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: 23.00 + 35.45– NH4OH: 14.01 + (4 x 1.008) +16.00 + 1.008

– Ca(NO3)2 40.08 + (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: 22.99– N: 14.01– O: 3 x 16.00 = 48.00– Total 85.00

• % 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 = 6.022 x 1023 of whatever you are dealing

with.– 1 mole of gold atoms = 6.022 x 1023 gold atoms– 1 mole sugar molecules = 6.022 x 1023 sugar molecules– 1 mole of poodles = 6.022 x 1023 poodles

• View a mole the same way you would a dozen:– A dozen means 12– A mole means 6.022 x 1023

• 6.022 x 1023 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 = 6.022 x 1023 carbon atoms and has a mass of 12.01 g

• 1 mole of aluminum atoms = 6.022 x 1023

Aluminum atoms and has a mass of 26.98 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 6.022• Write this answer x 1023

• Convert to scientific notation• Example 2.3 moles = ? Particles– 2.3 x 6.022 = 13.85– 13.85 x 1023

– 1.385 x 1024

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 6.022• Particles exponent – 23 = answer exponent• Convert to scientific notation• Example: 1.385 x 1024 particles is ? Moles• 1.385/ 6.022 = 0.23• 24-23 = 1• Therefore: 0.23 x 101, or 2.3 x 100, or 2.3