AP CHEMISTRY CHAPTER 4 SOLUTION STOICHIOMETRY

1. AP CHEMISTRYCHAPTER 4SOLUTION STOICHIOMETRY

2. Electrons aren’t shared evenly (oxygen is more electronegative)Electrons spend more time close to O than to H.

3. This uneven distribution of charge makes water polar. Because of this, water is a good solvent. The positive end (H) attracts negative ions or the negative end of another polar molecule. The negative end of water (O) attracts the positive ions or the positive end of another polar molecule.

4. When water surrounds an ionic crystal, the H end attracts the anion and the O end attracts the cation. This process is called hydration.

5. Hydration causes salts (ionic compounds) to dissolve. H2O also dissolves polar covalent substances such as C2H5OH. H2O doesn’t dissolve nonpolar covalent substances because there is not enough attraction between the water and the nonpolar molecule.

6. Hydration

7. Show the association of the ions with some water molecules when 1 formula unit of KCl dissolves in excess water. Cl- K+

8. A solution is a homogeneous mixture. In a solution, a solute dissolves in the solvent. If the solute ionizes in the solution, electricity can be conducted and the solute is said to be an electrolyte. If the solute ionizes 100% or nearly 100%, it is called a strong electrolyte. Lesser ionization occurs with weak electrolytes.

9. Svante Arrhenius determined that the extent to which a solution can conduct an electrical current depends directly on the number of ions present.

10. Solubility- is usually shown as g/given volume solvent or moles/given volume solution

11. Strong electrolytes1.soluble salts2.strong acids –completely ionize HCl(aq), HNO3(aq), H2SO4(aq)

12. Ex. Show how HCl dissociates when dissolved in water. HCl  H+ + Cl-

13. Acid (Arrhenius) – a substance that produces H+ ions in water solution

14. 3.strong bases- completely ionize-contain OH-bitter taste and slippery feel-NaOH, KOH

15. Weak electrolytes -only ionize slightly (weak acids and bases) HC2H3O2 H+ + C2H3O2 99% 1%

17. Ammonia (NH3) -weak base NH3 + H2O  NH4+ + OH

18. Molarity (M) = moles of solute liters of solution Molarity is the most common unit of concentration used in Chemistry. We may also see mM (millimolar) = moles of solute mL of solution

19. Ex. Calculate the molarity of a solution made by dissolving 23.4g of sodium sulfate in enough water to form 125 mL of solution. 23.4 g Na2SO4 1 mol Na2SO4 = 0.165 mol Na2SO4 142.06g Na2SO4 0.165 mol = 1.32 M 0.125 L

20. Ex. How many grams of Na2SO4 are required to make 350 mL of 0.50 M Na2SO4? 0.350L 0.50 mol Na2SO4 142.06g Na2SO4 = 24.9g 1 L 1 mol Na2SO4

21. Ex. What volume of 1.000 M KNO3 must be diluted with water to prepare 500.0 mL of 0.250 M KNO3? Dilution problem (M1V1 = M2V2) (1.000M)(V1) = (0.250M)(500.0mL) V1 = 125 mL Remember, this formula can only be used for dilution! Never use it for a chemical reaction (stoichiometry)!

22. Read procedure for using volumetric flasks and types of pipets. We will be using both in several labs this year.

24. Let’s Review Equation Writing from Chemistry I Some reactions fit neatly into a certain “category” of reaction type, some do not.

25. DECOMPOSITION REACTIONS

26. Reaction where a compound breaks down into two or more elements or compounds. Heat, electrolysis, or a catalyst is usually necessary.

27. A compound may break down to produce two elements.Ex. Molten sodium chloride is electrolyzed. 2NaCl(l) 2Na + Cl2

28. A compound may break down to produce an element and a compound.Ex. A solution of hydrogen peroxide is decomposed catalytically.2H2O2 2H2O + O2

29. A compound may break down to produce two compounds.Ex. Solid magnesium carbonate is heated.MgCO3 MgO + CO2

30. Metallic carbonates break down to yield metallic oxides and carbon dioxide.

31. Metallic chlorates break down to yield metallic chlorides and oxygen.

32. Hydrogen peroxide decomposes into water and oxygen.

33. Sulfurous acid decomposes into water and sulfur dioxide.

34. Carbonic acid decomposes into water and carbon dioxide.

35. Hydrated salts decompose into the salt and water. Na2CO3H2O  Na2CO3 + H2O

36. ADDITION REACTIONS Also known as Synthesis, Combination, or Composition

37. Two or more elements or compounds combine to form a single product.

38. A Group IA or IIA metal may combine with a nonmetal to make a salt.

39. A piece of lithium metal is dropped into a container of nitrogen gas. 6Li + N2 2Li3N

40. Two nonmetals may combine to form a molecular compound. C + O2 →CO2

41. When an element combines with a compound, you can usually sum up all of the elements on the product side.Ex. PCl3 + Cl2 PCl5 This is a trick that works because the common positive oxidation states of P are + 3 and +5.

42. Two compounds combine to form a single product.Ex. Sulfur dioxide gas is passed over solid calcium oxide.SO2 + CaO  CaSO3

43. A metallic oxide plus carbon dioxide yields a metallic carbonate. (Carbon keeps the same oxidation state)

44. A metallic oxide plus sulfur dioxide yields a metallic sulfite. (Sulfur keeps the same oxidation state)

45. A metallic oxide plus water yields a metallic hydroxide.A nonmetallic oxide plus water yields an acid.

46. Double Replacement (metathesis)

47. Two compounds react to form two new compounds. No changes in oxidation numbers occur. All double replacement reactions must have a "driving force" that removes a pair of ions from solution.

48. Formation of a precipitate: A precipitate is an insoluble substance formed by the reaction of two aqueous substances. Two ions bond together so strongly that water can not pull them apart. You must know your solubility rules to write these net ionic equations!

49. Simple Rules for Solubility 1. Most nitrate (NO3) salts are soluble. 2. Most alkali (group 1A) salts and NH4+are soluble. 3. Most Cl, Br, and I salts are soluble(NOTAg+, Pb2+, Hg22+) 4. Most sulfate salts are soluble(NOTBaSO4, PbSO4, HgSO4, CaSO4) 5. Most OH salts are only slightly soluble(NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble) 6. Most S2, CO32, CrO42, PO43 salts are only slightly soluble.

50. SOLUBILITY SONG To the tune of “ My Favorite Things” from “The Sound of Music” Nitrates and Group One and Ammonium, These are all soluble, a rule of thumb. Then you have chlorides, they’re soluble fun, All except Silver, Lead, Mercury I. Then you have sulfates, except for these three: Barium, Calcium and Lead, you see. Worry not only few left to go still. We will do fine on this test. Yes, we will! Then you have the--- Insolubles Hydroxide, Sulfide and Carbonate and Phosphate, And all of these can be dried!