Basics of Moles

Molar mass Molar masses, atomic weights/masses, molecular weights/masses, formula weights/masses: all mean the same Calculate by adding the atomic masses of every atom in the formula – NaCl: – NH 4 OH: (4 x 1.008) – Ca(NO 3 ) (2 x 14.01) + (6 x 16.00)

Percent composition Mass of what you are talking about divided by mass of molecule Example: percent nitrogen in sodium nitrate – Na: – N: – O: 3 x = – Total % N is (14.01/85.00) x 100 = 16.5%

Empirical formulas Lowest ratio of subscripts Note how to calculate empirical formulas – Convert % to g – Divide each by its molar mass – Divide each by smallest – Results should be whole number +/- 0.2 – If a result rounds to X.5, multiply each subscript by 2

Molecular formulas A whole number “multiple” of an empirical formula Divide given molar mass by empirical formula’s molar mass Multiply each subscript by this value.

The mole 1 mole = x of whatever you are dealing with. – 1 mole of gold atoms = x gold atoms – 1 mole sugar molecules = x sugar molecules – 1 mole of poodles = x poodles View a mole the same way you would a dozen: – A dozen means 12 – A mole means x x is called Avogadro’s number

Molar mass The molar mass is the average atomic mass, so that is the number of grams in 1 mole of whatever you are talking about. 1 mole of carbon atoms = x carbon atoms and has a mass of g 1 mole of aluminum atoms = x Aluminum atoms and has a mass of g

Converting grams to moles Grams divided by molar mass = moles

Converting moles to grams Moles times molar mass = grams

Converting moles to particles Particles may be atoms, ions, molecules, or poodles. Moles times Avogadro’s number = particles

How to make the math easy Moles x Write this answer x Convert to scientific notation Example 2.3 moles = ? Particles – 2.3 x = – x – x 10 24

Converting particles to moles Particles may be atoms, ions, molecules, or poodles. Particles divided by Avogadro’s number = moles

How to make the math easy Divide first part of particles number by Particles exponent – 23 = answer exponent Convert to scientific notation Example: x particles is ? Moles 1.385/ = = 1 Therefore: 0.23 x 10 1, or 2.3 x 10 0, or 2.3