2. 1 Test 2 Study Guide Thursday February 26 8:00 p.m. Dobo 134

3. 2 What’s it on? End of C 3 (page 91 forward) Chapter 4 (except (4.4 – oxidation reduction pages 128-133 and titrations pages 140- 143) Chapter 5 through 5.5 ( page 174)* Calorimetry will now be on this test* * Updated Feb 17, 2004

4. 3 What should I do? Do the first problems on the practice sheet I handed out Study the practice exam on the web (skip questions 18-20)

5. 4 Top 8 Topics Empirical Formula from weight % Limiting reactants Ionic compounds in water Strong/weak acids & bases Moles Molarity Energy Enthalpy

6. 5 Empirical Formula from weight % Given mole ratio, be able to convert to whole number ratio to get empirical formula Give mass ratio – either as grams or as a percent – be able to convert to moles and then convert mole ratio to whole number ratio to get empirical formula

7. 6 Limiting Reactants Theoretical Yield % Yield = (Actual/Theoretical) x 100 How much is used, formed, left over

8. 7 Ionic Compounds In water Strong / weak electrolytes Ionic equations Metathesis reactions Ion Solubility

9. 8 Strong acids & bases Strong acids/bases are strong electrolytes Common strong acids (Table 4.2) (memorize) –HCl HBr HI HClO 3 (chloric) HClO 4 (perchloric) HNO 3 H 2 SO 4 Common strong bases – Group I metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) –Heavy Group II metal hydroxides Ca(OH) 2, Sr(OH) 2 Ba(OH) 2

10. 9 Weak acids & bases Weak acids/bases are weak electrolytes An acid or base that is not strong is weak Examples of weak acids: –HF H 3 PO 4 H 2 SO 3 HC 7 H 5 O 2 HC 2 H 3 O 2 Example of a weak base: NH 3 A molecular substance that is not an acid or base is a nonelectrolyte

11. 10 Moles Be able to interconvert mass to moles and moles to mass How many atoms in 3 g H 2 ? (1 Mole H 2 / 2 g H 2 ) (3 g H 2 ) (2 moles atoms / Mole H 2 ) = 3 moles atoms = 18 x 10 23 atoms = 1.8 x 10 24 atoms

12. 11 Molarity Interconverting molarity, moles, volume Dilution

13. 12 Energy  E = q + w

14. 13 Enthalpy Endo, exo, sign of  H Given heat for a certain mass, calculate reaction  H Given  H and mass, calculate heat

15. 14 Top 8 Topics Let’s do some examples! Empirical Formula from weight % Limiting reactants Ionic compounds in water Strong/weak acids and bases Moles Molarity Energy Enthalpy

16. 15 A compound is 76.6%C; 6.38%H; and 17.0%O. What is the empirical formula? Divide by atomic weight to get mole ratio: –76.6 / 12 = 6.38 –6.38/1 = 6.38 –17.0/16 = 1.06 Divide mole ratio by smallest number to get whole number ratio –6.38 /1.06 = 6.02 –1.06 / 1.06 = 1 Empirical formula is C 6 H 6 O

17. 16 Limiting Reactants Theoretical Yield – how much you expect based upon the amount of reactants. If one reactant is present in excess, then the other limits how much can be made and is used to determine the theoretical yield.

18. 17 2H 2 + O 2  2 H 2 O If 10 moles of oxygen and 10 moles of hydrogen…. The hydrogen limits the amount of water that can be formed Based upon 10 moles H 2, we can make 10 moles water Based upon 10 moles O 2, we can make 20 moles water. H 2 limits. Theoretical Yield = 10 moles ( 180 g) H 2 O At end of reaction, will have 5 moles O 2 left over

19. 18 Ionic Compounds In water Strong / weak electrolytes Ionic equations Metathesis reactions Ion Solubility

20. 19 Group 1A ( alkali metals) cations soluble NH 4 + soluble NO 3 - soluble CH 3 CO 2 - = C 2 H 3 O 2 - = acetate soluble Will be given a chart for other ions

21. 20 Soluble ionic compounds in water exist as free ions surrounded by water molecules. Soluble ionic compounds are strong electrolytes Strong acids or bases (HCl, H 2 SO 4 ), NaOH) are strong electrolytes Weak acids or bases (CH 3 CO 2 H, acetic acid) are weak electrolytes Molecules that do not disassociate (CO 2, sugar) are non electrolytes.

22. 21 What kind of electrolyte am I? (NH 4 ) 2 SO 4 ? Strong HF Weak C 12 H 22 O 11 (sucrose) Non NH 3 Weak

23. 22 potassium sulfate with barium nitrate 2K + (aq) + SO 4 -2 (aq) + Ba +2 (aq) + 2 NO 3 - (aq)  2K + (aq) + 2 NO 3 - (aq) +BaSO 4 (s) SO 4 -2 (aq) + Ba +2 (aq)  BaSO 4 (s)

24. 23 Molarity Interconverting molarity, moles, volume M means moles per liter = moles/L M = moles/L If you know two things, can determine the third If you have moles and volume, can determine molarity 3 moles dissolved in 0.5 L = 3moles/0.5L = 6M

25. 24 Molarity - dilution (V conc )(M conc ) = (V dil )(M dil ) If you know 3, can solve for the fourth How many mL of 3M HCl is needed to make 100mL of 1.5 M HCl? (V conc )(3M) = (100mL)(1.5M) V conc = 50 mL

26. 25  E = q + w q > 0 heat transferred from the surroundings to the system (endothermic) q < 0 heat transferred from the system to the surroundings ( exothermic) w > 0 work is done by the surroundings on the system w < 0 work is done by the system on the surroundings q > 0, w > 0  E > 0 q < 0, w < 0  E< 0

27. 26 Enthalpy Endothermic  H > 0 Exothermic  H < 0

28. 27 Given heat for a certain mass, calculate reaction  H If it takes 60 kJ to melt 180 grams of ice, what is  H for the following reaction? H 2 O(s)  H 2 O(l) (60kJ / 180g) ( 18 g/mole) = 6 kJ/mole  H = 6kJ

29. 28 Given  H and mass, calculate heat H 2 O(s)  H 2 O(l)  H = 6 kJ How much heat is needed to melt 900 grams of ice? (900g)(6 kJ/mole)(1mole/18 g) = 300 kJ