THE MOLE Unit 2: Quantities in Chemical Reactions SCH3U Miss Richardson THE MOLE Unit 2: Quantities in Chemical Reactions

How many are there? 52cards = 1 deck 24 bottles = 1 case 2 shoes = 1 pair 12 eggs = 1 dozen 52cards = 1 deck 24 bottles = 1 case

How many (atoms) are there? 6.022 x 1023 carbon atoms = 1 mole

Amedeo Avogadro The mass of a single atom is incredibly small. determined that any quantity of matter must contain an enormous number of atoms, ions, molecules, etc. he showed that 12.01g of carbon contains 6.02 x 1023 atoms Why is 12.01g a significant quantity?

Amedeo Avogadro Further investigations showed consistency: A sample of NaCl has an average atomic mass of 58.44 amu (22.99 + 35.45) There are 6.022 x 1023 molecules in 58.44 g of NaCl

Avogadro’s Number The quantity 6.022 x 1023 is known as Avogadro’s number (NA) and is equal to 1 mole of a substance. Eg: 1 pair of eggs = 2 eggs 1 dozen eggs = 12 eggs 1 mole of eggs = 6.022 x 1023 eggs

Counting in Chemistry monatomic elements = atoms eg: Fe(s), S(s) diatomic particles = molecules eg: O2(g), F2(g), Cl2(l) molecular compounds = molecules eg: H2O(l), SO2(g) ionic compounds = formula units eg: NaCl(s), LiOH(g)

The Mole The number of moles of a substance can be determined using this formula: Where: n = number of moles. N = number of particles NA = Avogadro’s Constant = 6.022 x 1023

Finding Number of Particles Example: An airbag contains 3.65 mol of hydrazine (N2H4(l)) How many molecules are there? N = n x NA N = 3.65 mol x 6.022 x 1023 molecules 1 mol = 2.197 300 x 1024 molecules = 2.20 x 1024 molecules

Finding Number of Particles Example: An airbag contains 3.65 mol of hydrazine (N2H4(l)) How many molecules are there? 2.20 x 1024 molecules How many atoms are there? 2.197 300 x 1024 molecules x 6 atoms 1 molecule = 1.318 38 x 1025 atoms = 1.32 x 1025 atoms

Molar Mass When testing a product, chemists need to be sure the correct number of molecules (or moles of molecules) of the active ingredient are present. To do this, we need a way to relate mass of a substance to the number of particles present. molar mass = mass of 1 mole (or 6.022 x 1023 particles) of any substance.

Calculating Molar Mass molar mass = mass of 1 mole (or 6.022 x 1023 particles) of any substance. Where: m = mass of a substance (g) n = #of moles of a substance (mol) M = molar mass (g/mol)

Molar Mass - Example What is the molar mass (M) of magnesium chloride, MgCl2? Step 1: Find atomic masses on periodic table MMg = 24.31 g/mol MCl = 35.45 g/mol Step 2: Add atomic masses, accounting for number of each atom MMgCl2 = MMg + MCl2 = 24.31 +(2x35.46) = 95.23 g/mol

Particles, Mass and Moles