An Introduction…..

1. Stoichiometry An Introduction…..

2. Background: Atomic masses • Atomic Mass: Where can you find it? • An atomic mass unit is defined as 1/12 the weight of the carbon-12 isotope. The old symbol was amu, while the most correct symbol is u (a lower case letter u). • The atomic mass of any element is the “average” atomic mass and found on the periodic table.

3. Background: Atomic masses Two problems with atomic mass • Atomic masses do not convert easily to grams • They can’t be weighed (they are too small) Therefore, atomic mass is not that practical! And we need something that is……..

4. The Mole No, not a little critter but a number………

5. The Mole • A counting unit! • Similar to a dozen, except instead of 12, it’s 602,000,000,000,000,000,000,000 • 6.02 X 1023 (in scientific notation) often called Avogadro’s # • This number is named in honor of Amedeo Avogadro (1776 – 1856)

6. Here is how the International Union of Pure and Applied Chemistry (IUPAC) defines "mole:" • The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

7. What is Avogadro's Number again? one mole of ANYTHING contains 6.02 x 1023 entities. In other words, there are 6.02 x 1023 anythings in one mole of anything!

8. Molar Mass • The mass of one mole is called “molar mass” • The unit is g/mol • Equal to the numerical value from periodic table, or add the mass of the atoms together for a molecule 1 mole of C atoms = 12.0 g/mol 1 mole of Mg atoms = 24.3 g/mol 1 mole of O2 molecules = 32.0 g/mol

9. Molar Mass of Compounds • The molar mass (MM) of a compound is determined the same way, except you add up all the atomic masses for the molecule

10. Molar Mass of Compounds Don’t forget the subscripts!!!! Ex. Molar mass of CaCl2 • Avg. Atomic mass of Calcium = 40.08g • Avg. Atomic mass of Chlorine = 35.45g • Molar Mass of calcium chloride = 40.08 g/mol Ca + (2 X 35.45) g/mol Cl 110.98 g/mol CaCl2 20 Ca40.08 17Cl 35.45

11. Flowchart Particles (Atoms or Molecules) Divide by 6.02 X 1023 Multiply by 6.02 X 1023 Moles Multiply by atomic/molar mass from periodic table Divide by atomic/molar mass from periodic table Mass (grams)

12. Calculations molar mass Avogadro’s numberGrams Moles particles Everything must go through Moles!!!

13. Try it together: • What is the molar mass (MM) of: lead (II) nitrate Pb(NO3)2 Pb 207.2 g/mol N  14.0 g/mol x 2 O  15.99 g/mol x 6 207.2 + (14.0 x 2) + (15.99 x 6) = 331.14 g/mol

14. Finding MM Practise: • Find the molar mass of the following: • PbSO4 • Ca(OH)2 • Na3PO4 • (NH4)2CO3 • C6H12O6 • Fe3(PO4)2 • Zn(C2H3O2)2 • Complete page 57 #16, 17, 18, 19

15. Day 2

16. Mass to Moles How many moles of KBr are in a 34.91 g sample? Find MM: 39.09 +79.9 = 118.9 g/mol KBr x mol = 34.91 g x ___1 mol = 0.29 mol KBr 118.9 g

17. Moles to Mass How many grams of CaCl2 are in a 0.450 mol sample? Find MM: 40.07 +(35.4 x2) = 110.87g/mol CaCl2 x g = 0.450 mol x 110.87 g = 49.89 g CaCl2 1 mol

18. Mass to particles Magnesium and oxygen react to form MgO ,how many molecules of MgO are contained in a 12.56g sample of MgO ? Find MM: 24.3 +15.99 = 40.29 g/mol MgO x molecules = 12.56 g x 1 mol 40.29 g x 6.02 x 1023 molecules 1 mol = 1.88 x 1023 molecules of MgO

19. Need to get atoms? • Set up a conversion with atoms per molecule Ex: (NH4)2S How many individual atoms are there in this molecule? 2 + 8 + 1 = 11 atoms for 1 molecule

20. Mass to atoms Magnesium and oxygen react to form MgO ,how many atoms of MgO are contained in a 12.56g sample of MgO ? Find MM: 24.3 +15.99 = 40.29 g/mol MgO x molecules = 12.56 g x 1 mol 40.29 g x 2 atoms 1 molecule x 6.02 x 1023 molecules 1 mol = 3.75 x 1023 atoms of MgO

21. Try it: • Pg 59 # 20 • Pg 60 # 24 • Pg 63 # 28 (formula units = molecules) • Pg 64 # 34