1. Chapter 8 Solutions, Acids, and Bases

2. 8.1 Formation of SolutionsSolutions, Acids, and Bases 8.1 Formation of Solutions  Any state of matter – solid, liquid, or gas – can become part of a solution.  For a solution substance must dissolve in another.

3. 8.1 Formation of SolutionsSolutions, Acids, and BasesDissolving  A solution is a homogenous mixture of two or more substances.  Every solution has two types of components.  A solute is a substance whose particles are dissolved in a solution  The substance in which the solute is dissolved is called the solvent.

4. 8.1 Formation of SolutionsSolutions, Acids, and Bases  The solution takes the state of the solvent.  Figure 2 lists some common solutions and the states of their solutes and solvents.  For example nitrogen, 78% of air, is the solvent.  Oxygen, carbon dioxide, argon, and other gases are the solutes.

5. 8.1 Formation of SolutionsSolutions, Acids, and Bases  Substances can dissolve in water in three ways – dissociation, dispersion, and ionization.

6. 8.1 Formation of SolutionsSolutions, Acids, and Bases Dissociation of Ionic Compounds  For a solute to dissolve in water, the solute and solvent particles must attract one another.  The particles within the solute are attracted to one another.  The particles within the solvent are attracted to one another.

7. 8.1 Formation of SolutionsSolutions, Acids, and Bases  Before a solution can form, the attractions that hold the solute together and the solvent together must be overcome.  Figure 3 illustrates how NaCl crystals dissolve in water.  NaCl is an ionic compound.  Water is a polar molecule and is attracted to the ions in solute.

8. 8.1 Formation of SolutionsSolutions, Acids, and Bases  The crystal dissolves as the Na + and Cl − ions are pulled into solution by the surrounding water molecules.  The process in which an ionic compound separates into ions as it dissolves is called dissociation.

9. 8.1 Formation of SolutionsSolutions, Acids, and Bases

10. 8.1 Formation of SolutionsSolutions, Acids, and Bases

11. 8.1 Formation of SolutionsSolutions, Acids, and Bases Dispersion of Molecular Compounds  Sugar dissolves in water by dispersion, or breaking into small pieces that spread throughout the water.  Both sugar and water are polar molecules, so they attract one another.  Because the water molecules are constantly moving, they collide frequently with the sugar crystals.

12. 8.1 Formation of SolutionsSolutions, Acids, and Bases  When enough water molecules have surrounded a sugar molecule, the attractions between them are enough to overcome the attractions holding the sugar molecule to the crystal.  The sugar molecule breaks free, and is pulled into solution.

13. 8.1 Formation of SolutionsSolutions, Acids, and Bases Ionization of Molecular Compounds  Hydrogen chloride is a molecular compound in which a hydrogen atom and a chlorine atom share a pair of electrons.  When HCl gas dissolves in water, the H + from each HCl molecule is transferred to a water molecule.  For each HCl molecule that reacts, a hydronium ion, H 3 O +, and a chloride ion, Cl −, are produced.

14. 8.1 Formation of SolutionsSolutions, Acids, and Bases  When hydrogen chloride and water form a solution, two molecular compounds react to form two ions.  The process in which neutral molecules gain or lose electrons is known as ionization.

15. 8.1 Formation of SolutionsSolutions, Acids, and Bases  Unlike dissociation and dispersion, which are physical changes, ionization is a chemical change.  When a solute dissolves by dissociation, the ions pulled into solution are the ions present in the solute.  When a solute dissolves by ionization, the ions in solution are formed by the reaction of solute and solvent particles.

16. 8.1 Formation of SolutionsSolutions, Acids, and Bases Properties of Liquid Solutions  Three physical properties of a solution that can differ from those of its solute and solvent are  conductivity  freezing point  boiling point

17. 8.1 Formation of SolutionsSolutions, Acids, and BasesConductivity  The ions in solution will conduct an electric current.

18. 8.1 Formation of SolutionsSolutions, Acids, and Bases Freezing Point and Boiling Point  Figure 6A shows how ice forms when water molecules are able to arrange themselves in a rigid structure.  Figure 6B shows how the presence ions interferes with the freezing process.  Water at sea level freezes at 0 o C.  Salt solutions can have a freezing point as low as −15 o C.

19. 8.1 Formation of SolutionsSolutions, Acids, and Bases  A solute can also raise the boiling point of the solvent.  Ethylene glycol, C 2 H 6 O 2, raises the boiling point and is used as a coolant in car radiators to prevent overheating.

