. For example, benzene has the formula C6H6 but its empirical formula is simply CH because there is one hydrogen atom for every carbon atom. Glucose has the molecular formula of C6H12O6; its empirical formula is CH2O. Because the molecular formula for water, H2O, cannot be further simplified (empirical formulas have only whole numbers) H20 is also its empirical formula. No. A molecular formula can be the same as the empirical formula, such as CH4 (methane), because the two component atoms exist in a ratio that cannot be mathematically further broken down - one carbon to four hydrogens. In this case the molecular formula (the actual number of atoms per molecule), and the empirical formula (the simplest ratio of those numbers) is identical. On the other hand, ethane, C2H6 - two carbons to 6 hydrogens - has a molecular formula of C2H6 and a empirical formula of CH3, the ratio of 2 to 6 reduced to its simplest whole number form. Sooooooooooo, the molecular formula will always be equal to or greater than the empirical formula, and the empirical formula will always be equal to or less than the molecular formula. In other words (as if that wasn't enough), the molecular formula will never be less than the empirical formula and the empirical formula will never be greater than the molecular formula, but THE TWO CAN BE EQUAL. Whew!!! Ray By first determining the approximate molecular mass of the compound in question, usually by measurements of osmotic pressure, freezing point depression, or some other colligative property that depends on the number of molecules present. The approximate molecular mass of the substance in question is then calculated from the colligative property measurements, and this value is then divided by gram molecular mass corresponding to the empirical formula. The nearest integer to the resulting quotient is then applied as a factor by which to multiply each subscript of the empirical formula to yield the molecular formula. A molecular formula specifies the exact number of atoms of each element in one molecule of a compound, but an empirical formula shows only enough of the atoms of the element with the smallest number of atoms in the compound to specify the proportions between or among each kind of atom in the compound. The subscript numbers after each atomic symbol in a molecular formula will therefore be an integral multiple of the subscript numbers in the empirical formula for the same compound. Since 1 is an integer, the molecular formula may be the same as the empirical formula, as it is for water, for example. A contrasting example is benzene, for which the molecular formula is C6H6, while the empirical formula is simply CH. Yes. One of the simples examples is the pair butane and 2-methylpropane, which have not only the same empirical but the same molecular formula, C4H10.   CH3O: When a molecular formula has a set of subscripts that can all be integrally divided by any integer other than one, division of the subscripts by the highest such integer will yield the empirical formula. Molecular formula tells you how the actual number of atoms of each element are in one molecule of a compound. The empirical formula shows this same information as a reduced ratio. For example: H2O2 is the molecular formula of hydrogen peroxide. In one molecule of hydrogen peroxide there are two atoms of hydrogen and two atoms of oxygen. This can be thought of as a 2:2 ratio of H:O. Reduced this ratio yields 1:1, and so the empirical formula is HO. Based on % composition, one can determine the moles of each element in, say, 100 grams of compound. Then, one can see the mole ratio of all the elements in the compound, and adjust them so as to obtain whole numbers in the lowest possible ratio. This is then the empirical formula. Assuming you came upon the empirical formula by chemical analysis, the molecular formula would be a multiple of (NO2)n. The vale for n (1, 2, 3 etc) would need to be established by investigation. In this case the molecular formula is N2O4. This molecule is in equilbrium with the monomer NO2. N2O4 is the more common species at low temperatures and is the form found in the solid. NO2 is paramagnetic as it has one unpaired electron. Because you've gotten at least one of them wrong. The chemical formula of maltose is a multiple of its empirical formula, because that's kind of a requirement in the definition of "empirical formula." WO2: If any element symbol in a formula has no subscript, implying a subscript of one, the formula is already empirical. If one of the atoms is already at its smallest amount. i.e. CH4 would be the same for both, while C2H8 would also have an empirical formula of CH4 though. H2O --&gt; H2O etc. If one of the atoms is already at its smallest amount. i.e. CH4 would be the same for both, C2H8 would also have an emperical formula of CH4 though. H2O --&gt; H2O etc. In an empirical formula, at least one of the element symbols must have a subscript (possibly including the implicit subscript "1" that is presumed when there is no explicit subscript) that is a prime number. The subscripts in a chemical formula must correspond to the actual number of atoms of each element present in a molecule or formula unit of the compound and therefore may be any integral multiple of the subscripts in the empirical unit. For example, the empirical formula of both acetylene (also called "ethyne") and benzene is CH, but the chemical formulas are C2H2 for acetylene and C6H6 for benzene. The empirical formula uses as subscripts the lowest whole number ratio of atoms combined in the substance. Many ionic substances do not have a molecular formula because they form a crystal lattice and not individual molecules. Molecular compounds may have both. The molecular formula shows the actual number of combined atoms in a single molecule. No. It must be a whole number. Since the empirical formula of a compound shows the proportions of the elements in the simplest whole number ratio there is going to be at least one odd number in the formula. Multiplying by 2.5 would then result in you having half an atom somewhere in the molecule, which you can't really have.

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