Chemistry
Elements and Compounds

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

012 ###### 2013-04-17 17:51:13

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.

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## Related Questions  According to biologists, the reason an empirical formula is not double that of the monosaccharide is because it loses one water molecule. 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. 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. A formula unit includes the correct number of each kind of atoms present in a molecule of a covalently bonded compound, but an empirical formula does not necessarily do so. An empirical formula is reliable with respect to the ratios between each kind of atom, but the molecule may contain any positive integral number of empirical formulas, including one. The proportions of elements that combine to form one molecule. 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 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. 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. 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. the empirical formula is the simplest whole number ratio of the elements present in one molecule or formula unit of a compounds we calculate the empirical formula using the following steps: 1. note the mass of each element correctly 2. divide the atomic masses by the masses deduced in step 1 3. divide the step 2 calculation by the lowest figure 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. 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. 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 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. If the replacement group has the empirical formula CnH(2n +1), the product is an alcohol. 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. 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. The empirical formula gives the simplest ratio of the elements in a compound, but does not necessarily give the actual number of each element. For instance the empirical formula of water is H2O - two hydrogens for each oxygen - and each molecule does actually contain two hydrogen atoms and one oxygen atom. But in the case of glucose, the empirical formula is CH2O - two hydrogens for each carbon and oxygen - but the molecule actually contains six carbons, twelve hydrogens and six oxygens. Yes, it LOOKS like an empirical formula BUT it is NOT a correct one:Either C9H20 or C8H18 are correct (both are saturated alkanes) but not C8H20 For example, all linear alkenes with one double bond and no other functional groups have the same empirical formula. molar mass over grams of elementThe 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. The empirical formula for carbon dioxide is CO2 (that 2 is supposed to be small...). So, there are two atoms of oxygen in one carbon dioxide molecule (there is also a clue in the name: "di" can sometimes mean 2). 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.

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