1. The Mole Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?

2. Background: Atomic Masses Look at the “atomic masses” on the periodic table. What do these represent? –E.g. the atomic mass of C is 12 (atomic # is 6) We know there are 6 protons and 6 neutrons Protons and neutrons have roughly the same mass. So, C weighs about 12 u (atomic mass units). –TB: why is the atomic mass not exactly 12 on the periodic table? What is the actual mass of a C atom? –Answer: approx. 2 x 10 -23 grams (protons and neutrons each weigh about 1.7 x10 -24 grams) Two problems: 1.Atomic masses do not convert easily to grams 2.They can’t be weighed (they are too small)

3. The Mole With these problems, why use atomic mass at all? - Atomic masses give information about # of p +, n 0, e – It has been found that 1 g H, 12 g C, or 23 g Na have 6.02 x 10 23 atoms 6.02 x 10 23 = a “mole” or “Avogadro’s number” “mol” is used in equations, “mole” is used in writing; –one gram = 1 g, one mole = 1 mol. Unit used to measure the amount of molecules/individual particles in a substance

4. Mollionaire! Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second? A: $ 6.02 x 10 23 / $1 000 000 000 = 6.02 x 10 14 payments = 6.02 x 10 14 seconds 6.02 x 10 14 seconds / 60 = 1.003 x 10 13 minutes 1.003 x 10 13 minutes / 60 = 1.672 x 10 11 hours 1.672 x 10 11 hours / 24 = 6.968 x 10 9 days 6.968 x 10 9 days / 365.25 = 1.908 x 10 7 years A: It would take 19 million years

5. Comparing sugar (C 12 H 22 O 11 ) & H 2 O No, sugar has more (45:3 ratio) Yes (6.02 x 10 23 in each) Yes. No, molecules have dif. masses No, molecules have dif. sizes. 1 mol each Yes, that’s what grams are. mass? No, they have dif. molar masses # of moles? No, they have dif. molar masses # of molecules? No # of atoms? No, they have dif. densities. volume? 1 gram eachSame

6. Molar mass The mass of one mole is called “molar mass” E.g. 1 mol Li = 6.94 g Li This is expressed as 6.94 g/mol What are the following molar masses? SSO 2 Cu 3 (BO 3 ) 2 32.06 g/mol 64.06 g/mol 308.27 g/mol Calculate molar masses (to 2 decimal places) CaCl 2 (NH 4 ) 2 CO 3 O 2 Pb 3 (PO 4 ) 2 C 6 H 12 O 6 Cux 3 = 63.55 x 3= 190.65 Bx 2 = 10.81 x 2= 21.62 Ox 6 = 16.00 x 6= 96.00 308.27

7. Molar mass The mass of one mole is called “molar mass” E.g. 1 mol Li = 6.94 g Li This is expressed as 6.94 g/mol What are the following molar masses? SSO 2 Cu 3 (BO 3 ) 2 32.06 g/mol64.06 g/mol 308.27 g/mol Calculate molar masses (to 2 decimal places) CaCl 2 (NH 4 ) 2 CO 3 O 2 Pb 3 (PO 4 ) 2 C 6 H 12 O 6 110.98 g/mol (Ca x 1, Cl x 2) 96.11 g/mol (N x 2, H x 8, C x 1, O x 3) 32.00 g/mol (O x 2) 811.54 g/mol (Pb x 3, P x 2, O x 8) 180.18 g/mol (C x 6, H x 12, O x 6)

8. Converting between grams and moles If we are given the # of grams of a compound we can determine the # of moles, & vise-versa In order to convert from one to the other you must first calculate molar mass m = n x M n = m  M This can be represented in an “ equation triangle ” m nM m= n x M0.25HCl 53.15H 2 SO 4 3.55NaCl 1.27Cu Equation n (mol) m (g) M (g/mol) Formula 9.136.46 n= m  M 0.541998.08 m= n x M20758.44 n= m  M 0.020063.55

9. Converting between grams and number of particles (atoms, molecules, compounds, etc.) Once you know the amount of a substance (n), you can then calculate the number of particles (N) by going back to our first equation triangle that includes Avagadro’s number (N A ) N nNANA

10. Determine the number of molecules of water in an ice cube of mass 12.6 g. 1 st – convert m  n 2 nd – convert n  N A little more tricky Calculate the number of atoms in 1.00 g of nitrogen. Calculate the number of chloride ions in 22.2 g of CaCl 2 N nNANA m nM

11. Homework! Pg. 226 #2,3 Pg. 228, 230, 231 – odd numbers Pg. 235 #31,33 Pg. 237, 239, 242 – odd numbers