Chapter 11 Mathematics & Chemical Formulas Unit 6 – The Mole

Atoms are too small/light Atoms are too small and too light to count or mass as individuals – One Carbon-12 atom = 1.99 x grams We use this as the basis for atomic mass units. 1 Carbon atom is 12 amu. – 6 protons + 6 neutrons = 12 “things” that make up the mass of a carbon atom One amu = 1/12 of a carbon atom

Atomic Mass & Formula Mass Atomic mass - the mass of 1 mole of atoms (also known as “molar mass”) Formula mass - the masses of all the atoms in an ionic compound. Ex: CaCl 2 Molecular Mass – the masses of all of the atoms in a molecular compound. Ex: CH 4

Formula Weight (FW) So, the formula weight of calcium chloride, CaCl 2, would be Ca: 1(40.1 amu) + Cl: 2(35.5 amu) amu To convert to molar mass, change amus to g/mol. 1 amu = 1 g/mol

Molecular Weight (MW) For the molecule methane, CH 4, the molecular weight would be C: 1(12.0 amu) 16.0 amu + H: 4(1.0 amu) The molar mass of methane would be 16.0 g/mol

1 mole - different physical states Moles provide a bridge from the molecular scale to the real-world scale.

Examples of Molar Mass List the molar masses of the following: – Zn – CuSO 4 – NaCl – H 2 O – Al 2 (SO 4 ) 3

The Mole – a word that means a # Other words that mean #s: One dozen = 12 One gross = 144 One score = 20 One ream = 500 One MOLE = 6.02 x

Where does Avogadro’s Number come from? A formula: M = N A m C The mass of 1 carbon-12 atom is 1.99 x g

Avogadro’s Number Avogadro’s Number x particles in 1 mole 1 mole of 12 C has a mass of 12 g.

Mole Conversions Moles tell you how many atoms you have, AND how much mass in grams you have. We use moles to convert from atoms and grams.

Mole Conversion Factors There are 4 possible conversion factors for mole conversions: – Show your work -use a conversion factor every time

Mole Diagram – Conversion Factors

Using your calculator To Enter 6.02 x into your calculator, use the EE button, so it would appear as 6.02E23. Practice with the two following examples

Examples: If you have 4.25 x atoms of Al, how many moles do you have? If you have 0.37 moles of Al, how many atoms do you have?

Mole Examples (lol) If you have 8.64g of Mg, how many moles do you have? If you have 1.23 moles of Phosphorous, how many grams do you have?

Mole Relationships One mole of: – atoms – ions – molecules contains Avogadro’s number of those particles. One mole of: – molecules or formula units contains Avogadro’s number times the number of atoms or ions of each element in the compound.