1. Grouping! When with many items in a large set need to be counted, it is often useful to work with groups of items rather than individual items. ItemQuantityAmount GlovesPair2 Cans of pop Six-pack6 EggsDozen12 PensGross (12 dozen) 144 PaperReam500

3. Chemists use a quantity to group atoms and molecules that is much larger than a dozen or a ream - THE MOLE (mol) The mole is defined as the amount of substance that contains as many entities (atoms, molecules, or units) as exactly 12 g of Carbon. One mole of a substance contains 6.022 141 99 x 10 23 particles This number is Avogadro ’ s constant and for the purposes of this class we will just know it as 6.022 x 10 23 particles.

4. The mass on the periodic table is called the molar mass. 55.847 g of iron is one mole. One mole of iron has 6.022 x 10 23 atoms. So 55.847 g of iron has 6.022 x 10 23 atoms.

5. Mole Conversions

6. The Mole formula! Be able to rearrange it to solve for each of the variables! n = m MM Number of moles (mol) mass (g) Molar mass (g/mol)

7. Mole to Mass Example 2.001 mol KCl is how many grams? First you need the molar mass of KCl from the periodic table. 39.0983 + 35.4527 = 74.5510 g/mol The you need to do the conversion. 2.001 mol x74.5510 g=149.2 g 1 mol

8. Another Mole to Mass Example How many grams is in 0.42 mol of Mg(OH) 2 ? Molar mass of Mg(OH) 2 is 24.3050 + 2(15.9994) + 2(1.00794) = 58.3197 g/mol 0.42 mol x58.3197 g=24 g 1 mol

9. Mass to Mole Example You are given 157 g NaOH. How many moles is this? To solve this, you need the molar mass from the periodic table. 22.989768 + 15.9994 + 1.00794 = 39.9971 g/mol 157 g NaOH x 1 mol = 3.93 mol 39.9971g

10. Another Mass to Mole example How many moles are in 1526 g K 2 CO 3 ? Molar mass of K 2 CO 3 is 2(39.0983) + 12.011 + 3(15.9994) = 138.197 g/mol 1526 g x 1 mol=11.04 mol 138.197 g

11. Moles to Particles Example How many particles are in 10.8 mol FeO? The only thing you need for this conversion is Avogadro ’ s constant (6.022 x 10 23 ) 10.8 mol FeO x 6.022 x 10 23 particles 1 mol 6.50 x 10 24 particles

12. Another Mole to Particle Example How many atoms are in 17.6 mol of CaCl 2 ? Avogadro ’ s constant is 6.022 x 10 23 17.6 mol CaCl 2 x 6.022 x 10 23 atoms 1 mol 1.06 x 10 25 atoms

13. Moles to Volume at STP Example Volume at standard temperature (25 o C) and pressure (1 atm) is a constant of 22.4 L. How many L are in 25.5 mol Al 2 O 3 ? All you need to do the conversion is the constant of 22.4 L. 25.5 mol x 22.4 L =571 L 1 mol

14. Volume to Mole Example at STP How many moles in 6.85 L of Cl 2 gas? All you need is the constant. 6.85 L x 1 mol =0.306 mol 22.4 L

15. When you calculate and use the molar mass of a compound, you are making an important assumption. Say you are working with water, you are assuming that every sample of water contains two hydrogen and one oxygen and the mass ratio is 2(1.00794) to 1(15.9994).

16. At this point, now that we have the periodic table, this two-to-one ratio seems obvious. But when scientists first discovered that compounds contained elements in fixed mass proportions, they did not have the periodic table. In fact, the discovery of fixed mass proportions was an important step toward the development of atomic theory.

17. FYI There are an infinite number of significant digits in a mole, so don’t assume it to have only 1! You MUST convert ALL quantities into standard units (L, g, etc) to use in all formulas Molar masses for molecules are calculated based on their FORMULA

18. For full marks you MUST SHOW ME ALL STEPS, FORMULAS, INCLUDE FINAL STATEMENTS and correct SIGNIFICANT DIGITS My advise… carry your units through all calculations so that you can be sure your answer is correct when they cancel out properly