**Topic 4,**

Moles & Stoichiometry

(Key concepts)

Moles & Stoichiometry

(Key concepts)

**The concept of the mole:**

*One mole of anything = 6 x 10 23rd of those "things"

*Just as one dozen of anything = 12 of those "things"

*6 x 10 23rd is called Avogadro's number

*Used to count atoms, molecules, ions, electrons, etc.

*Two moles equals 12 x 10 23rd particles

*One-half mole equals 3 x 10 23rd particles

**Molar mass:**

*Molar mass is the mass of one mole

*Molar mass is determined by looking up the atomic mass/masses on the periodic table and using the unit gram

*Examples:

*One mole of Na has a mass of 23 g/mol

*One mole of Cl has a mass of 35 g/mol

*One mole of NaCl has a mass of 58 g/mol

*To find the mass of one mole of Ca(OH)2:

40 + 2(16) + 2(1) = 74 g/mol

**Molar volume:**

*The volume of one mole of any gas at STP occupies a volume of 22.4 liters

*2 moles of a gas at STP would occupy 44.8 L; 1/2 mole of any gas at STP would occupy 11.2 L

**Mole calculations:**

*Listed on Table T

*# moles = given mass/molar mass

*Example:

*How many moles in 29 grams of NaCl?

*Solution: The molar mass of NaCl is 58 g/mol; 29 g/58 g/mol = 0.5 mole

*% comp = mass of part/mass of whole x 100

*Example:

*What is the percent Na in NaCl? 23/58 x 100 = 40%

*water (hydration)/whole x 100

*Example:

*What is the percent hydration of

BaCl2-2H2O?

*Solution: 2H2O/BaCl2-2H2O; 2(18)/137 + 2(35) + 2(18) x 100 = 36/243 x 100 = 15%

*Must maintain the molar ratios in an equation

*Example:

*2H2 + O2 --> 2H2O

*If use 2 moles of O2, must use 4 moles of H2 and will produce 4 moles of H2O

**Percent composition by mass:**

*Listed on Table T*% comp = mass of part/mass of whole x 100

*Example:

*What is the percent Na in NaCl? 23/58 x 100 = 40%

**Percent hydration:**

*Use the percent comp formula*water (hydration)/whole x 100

*Example:

*What is the percent hydration of

BaCl2-2H2O?

*Solution: 2H2O/BaCl2-2H2O; 2(18)/137 + 2(35) + 2(18) x 100 = 36/243 x 100 = 15%

**Stoichiometry:**

*Must maintain the molar ratios in an equation

*Example:

*2H2 + O2 --> 2H2O

*If use 2 moles of O2, must use 4 moles of H2 and will produce 4 moles of H2O