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Chapter 13


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Chapter 13

  1. 1. Chapter 13 Solutions
  2. 2. What is the solution? <ul><li>A solution is just a Homogeneous Mixture! </li></ul><ul><li>One material (solute) is completely dissolved in another (solvent) </li></ul>
  3. 3. How do Solutions Work? <ul><li>Compounds are either polar or non-polar. </li></ul><ul><li>A polar solvent only will dissolve a polar solute. </li></ul><ul><li>A non-polar solvent will only dissolve a non-polar solute </li></ul><ul><li>“ Like dissolves like” </li></ul>
  4. 4. Why “Like dissolves like”? <ul><li>Polar compounds will hang tightly to their own kind (like magnets). </li></ul><ul><li>They will not surround (as a solvent) or allow themselves to be surrounded (as a solute) by non-polar compounds </li></ul>
  5. 5. Concentrate on the Solution <ul><li>Concentration is a measure of how much solute is present in the solution. </li></ul><ul><ul><li>Qualitative: Described without numbers </li></ul></ul><ul><ul><li>Quantitative: Described WITH numbers. </li></ul></ul>
  6. 6. Qualitative Concentrations <ul><li>Unsaturated: The solvent can still dissolve more solute. </li></ul><ul><li>Saturated: The solution contains the maximum amount of solute. </li></ul><ul><li>Supersaturated : The solution has dissolved more than the normal maximum amount of solute </li></ul><ul><ul><li>VERY unstable! </li></ul></ul>
  7. 7. Chapter 13 Separating Mixtures
  8. 8. Separating Mixtures <ul><li>Mixtures are separated based on their physical properties. </li></ul><ul><li>Mixtures may be separated by decanting, pouring off the liquid, with a centrifuge, filtering, or evaporation </li></ul>
  9. 9. Mixtures <ul><li>If the boiling points of the components are different , distillation can separate them based on their boiling points. </li></ul><ul><li>As one component reaches its boiling point, it evaporates from the mixture and is allowed to cool and condense. This is called a distillate. </li></ul><ul><ul><li>This process continues until all the desired components have been separated from the mixture. </li></ul></ul>
  10. 10. Chapter 13 Concentration and Molarity
  11. 11. Concentration <ul><li>In a solution, the solute is distributed evenly throughout the solvent. This means that any part of a solution has the same ratio of solute to solvent as any other part of the solution. </li></ul><ul><ul><li>This ratio is the concentration of the solution. </li></ul></ul><ul><ul><li>The concentration is the amount of a particular substance in a given quantity of a solution </li></ul></ul>
  12. 13. Chapter 13 Physical Properties of Solutions
  13. 14. Electrical Conductivity <ul><li>Some substances conduct electricity and some cannot. </li></ul><ul><li>The conductivity of a substance is described as its ability to conduct an electric current. </li></ul><ul><li>The conductivity of a substance depends on whether it contains charged particles, and these particles must be able to move. </li></ul>
  14. 15. Electrical Conductivity <ul><li>Electrons move freely within a metal, thus allowing it to conduct electricity. </li></ul><ul><li>An aqueous solution of ionic compounds such as NaCl contains charged ions, which can move about. Solutions of ionic compounds conduct electricity. </li></ul><ul><li>Pure water does not conduct electricity. </li></ul>
  15. 16. Electrical Conductivity <ul><li>An electrolyte is a substance that dissolves in a liquid solvent and provides ions that conduct electricity. </li></ul><ul><li>Strong electrolytes completely dissociate into ions and conduct electricity well. </li></ul><ul><li>Weak electrolytes provide few ions in solution. </li></ul><ul><li>Covalent compounds may be strong electrolytes, weak electrolytes, or nonconductors. </li></ul>
  16. 18. Electrical Conductivity <ul><li>The extent to which electrolytes dissociate into ions is indicated by the conductivity of their solutions. </li></ul><ul><li>The sugar sucrose does not ionize at all in solution. </li></ul><ul><ul><li>It is a nonelectrolyte and does not conduct electricity. </li></ul></ul><ul><li>A nonelectrolyte is a liquid or solid substance that does not allow the flow of an electric current, either in solution or in its pure state, such as water or sucrose. </li></ul>
  17. 20. Colligative Properties <ul><li>The physical properties of water are changed when substances dissolve in it. </li></ul><ul><li>Salt can be added to icy sidewalks to melt the ice. </li></ul><ul><ul><li>The salt actually lowers the freezing point of water. </li></ul></ul><ul><ul><li>Ice is able to melt at a lower temperature than it normally would. </li></ul></ul><ul><li>This change is called freezing-point depression. </li></ul>
  18. 22. Colligative Properties <ul><li>Nonvolatile solutes such as salt also increase the boiling point of a solvent. </li></ul><ul><li>This change is called boiling-point elevation. </li></ul><ul><ul><li>For example, glycol in a car’s radiator increases the boiling point of water in the radiator, which prevents overheating. </li></ul></ul><ul><ul><li>It also lowers the freezing point, preventing freezing in cold weather. </li></ul></ul>
  19. 24. Colligative Properties <ul><li>Any physical effect of the solute on the solvent is a colligative property. </li></ul><ul><li>A colligative property is a property of a substance or system that is determined by the number of particles present in the system but independent of the properties of the particles themselves. </li></ul>
  20. 25. Colligative Properties <ul><li>Any solute, whether an electrolyte or a nonelectrolyte, contributes to the colligative properties of the solvent. </li></ul><ul><li>The degree of the effect depends on the concentration of solute particles (either molecules or ions) in a certain mass of solvent. </li></ul><ul><ul><li>The greater the particle concentration is, the greater the boiling-point elevation or the freezing-point depression is. </li></ul></ul>
  21. 27. Chapter 14 Reversible Reactions and Equilibriums
  22. 28. Complete Reactions <ul><li>If enough oxygen gas is provided for the following reaction, almost all of the sulfur will react: </li></ul><ul><li>S 8 + 8O 2 -> 8SO 2 </li></ul><ul><li>Reactions such as this one, in which almost all of the reactants react, are called completion reactions. </li></ul><ul><li>In other reactions, called reversible reactions , the products can re-form reactants. </li></ul>
  23. 29. Reversible Reactions Solid calcium sulfate, the product, can break down to make calcium ions and sulfate ions in a reaction that is the reverse of the previous one.
