Empirical Formula

No, you can reduce it to HO Empirical Formula: Lowest whole # ratio H2O2 (hydrogen peroxide) is it an empirical Formula? No, you can reduce it to HO

H2O2 is the molecular formula Molecular formula shows the way the molecule is actually found in nature.

How do we write empirical formulas??? 1. Take the % compositions and convert the % to grams.

11.1 % H 88.9% O changes to 11.1 g H 88.9 g O

Take the % compositions and convert the % to grams. Convert grams to moles

11.1 g H x 1 mole H = 11.1 moles 1.0 g H 88.9 g O x 1 mole O = 5.5 moles 16.0 g O

Take the % compositions and convert the % to grams. Convert grams to moles Divide by the smallest # of moles

11.1 moles H / 5.5= 2 5.5 moles O / 5.5 =1

Take the % compositions and convert the % to grams. Convert grams to moles Divide by the smallest # of moles

Plug the whole #’s into the empirical formula

11.1 moles H / 5.5= 2 5.5 moles O / 5.5 =1 H2O1

Take the % compositions and convert the % to grams. Convert grams to moles Divide by the smallest # of moles Plug the whole #’s into the empirical formula If you do not have whole #’s after dividing you must multiply through to make them all whole #’s

Examples 1.5 x 2 = 3 1.3 x 3 = 4 1.25 x 4 = 5 1.75 x 4 = 7

Examples Mn1O1.5 2x (Mn1O1.5)= Mn2O3

Molecular Mass Vs. Empirical Mass

Is found experimentally Molecular Mass Is found experimentally

Is found using the molar mass from the periodic table. Empirical Mass Is found using the molar mass from the periodic table.

Molecular Mass Vs. Empirical Mass If they are the same GREAT the Molecular Formula and Empirical Formula are the same

Molecular Mass Vs. Empirical Mass If they are not the same you must divide the Molecular mass by the Empirical mass to see how many time greater it is.

Molecular mass = 78g/mol Empirical mass of CH =13g/mol Molecular Mass Vs. Empirical Mass Molecular mass = 78g/mol Empirical mass of CH =13g/mol 78/13 =6

Molecular Mass Vs. Empirical Mass Since the molecular mass is 6 times greater then the empirical mass the formula is also 6 times greater.

Molecular Mass Vs. Empirical Mass 6 x (CH) C6H6 Molecular Formula

Using the formula you have just found you can calculate % composition.

You find the % just like you would for any % % Composition You find the % just like you would for any % Individual atom mass Total mass of the compound X100%

Example: Water H2O = total mass 18.0 Mass from H= 2(1.0)=2.0 % Composition Example: Water H2O = total mass 18.0 Mass from H= 2(1.0)=2.0 % comp. = 2/18x100% % comp. = 11% H in H2O