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what is simple formula and molecular formula?

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A "simple" formula, more commonly known as the empirical formula, and a molecular formula are both ways of expressing the components of a compound using the accepted abbreviations.  In the empirical formula, the number of atoms is unaccounted for as only the elemental components are shown and one empirical formula may represent multiple compounds.  In the molecular formula, all atoms are accounted for and it is specific to that compound.  For example, hydrogen peroxide (H2O2) has 4 atoms.  In the empirical formula, these 4 atoms would not be accounted for and it would simply be written as HO, because there is a 2:2 ratio, which is the same as a 1:1 ratio.  In the molecular formula, all atoms would be accounted for and it would be written H2O2.  An example where the empirical formula is the same would be glucose (C6H12O6), ribose (C5H10O5), and formaldehyde (CH2O).  The molecular formula for each of these is unique, as you can see in the parentheses.  However, the empirical formula for all of these is CHO.

I hope this helps you!!!!

I've never heard the expression "simple formula" used before but I presume you are talking about the difference between the empirical formula and the molecular formula. The empirical formula of a compound is the one with the lowest molar ratio of each atom in the molecule.

As an example, most carbohydrates have the empirical formula of CH2O. All molecular formulas have a single factor multiplied by the ratios of 1:2:1 for C:H:O.

Ribose is a 5 carbon sugar and has a molecular formula of 5*(CH2O) = C5H10O5.

Glucose is a 6 carbon sugar and has a molecular formula of  6*(CH2O) = C6H12O6.

Comments

To clarify, simple sugars have the empirical formula of CH2O.

polysaccharides (e.g., sucrose, starch) are formed by linking simple sugars together, but H2O is lost each time that happens (sucrose is composed of two simple sugars, with a link between them, so there is one H2O less than expected)

To further clarify this clarification, starch is a polymer of glucose and has a variable molecular formula that is an integer multiple of its empirical formula: (C6H10O5)n. Where n is the number of glucose molecules that have been incorporated into the polymer. There are examples of other monosaccharides or "simple sugars" like deoxyribose and fucose that do not follow the CH2O empirical formula as well. My intention was not to get involved in a lengthy discussion of sugars but only to use two examples to illustrate a point about your question regarding empirical and molecular formulas.