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So l ut i ons

So l ut i ons. Solute. A solute is the dissolved substance in a solution. Salt in salt water. Sugar in soda drinks. Carbon dioxide in soda drinks. Solvent. A solvent is the dissolving medium in a solution. Water in salt water. Water in soda. “Like Dissolves Like”.

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So l ut i ons

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  1. Solutions

  2. Solute A solute is the dissolved substance in a solution. Saltin salt water Sugarin soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Waterin salt water Waterin soda

  3. “Like Dissolves Like” Nonpolar solutesdissolve best in nonpolar solvents Polar and ionic solutesdissolve best in polar solvents

  4. Solubility Trends • The solubility of MOST solids increases with temperature. • The rate at which solids dissolve increases with increasing surface area of the solid. • The solubility of gases decreases with increases in temperature. • The solubility of gases increases with the pressure above the solution.

  5. Therefore… Solids tend to dissolve best when: • Heated • Stirred • Ground into small particles Gases tend to dissolve best when: • The solution is cold • Pressure is high

  6. Solubility Chart

  7. Saturation of Solutions • A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. • A solution that contains less solute than a saturated solution under existing conditions is unsaturated. • A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

  8. Definition of Electrolytes and Nonelectrolytes An electrolyte is: • A substance whose aqueous solution conducts an electric current. A nonelectrolyte is: • A substance whose aqueous solution does not conduct an electric current.

  9. Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

  10. Try to classify the following substances as electrolytes or nonelectrolytes… • Pure water • Tap water • Sugar solution • Sodium chloride solution • Hydrochloric acid solution • Lactic acid solution • Ethyl alcohol solution • Pure sodium chloride

  11. Answers to Electrolytes NONELECTROLYTES: ELECTROLYTES: • Pure water • Sugar solution • Ethanol solution • Pure NaCl • Tap water (weak) • NaCl solution • HCl solution • Lactate solution (weak)

  12. Ionic Compounds “Dissociate” NaCl(s)  Na+(aq) + Cl-(aq) AgNO3(s)  Ag+(aq) + NO3-(aq) MgCl2(s)  Mg2+(aq) + 2 Cl-(aq) Na2SO4(s)  2 Na+(aq) + SO42-(aq) AlCl3(s)  Al3+(aq) + 3 Cl-(aq)

  13. Ions tend to stay in solution where they canconduct a current rather than re-forming a solid. The reason for this is the polar nature of the water molecule… Positive ions associate with the negative end of the water dipole (oxygen). Negative ions associate with the positive end of the water dipole (hydrogen).

  14. Some covalent compounds IONIZE in solution Covalent acids form ions in solution, with the help of the water molecules. For instance, hydrogen chloride molecules, which are polar, give up their hydrogens to water, forming chloride ions (Cl-) and hydronium ions (H3O+).

  15. Strong acids such as HCl are completelyionized in solution. Other examples of strong acids include: • Sulfuric acid, H2SO4 • Nitric acid, HNO3 • Hydriodic acid, HI • Hydrobromic acid, HBr • Perchloric acid, HClO4

  16. Weak acids such as lactic acid usually ionize less than 5% of the time. Many of these weaker acids are “organic” acids that contain a “carboxyl” group. The carboxyl group does not easily give up its hydrogen.

  17. Because of the carboxyl group, organic acids are sometimes called “carboxylic acids”. Other organic acids and their sources include: • Citric acid – citrus fruit • Malic acid – apples • Butyric acid – rancid butter • Amino acids – protein • Nucleic acids – DNA and RNA • Ascorbic acid – Vitamin C This is an enormous group of compounds; these are only a few examples.

  18. Solution Concentration

  19. Calculations of Solution Concentration:Mass Percent Mass percentis the ratio of mass units of solute to mass units of solution, expressed as a percent

  20. A Simplifying Assumption • 1 ml of water = 1 gram of water • 1000 ml of water = 1 liter = 1000 grams • Assume that solutions with water as the solvent have the density of pure water (1 mL = 1 gram) • It’s not true, but it’s close enough 

  21. Calculations of Solution Concentration Mole fraction – the ratio of moles of solute to total moles of solution

  22. Calculations of Solution Concentration:Molarity Molarity is the ratio of moles of solute to liters of solution

  23. Preparation of Molar Solutions Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution? • Step #1: Ask “How Much?” (What volume to prepare?) • Step #2: Ask “How Strong?” (What molarity?) • Step #3: Ask “What does it weigh?” (Molar mass is?) 1.500 L 0.500 mol 58.44 g = 43.8 g 1 L 1 mol