20. 8.1 Formation of SolutionsSolutions, Acids, and Bases Heat of Solution  During formation of a solution, energy is either released or absorbed.  Like chemical reactions, the solution process can be described as exothermic or endothermic.  In order for a solution to form, both the attractions among solute particles and the attractions among solvent particles must be broken.

21. 8.1 Formation of SolutionsSolutions, Acids, and Bases  Breaking attractions requires energy.  As the solute dissolves, new attractions form between solute and solvent particles.  The formation of attractions releases energy.  The difference between these energies is known as the heat of solution.

22. 8.1 Formation of SolutionsSolutions, Acids, and Bases Factors Affecting the Rates of Dissolving  Rates of dissolving depend on the frequency and energy of collisions that occur between particles of the solute and solvent.  Factors that affect the rate of dissolving include:  surface area  stirring  temperature

23. 8.1 Formation of SolutionsSolutions, Acids, and Bases

24. 8.1 Formation of SolutionsSolutions, Acids, and Bases  The greater the surface area of a solid solute, the more frequent the collisions are between solute and solvent particles.  More collisions result in a faster rate of dissolving.  The more finely divided a solid solute is, the faster it dissolves.

25. 8.1 Formation of SolutionsSolutions, Acids, and Bases

26. 8.1 Formation of SolutionsSolutions, Acids, and Bases  Stirring moves dissolved particles away from the surface of the solid and allows for more collisions between solute and solvent particles.  Substances dissolve faster when stirred.

27. 8.1 Formation of SolutionsSolutions, Acids, and Bases

28. 8.1 Formation of SolutionsSolutions, Acids, and Bases  Increasing the temperature of the solvent will speed up the rate of reaction by causing the particles to move faster.  The solute goes into solution more quickly because both the number of collisions and the energy of these collisions increase.

29. 8.1 Formation of SolutionsSolutions, Acids, and Bases

30. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases 8.2 Solubility and Concentration

31. Solutions, Acids, and BasesSolubility  The maximum amount of a solute that dissolves in a given amount of solvent at a constant temperature is called solubility.  Solubility is usually expressed in grams of solute per 100 grams of solvent at a specified temperature.

32. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases  Depending on the amount of solute in solution, solutions are described as saturated, unsaturated, or supersaturated.

33. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Saturated Solutions  Table sugar is very soluble in water. At 20 o C, 203.9 g will dissolve in 100 g of water.  If you try to dissolve more sugar in the same amount of water it will not dissolve.  The solution is saturated.  A saturated solution contains as much solute as the solvent can hold at a given temperature.

34. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Unsaturated Solutions  A solution that has less than the maximum amount of solute is called unsaturated.  A solution is unsaturated as long as the amount of solute is less than the solubility at that temperature.

35. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Supersaturated Solutions  A solvent can sometimes dissolve more solute than expected, based on its solubility.  If a solvent is heated above the specified temperature, more solute may dissolve.

36. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases  If the solvent is cooled back to the specified temperature, the extra solute may stay in solution.  A supersaturated solution contains more solute than it can normally hold at a given temperature.  Supersaturated solutions are very unstable.

37. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Factors Affecting Solubility  Solubility varies not only with the solvent used but also with the conditions of the solution process.  Factors that affect the solubility of a solute include:  the polarity of the solvent  temperature  pressure

38. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Polar and Nonpolar Solvents  A common guideline for predicting solubility is ‘like dissolves like.”  Solution formation is more likely to happen when the solute and solvent are either both polar or both nonpolar.

39. 8.2 Solubility and ConcentrationSolutions, Acids, and BasesTemperature  In general, the solubility of solids increases as the temperature of the solvent increases.  Unlike most solids, gases usually become less soluble as the temperature of the solvent increases.

40. 8.2 Solubility and ConcentrationSolutions, Acids, and BasesPressure  To produce a carbonated beverage manufacturers pressure to force CO 2 to dissolve in the liquid.  Increasing the pressure on a gas increases its solubility in a liquid.  The pressure of CO 2 in a sealed can of cola can be two or three times atmospheric pressure.

41. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Concentration of Solutions  The concentration of a solution is the amount of solute dissolved in a specified amount of solution.  Concentration can be expressed as:  percent by volume  percent by mass  molarity

42. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Percent by Volume  Percent by volume is determined by dividing the volume of solute by the volume of solution.

43. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases Percent by Mass  Concentration expressed as a percent by mass is more useful when the solute is a solid.  Percent by mass is the percent of a solution’s total mass that is accounted for by the solute.

