1. CHEMISTRY TUESDAY, 1/26 As you come in, take out a blank piece of paper and something to write with.

2. MOLE CONVERSIONS (REVIEW) How many moles is 2.80*10 24 atoms of silicon?

3. MOLE CONVERSIONS (REVIEW) ANSWER: 4.65 moles Si

4. MOLE CONVERSIONS (REVIEW) Find the mass, in grams, of 4.52*10 -3 moles of eicosane, C 20 H 42.

5. MOLE CONVERSIONS (REVIEW) ANSWER: 1.27 g C 20 H 42

6. MOLE CONVERSIONS (REVIEW) Find the number of atoms in 3.70*10 -1 grams of boron.

7. MOLE CONVERSIONS (REVIEW) ANSWER: 2.06*10 22 atoms B

8. 1 horse = 500 pounds 1 cow = 400 pounds 1 pig = 90 pounds 1 donkey = 80 pounds 1 sheep = 60 pounds 1 bird = 5 pounds What percent of the total mass is the donkey? QUICK PRACTICE ON SCRATCH PAPER

9. THE PERCENT COMPOSITION OF A COMPOUND The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%.

10. EMPIRICAL FORMULAS What does the empirical formula of a compound show?  The empirical formula gives the lowest whole-number ratio of the atoms of the elements in a compound. 10.3

11. EMPIRICAL FORMULAS  Ethyne (C 2 H 2 ) is a gas used in welder’s torches. Styrene (C 8 H 8 ) is used in making polystyrene.  These two compounds of carbon have the same empirical formula (CH) but different molecular formulas. 10.3

12. EMPIRICAL FORMULAS PRACTICE #1 together #2 with partner

13. MOLECULAR FORMULAS How does the molecular formula of a compound compare with the empirical formula? The molecular formula of a compound is either the same as its experimentally determined empirical formula, or it is a simple whole-number multiple of its empirical formula. 10.3

14. MOLECULAR FORMULAS 10.3

15. MOLECULAR FORMULAS PRACTICE #1 together #2 with partner

16. HOMEWORK Mole conversions U5WS2