1. Empirical (or simplest) Formula What does empirical mean? Determined by experiment.

2. What is the simplest whole number ratio of C : H in benzene, C 6 H 6 ? 1 : 1 What is the simplest whole number ratio of C : H in acetylene, C 2 H 2 ? 1 : 1 The empirical, (or simplest), formula for both benzene and acetylene is C 1 H 1. Is this the actual, (or molecular), formula of each? No. Now look at these...

3. namemolecular formula empirical (simplest) formula lowest ratio of elements hydrogen peroxide H2O2H2O2 HO glucoseC 6 H 12 O 6 CH 2 O acetyleneC2H2C2H2 CH benzeneC6H6C6H6 CH anilineC6H7NC6H7NC6H7NC6H7N waterH2OH2OH2OH2O

4. Can the molecular (actual) formula of a compound be the same as its simplest (empirical) formula? Sometimes. But not always. Write an equation relating the mf of a compound to its sf. (ie. mf = ????) mf = n*(sf), where n = 1, 2, 3...

5. How to determine the simplest formula of a compound What is the sf of a cmpd that is 85.6% C and 14.4% H, by mass. (These will always be by mass.) In 100 g of the compound, how many grams of C will there be? 85.6 g C. How many grams H? 14.4 g H Now convert these masses to # moles...

6. mol C = 85.6 g C/12.01 g C·mol -1 (extra sf) mol C = 7.127 (No rounding ‘til end.) mol H = 14.4 g H/1.01 g H·mol -1 = 14.26 Now write mol : mol ratio of C : H. 7.127 mol C : 14.26 mol H Divide both by smallest # mol to get lowest ratio. 1.00 mol C : 2.00 mol H sf of cmpd is C 1 H 2... but...

7. Is this the molecular formula of the compound? No  CH 2 cannot exist. C needs to make four bonds. You can also solve sf problems using a table: simplest formula = C 1 H 2 (More data req’d to determine the actual formula—stay tuned.) Element%g/100gmm (g/mol) # molratio C85.6 12.017.1271 H14.4 1.0114.262

8. Try this one: A compound is 46.3% Li and 53.7% O by mass. Determine the sf of this cmpd. Make a table. sf = Li 2 O Does this formula make sense? Yes. Li 2 O is an ionic compound. Element%g/100gmm# molratio Li46.3 6.9416.6712 O53.7 16.003.3561

9. Homework p 270 7 – 12 (do ‘em all) p 273 31 – 40 (do a few)

10. So you think you’re so smart... Try this one. Make a table if you want. The percentage composition of a fuel is 81.7% C and 18.3% H by mass. Find the sf of the fuel. Can we round off C 1 H 2.66 ? No—we need to express 2.66 as a fraction. C 1 H 8/3 What can you multiply both subscripts by to get rid of the denominator? Multiply by 3  sf = C 3 H 8 When do we do this? Element%g/100gmm# molratio C81.7 12.016.801 H18.3 1.0118.112.66

11. When you see decimalmultiply all subscripts by XX.50 or ½2 XX.80 or 4/55 XX.75 or ¾4 XX.67 or 2/33 XX.60 or 3/55 XX.40 or 2/55 XX.33 or 1/33 XX.25 or ¼4 XX.20 or 1/55 XX.17 or 1/66

12. Try this one: An inorganic salt is composed of 17.6% Na, 39.7% Cr, 42.8% O. Find the sf. Table!!! ratio is Na 1 Cr 1 O 3.5, but we need to multiply by 2 to get sf = Na 2 Cr 2 O 7. Elementg/100gmm# molratio Na17.622.990.76551 Cr39.752.000.7631 O42.816.002.6753.50

13. Homework p 275 46, 42, 47 (in this order + more if you want)