44. 8.2 Solubility and ConcentrationSolutions, Acids, and BasesMolarity  To compare the number of solute particles in solutions, chemists often use moles to measure concentration.  A mole is the amount of a substance that contains 6.02 ×10 23 particles of that substance.  Molarity is the number of moles of a solute dissolved per liter of solution.

45. 8.2 Solubility and ConcentrationSolutions, Acids, and Bases  Table sugar, C 12 H 22 O 11, has a molar mass of 342 grams.  To make a 1-molar (1M) solution of table sugar water, add 342 g of sugar to enough water to make one liter of solution.

46. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases 8.3 Properties of Acids and Bases

47. Solutions, Acids, and Bases Identifying Acids  An acid is a compound that produces hydronium (H 3 O + ) ions when dissolved in water.  When hydrogen chloride gas dissolves in water, it ionizes and forms hydronium ions and chlorine gas.  HCl + H 2 O → H 3 O + + Cl −

48. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  Some general properties of acids include:  sour taste  reactivity with metals  ability to produce color changes in indicators.

49. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Sour Taste  Foods that taste sour often contain acids.  For example, lemons, limes, and oranges contain citric acid., C 6 H 8 O 7.  While many foods that are edible contain acids, NEVER test an acid by tasting it.

50. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Reactivity with Metals  The reaction between an acid and a metal is an example of a single- replacement reaction.  Zn + 2HCl → H 2 + ZnCl 2  shows how zinc replaces hydrogen in hydrochloric acid, hydrogen gas and zinc (II) chloride are produced.

51. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Color Changes in Indicators  An indicator is any substance that changes color in the presence of an acid or base.  A common indicator is litmus, a dye derived from lichens.  Blue litmus paper turns red in the presence of an acid.

52. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  If an unknown solution is dropped on blue litmus paper and the paper turns red, the solution can be classified as an acid.

53. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Acetic acid CH 3 COOH Vinegar Carbonic acid H 2 CO 3 Carbonated beverages Hydrochloric acid HCI Digestive juices in stomach Nitric acid HNO 3 Fertilizer production Phosphoric acid H 3 PO 4 Fertilizer production Sulfuric acid H 2 SO 4 Battery acid

54. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Identifying Bases  A base is a compound that produces hydroxide ions (OH − ) when dissolved in water.  When sodium hydroxide dissolves in water, it dissociates into sodium ions and hydroxide ions.  NaOH → Na + + OH −

55. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  Some general properties of bases include:  bitter taste  slippery feel  the ability to produce color changes in indicators.

56. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  Unlike acids, bases usually do not react with metals.  Low reactivity with metals is not considered a general property of bases.

57. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Bitter Taste  Unsweetened chocolate tastes bitter due to the presence of a base called theobromine, C 7 H 8 N 4 O 2.

58. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Slippery Feel  Bases feel slippery.  Wet soap and many cleaning products that contain bases are slippery to the touch.  Some wet rocks feel slippery because the water dissolves compounds in the rocks and produces a basic solution.

59. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Aluminum hydroxide Al(OH) 3 Deodorant, antacid Calcium hydroxide Ca(OH) 2 Concrete, plaster Magnesium hydroxide Mg(OH) 2 Antacid, laxative Sodium hydroxide NaOH Drain cleaner, soap production

60. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Color Changes in Indicators  Bases turn red litmus paper blue.  Phenolphthalein is another example of an acid-base indicator.  In a solution containing a base, phenolphthalein is red.  In a solution containing an acid, phenolphthalein is colorless.

61. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  The plant, hydrangea, is a natural indicator.  When grown in acidic soil, hydrangeas have bluish-purple flowers.  When they are grown in basic soil, the flowers are pink.

62. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases

63. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases

64. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Neutralization and Salts  The reaction between an acid and a base is called neutralization.  During neutralization, the negative ions in an acid compound combine with the positive ions in a base to produce an ionic compound called a salt.

65. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  At the same time, the hydronium ions from the acid combine with the hydroxide ions from the base to produce water.  The neutralization reaction between an acid and a base produces a salt and water.

66. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Sodium chloride NaCl Food flavoring, preservative Sodium carbonate Na 2 CO 3 Used to make glass Potassium chloride KCl Used as a salt substitute to reduce dietary intake of sodium Potassium iodide Kl Added to table salt to prevent iodine deficiency Magnesium chloride MgCl 2 De-icer for roads Calcium carbonate CaCO 3 Chalk, marble floors, and tables Ammonium nitrate NH 4 NO 3 Fertilizer, cold packs

67. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases Proton Donors and Acceptors  Hydronium ions are produced when acids dissolve in water.  When an acid and a base react in water, a proton from the hydronium ion from the acid combines with the hydroxide ion from the base to form water.

68. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  Acids lose, or “donate” protons.  Bases “accept” protons forming water.  Acids can be defined as proton donors and bases can be defined as proton acceptors.  This definition allows a wider range of substances to be classified as acids or bases.

69. 8.3 Properties of Acids and BasesSolutions, Acids, and Bases  Based on earlier definitions water is neither an acid nor a base.  Using the proton-donor or proton- acceptor definition, water can be either an acid or a base depending on the compound with which it reacts.

70. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases 8.4 Strength of Acids and Bases  One way to describe the acidity or basicity is to determine the concentration of hydronium or hydroxide ions present in solution.  Another way is to describe how readily those ions are formed.

71. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases The pH Scale  Chemists use a number scale from 0 to 14 to describe the concentration of hydronium ions in a solution.  It is known as the pH scale.  The pH of a solution is a measure of its hydronium ion concentration.

72. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases The pH Scale

73. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  A pH of 7 indicates a neutral solution.  Acids have a pH less than 7.  Bases have a pH greater than 7.  Distilled water falls in the middle of the pH scale.

74. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases   Water ionizes slightly.  2H 2 O H 3 O + + OH −  The arrow to the left is longer than the arrow to the right showing that water contains more molecules than ions.

75. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  Water is neutral because is has equal concentrations of hydronium and hydroxide ions.

76. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  If an acid is added to water, the concentration of H 3 O + increases and the concentration of OH − decreases.  The lower the pH value, the greater the H 3 O + ion concentration in solution is.

77. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  If a base is added to water, the concentration of OH − increases and the concentration of H 3 O + decreases.  The higher the pH value, the lower the H 3 O + ion concentration is.

78. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases Strong Acids and Bases  Some reactions go to completion while others reach equilibrium.  When certain acids and bases dissolve in water, the formation of ions from the solute almost goes to completion.  Such acids and bases are classified as strong.

79. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases Strong Acids  Hydrochloric acid is a strong acid.  When hydrogen chloride dissolves in water, almost all of its molecules ionize.  When strong acids dissolve in water, they ionize almost completely.  Other strong acids include: sulfuric acid (H 2 SO 4 ), and nitric acid (HNO 3 ).

80. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases Strong Bases  Sodium hydroxide is an example of a strong base.  When dissolved in water, sodium hydroxide almost completely dissociates into sodium and hydroxide ions.  Strong bases dissociate almost completely in water.

81. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  Other strong bases include calcium hydroxide {Ca(OH) 2 }, and potassium hydroxide (KOH).

82. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases Weak Acids and Bases  Weak acids and bases ionize or dissociate only slightly in water.

83. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases Weak Acids  A weak acid forms fewer hydronium ions than a strong acid of the same concentration and has a higher pH than a strong acid.  Concentration is the amount of solute dissolved in a given amount of solution.  Strength refers to the solute’s tendency to form ions in water.

84. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  A strong acid may not have a low pH because concentration also affects pH value.  For example, a dilute solution of HCl can have a pH of 6 and a concentrated solution of CH 3 COOH can have a pH of 3.

85. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases Weak Bases  When ammonia, NH 3, dissolves in water very little ionizes.  It produces few hydroxide ions and makes a weak base.

86. 8.4 Strength of Acids and BasesSolutions, Acids, and BasesBuffers  Weak acids and bases can be used to make buffers.  A buffer is a solution that is resistant to large changes in pH.  Buffers can be prepared by mixing  a weak acid and its salt  a weak base and its salt.

87. 8.4 Strength of Acids and BasesSolutions, Acids, and BasesElectrolytes  An electrolyte is a substance that ionizes or dissociates when it dissolves in water.  The electrolytes in sports drinks help restore balance of ions in the body.

88. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  Strong acids and bases are strong electrolytes because they dissociate or ionize almost completely in water.  Salts also make strong electrolytes.

89. 8.4 Strength of Acids and BasesSolutions, Acids, and Bases  Space shuttles use fuel cells to provide electricity.  The fuel cells use the strong base potassium hydroxide as an electrolyte.  The fuel cells use oxygen and hydrogen instead of metal electrodes.  The fuel cells also produce water.