  24. 30. Reversible Reactions <ul><li>The reactions occur at the same rate after the initial mixing of CaCl 2 and Na 2 SO 4 . </li></ul><ul><li>The amounts of the products and reactants do not change. </li></ul><ul><li>Chemical equilibrium is a state of balance. the rate of a forward reaction equals the rate of the reverse reaction. </li></ul>
  25. 33. Equilibrium <ul><li>In equilibrium, an atom may change from being part of the products to part of the reactants many times. </li></ul><ul><li>But the overall concentrations of products and reactants stay the same. </li></ul><ul><li>For chemical equilibrium to be maintained, the rates of the forward and reverse reactions must be equal. </li></ul>
  26. 34. Chapter 14 Systems and Stress
  27. 35. STRESS
  28. 36. Le Chatelier’s Principle <ul><li>Stress is another word for something that causes a change in a system at equilibrium. </li></ul><ul><li>Chemical equilibrium can be disturbed by a stress, but the system soon reaches a new equilibrium. </li></ul><ul><li>Le Châtelier’s principle states that when a system at equilibrium is disturbed, the system adjusts in a way to reduce the change. </li></ul>
  29. 37. Le Chatelier’s Principle <ul><li>Chemical equilibria respond to three kinds of stress: </li></ul><ul><ul><li>changes in the concentrations of reactants or products </li></ul></ul><ul><ul><li>changes in temperature </li></ul></ul><ul><ul><li>changes in pressure </li></ul></ul><ul><li>When a stress is first applied to a system, equilibrium is disturbed and the rates of the forward and backward reactions are no longer equal. </li></ul>
  30. 38. Le Chatelier’s Principle <ul><li>The system responds to the stress by forming more products or by forming more reactants. </li></ul><ul><li>A new chemical equilibrium is reached when enough reactants or products form. </li></ul><ul><li>At this point, the rates of the forward and backward reactions are equal again. </li></ul>
  31. 40. Concentrate <ul><li>Increase the amount of reactants, the equilibrium will shift towards products. </li></ul><ul><li>Increase the amount of products, the equilibrium will shift towards the reactants. </li></ul>
  32. 41. Getting Hot! <ul><li>If the forward reaction is exothermic, cooling the system will force the reaction forward. </li></ul><ul><li>If the forward reaction is endothermic, heating the system will force the reaction forward. </li></ul>
  33. 42. Feel the Pressure <ul><li>Increasing pressure will shift the equilibrium to the side with less atoms. </li></ul>
  34. 44. Practical Le Chatelier <ul><li>The chemical industry makes use of Le Châtelier’s principle in the synthesis of ammonia by the Haber Process. </li></ul><ul><li>High pressure is used to drive the following equilibrium to the right . </li></ul>
  35. 45. Chapter 15 Acids and Bases
  36. 46. Acids <ul><li>These substances can recognized as acidic by their tart, sour, or sharp taste. </li></ul><ul><li>These substances contain dissolved compounds that chemists describe as acids . </li></ul><ul><li>Many other acids, such as sulfuric acid or hydrochloric acid, are highly caustic and should not be put to the taste test. </li></ul>
  37. 47. Acids <ul><li>Acids are electrolytes, so their solutions in water are conductors of electric current. </li></ul><ul><li>Like other electrolytes, hydrogen chloride dissociates to produce ions. </li></ul><ul><li>HCl( g ) + H2O( l )  H3O+( aq ) + Cl−( aq ) </li></ul><ul><li>The hydronium ion, H3O+, is able to transfer charge through aqueous solutions much faster than other ions do. </li></ul>
  38. 49. Acids <ul><li>Another property shared by aqueous solutions of acids is that they react with many metals. </li></ul><ul><li>All metals that are above hydrogen in the activity series react with acids to produce hydrogen gas. </li></ul><ul><li>2H3O+( aq ) + Zn( s )  2H2O( l ) + H2( g ) + Zn2+( aq ) </li></ul>
  39. 50. Acids <ul><li>Some electrolytes are strong and others are weak, depending on whether they dissociate completely or partially. </li></ul><ul><li>When a weak acid is dissolved in water, only a small fraction of its molecules are ionized at any given time. </li></ul>
