Unit 2: Chemical Quantities SCH 4C

The Chemist’s Dozen  How many in a couple?  How many in a few?  How many in a dozen?  How many in a ream? Just like you associate these terms with a number, the mole is too!

The Chemist’s Dozen  The mole is the chemist’s dozen  1 mole = 6.02 x particles  That is 602 sextillion  Or   This is called Avogadro’s number

Avogadro’s Number  Like a dozen, a mole is used to measure the amount of a substance.  If you have 1 dozen donuts, you have 12 donuts.  If you have 1 mole of donuts, you have 6.02 x donuts x donuts.  In chemistry, the mole is commonly used to count atoms, formula units and molecules.

The Mole and Mass  The molar mass of a substance is the mass of 6.02 x particles of that substance.  The molar mass of an element is equal to the atomic mass in g/mol.  The molar mass of a compound is equal to the sum of the atomic mass of all the elements present in g/mol.

Molar Mass  Find the molar mass of:  Fe Pt  C 12 H 22 O 11 Ca(NO 3 ) g/mol195.1 g/mol 12C + 22H + 11O 12(12.01) + 22(1.01) + 11(16.0) g/mol Ca + 3N + 9O (14.01) +9(16.0) g/mol

Relating Moles to Mass  To calculate the mass represented by a certain number of moles of a substance, we use the relationship:  Where n= moles (mol) m = mass (g) M = molar mass (g/mol) m = n M

Finding moles…  How many moles are represented by 56.2g of Cu? n = m = 56.2g M 63.5 g/mol = mol

Finding Mass…  Calculate the mass of 6.72 mol of Na 2 CO 3. M = g/mol m = n x M = (6.72 mol)( g/mol) = g

Time to Work  Pg 85 #4 and pg 99 # 9-11  Pg #1-5  Pg 100 #12, 13  Pg #14-17

The Mole and the Number of Particles  One mole of a substance is the amount of a substance containing 6.02 x particles of that substance.  1 mole of Na is 6.02 x atoms  1 mole of Cl 2 is 6.02 x molecules  1 mole of NaCl is 6.02 x formula units  1 mole of H 2 O is 6.02 x molecules 6.02 x is Avogadro’s Number and is given the symbol N A.

 To calculate the number of particles in a sample of a substance we use the relationship: The Mole and the Number of Particles N = n N A Where N is the number of particles (atoms, molecules, formula units) n is the number of moles (mol) n is the number of moles (mol) N A is Avogadro’s number (atoms/mol, molecules/mol, formula units/mol) N A is Avogadro’s number (atoms/mol, molecules/mol, formula units/mol)

Finding the Number of Particles  How many atoms are represented by 2.6 mol of Fe?

Finding the Number of Moles  How many moles are present in a sample containing 5.63 x molecules of H 2 O?

Finding the Number of Atoms in a Sample  How many atoms of hydrogen are present in a sample containing 8.63 mol of methane, CH 4 ?

Time to Work  Pg 98 #6-8  Pg 105 #18-21