1. Mass, Moles, and Molar Mass Read pp. 80-105 (2.1 and 22) Extension Questions p. 92 #1, 4, 8-10 p. 106 #1-10

2. Atomic Mass Atomic Mass – the mass of one atom of an element (unit: u) Ex. Carbon is 12.01 u; Hydrogen is 1.01 u

3. The Mole A mole is 6.02 x 10 23 entities (atoms or molecules) of something (element or compound). The number 6.02 x 10 23 is known as Avogadro’s constant (N A ). 6.02 x 10 23 carbon atoms weigh a total of 12.01 g. 1 mol of magnesium atoms (6.02 x 10 23 ) weighs 24.3 g. Notice something????

4. Molar Mass Molar Mass – the mass of one mole of a chemical entity (unit: g/mol) M = m n Remember to use a capital M for molar mass and a lower- case m for mass!

5. Molar Mass What is the molar mass for: a)NaClb) CaCl 2 M = 22.99 g/mol + 35.45 g/mol M = 40.08 g/mol + 2(35.45 g/mol) = 58.44 g/mol = 110.98 g/mol

6. Performing calculations… m = mass (unit: g) n = mole (unit: mol) M = molar mass (unit: g/mol)

7. Example 1 How many grams of NaHCO 3 are in 0.673 moles? m = n x M = 0.673 mol x 84.01 g/mol = 56.54 g

8. Example 2 How many moles of KMnO 4 are there if you have 250 g of it? n = m / M = 250 g / 158.04 g/mol = 1.58 mol

9. Example 3 Calculate the molar mass of an element, if 2.220 mol has a mass of 26.66 g. Identify the element. M = m / n = 26.66 g / 2.220 mol = 12.01 g/mol Element is Carbon

10. Counting the number of atoms from mass How many atoms of silver are in a 185.3 g lump of pure silver? Two steps: 1. Calculate amount of X (find mol) 2. Calculate # of X atoms (find N X )

11. Counting the number of atoms from mass 1. Calculate amount of Ag (find mol) n Ag = m / M = 185.3 g / 107.87 g/mol = 1.72 mol 2. Calculate # of Ag atoms (find N Ag ) # of Ag atoms = 1.72 mol x 6.02 x 10 23 atoms 1 mol = 1.04 x 10 24 atoms

12. Example 4 Count the number of nickel (Ni) atoms there are in one 5-cent coin, which weighs 5.0 grams. n Ni = m / M = 5.0 g / 58.69 g/mol = 0.085 mol # of Ni atoms = 0.085 mol x 6.02 x 10 23 atoms 1 mol = 5.12 x 10 22 atoms

13. Calculating the number of atoms in a compound Sand’s formula is SiO 2 (s). How many oxygen atoms are in a bag of pure sand, which contains 1000 g of SiO 2 ? We know: m SiO2 = 1000 g M SiO2 = 60.09 g/mol 2 atoms O = 1 unit SiO 2 1 mol SiO 2 = 6.02 x 10 23 units

14. We want N O (# of oxygen atoms) N O = n SiO2 x 6.02 x 10 23 units SiO 2 x 2 atoms O 1 mol SiO 2 1 unit SiO 2 N O = 1000 g x 6.02 x 10 23 units SiO 2 x 2 atoms O 60.09 g/mol 1 mol SiO 2 1 unit SiO 2 N O = 2.00 x 10 25 atoms Note: Same principle as finding # of atoms for an element, but in this, you are adding in the # of atoms of the element in 1 unit of the compound (eg. always 2 O atoms in 1 unit of SiO 2 ).

15. Example 5 How many atoms of nitrogen are there in 1.26 kg of nitrogen gas? n N2 = m / M = 1260 g / 28.02 g/mol = 44.97 mol # of N atoms = 44.97mol x 6.02 x 10 23 molecules N 2 x 2 atoms N 1 mol 1 molecule N 2 = 5.41 x 10 25 atoms