  40. 51. Bases <ul><li>Bases are another class of electrolytes. Unlike acids, which are usually liquids or gases, many common bases are solids. </li></ul><ul><li>Solutions of bases are slippery to the touch, but touching bases is an unsafe way to identify them. </li></ul><ul><ul><li>The slippery feel comes about because bases react with oils in your skin, converting them into soaps. </li></ul></ul>
  41. 52. Bases <ul><li>Some bases, such as magnesium hydroxide, Mg(OH)2, are almost insoluble in water. </li></ul><ul><li>Other bases, such as potassium hydroxide, are so soluble that they will absorb water vapor from the air and dissolve in the water. </li></ul><ul><li>A base that is very soluble in water is called an alkali, a term that describes the Group 1 metals of the periodic table. </li></ul>
  42. 53. Bases <ul><li>The alkali metals react with water to form hydroxides that are water-soluble alkalis. These are called basic or Alkaline. </li></ul><ul><li>Just as acids may be strong or weak depending on whether they ionize completely or reach an equilibrium between ionized and un-ionized forms, bases are also classified as strong or weak. </li></ul>
  43. 54. Bases <ul><li>Both strong and weak bases generate hydroxide ions when they dissolve in water. </li></ul><ul><li>Many oxides, carbonates, and phosphates are bases, too. </li></ul>
  44. 55. Classifications <ul><li>Arrhenius acid – Produces Hydronium ions </li></ul><ul><li>Arrhenius Base – Produces Hydroxide ions </li></ul>
  45. 56. Classification <ul><li>Brønsted-Lowry acids – Donate Protons </li></ul><ul><li>Brønsted-Lowry acids – Accept Protons </li></ul>
  46. 57. Conjugate Acids and Bases Look again at the equation for the reversible reaction of ammonia, NH 3 , with water: <ul><ul><ul><li>base acid c. acid c. base </li></ul></ul></ul><ul><li>Water donates a proton to ammonia, so it is an acid. </li></ul><ul><li>Ammonia accepts the proton, so it is a base. </li></ul>
  47. 58. Amphoteric <ul><li>Some species are both an acid and a base and can both donate and accept protons. </li></ul><ul><li>Such species are described as amphoteric. </li></ul><ul><li>Amphoteric describes a substance, such as water, that has the properties of an acid and the properties of a base. </li></ul>
  48. 60. Self-Ionization <ul><li>Water is both an acid and a base. It both gives and receives protons. </li></ul>[H3O+] = [OH−] = 1.00 × 10 −7 M
  49. 61. Self-Ionization <ul><li>An equilibrium-constant expression relates the concentrations of species involved in an equilibrium. </li></ul><ul><li>The relationship for the water equilibrium is simply </li></ul><ul><li>[H3O+][OH−] = Kw </li></ul>
  50. 62. <ul><li>The value of Kw can be found from the known concentrations of the hydronium and hydroxide ions in pure water. </li></ul><ul><li>Kw = (1.00 × 10 −7 )(1.00 × 10 −7 ) = 1.00 × 10 −14 </li></ul><ul><li>The product of these two ion concentrations is always a constant. </li></ul>
  51. 64. Chapter 15 pH, or more math!
  52. 65. Meaning of pH <ul><li>When acidity and basicity are exactly balanced such that he numbers of H 3 O + and OH − ions are equal, we say that the solution is neutral. </li></ul><ul><li>Pure water is neutral because it contains equal amounts of the two ions. </li></ul>
  53. 66. Meaning of pH <ul><li>A solution made by dissolving 0.100 mol of NaOH in 1.00 L of water has a hydroxide ion concentration of 0.100 M. </li></ul><ul><li>The hydronium ion concentration can be calculated using Kw . </li></ul>
  54. 67. Meaning of pH <ul><li>In 1909, Danish chemist Søren Sørensen proposed using the negative logarithm of [H 3 O + ] as the index of basicity and acidity. </li></ul><ul><li>He called this measure the pH or p ower of H ydrogen. </li></ul><ul><li>pH can be calculated by the following mathematical equation: </li></ul><ul><li>pH = −log [H 3 O + ] OR [H 3 O + ] = 10 −pH </li></ul>
  55. 68. The Meaning of pH, continued Calculating pH from [H 3 O + ], continued <ul><li>The pH equation may be rearranged to calculate the hydronium ion concentration from the pH. </li></ul><ul><li>[H 3 O + ] = 10 −pH </li></ul><ul><li>Because pH is related to powers of 10, a change in one pH unit corresponds to a tenfold change in the concentrations of the hydroxide and hydronium ions. </li></ul>Section 2 Acidity, Basicity, and pH Chapter 15