  24. Calculations of Solution Concentration Molality – moles of solute per kilogram of solvent

  25. Serial Dilution Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution? MstockVstock = MdiluteVdilute (11.6 M)(x Liters) = (3.0 M)(0.250 Liters) x Liters = (3.0 M)(0.250 Liters) 11.6 M = 0.065 L

  26. Precipitation Reactions Graphic: Wikimedia Commons User Tubifex

  27. Double Replacement Reactions The ions of two compounds exchange places in an aqueous solution to form two new compounds. AX + BY  AY + BX One of the compounds formed is usually a precipitate (an insoluble solid), an insoluble gas that bubbles out of solution, or a molecular compound, usually water.

  28. Double replacement forming a precipitate… Lead(II) nitrate + potassium iodide  lead(II) iodide + potassium nitrate Double replacement (ionic) equation Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq) Complete ionic equation shows compounds as aqueous ions Pb2+(aq) + 2 NO3-(aq) + 2 K+(aq) +2 I-(aq)  PbI2(s) + 2K+(aq) + 2 NO3-(aq) Net ionic equation eliminates the spectator ions Pb2+(aq) + 2 I-(aq)  PbI2(s)

  29. Solubility Rules – Mostly Soluble

  30. Solubility Rules – Mostly Insoluble

  31. Solubility Chart:Common saltsat 25C S = Soluble I = Insoluble P = Partially Soluble X = Other

  32. ACIDS AND BASES www.lab-initio.com

  33. Properties of Acids • Acids are proton (hydrogen ion, H+) donors • Acids have a pH lower than 7 • Acids taste sour • Acids effect indicators • Blue litmus turns red • Methyl orange turns red • Acids react with active metals, producing H2 • Acids react with carbonates • Acids neutralize bases

  34. Acids are Proton (H+ ion) Donors Strong acids are assumed to be 100% ionized in solution (good H+donors). HCl H2SO4 HNO3 Weak acids are usually less than 5% ionized in solution (poor H+donors). H3PO4 HC2H3O2 Organic acids

  35. Acids Have a pH less than 7

  36. Acids Effect Indicators Bluelitmus paper turnsredin contact with an acid. Methyl orange turnsredwith addition of an acid

  37. Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas. Mg + 2HCl  MgCl2 + H2(g) Zn + 2HCl  ZnCl2 + H2(g) Mg + H2SO4 MgSO4 + H2(g)

  38. AcidsReact withCarbonates 2HC2H3O2+Na2CO3 2 NaC2H3O2 + H2O + CO2

  39. Effects of Acid Rain on Marble(calcium carbonate) George Washington: BEFORE George Washington: AFTER

  40. Acids Neutralize Bases Neutralization reactions ALWAYSproduce a saltandwater. HCl + NaOH NaCl+H2O H2SO4 + 2NaOH  Na2SO4+2H2O 2HNO3 + Mg(OH)2 Mg(NO3)2+2H2O

  41. Properties of Bases • Bases are proton (hydrogen ion, H+) acceptors • Bases have a pH greater than 7 • Bases taste bitter • Bases effect indicators • Red litmus turns blue • Phenolphthalein turns purple • Solutions of bases feel slippery • Bases neutralize acids

  42. Bases are Proton (H+ ion) Acceptors • Sodium hydroxide (lye), NaOH • Potassium hydroxide, KOH • Magnesium hydroxide, Mg(OH)2 • Calcium hydroxide (lime), Ca(OH)2 OH-(hydroxide) in base combines with H+in acids to form water H+ + OH- H2O

  43. Bases have a pH greater than 7

  44. Bases Effect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns bright pinkin a base.

  45. Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH)2 MgCl2 + 2 H2O

  46. Oxidation-Reduction Reactions“Redox” LEO SAYS GER

  47. Oxidation and Reduction (Redox) • Electrons are transferred • Spontaneous redoxrxns can transfer energy • Electrons (electricity) • Heat • Non-spontaneous redoxrxns can be made to happen with electricity

  48. Oxidation Reduction Reactions(Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:

  49. LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

  50. Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are not redoxrxns. Examples:

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