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Chapter 15

Chapter 15. Solutions. Objectives. To understand the process of dissolving To learn why certain substances dissolve in water To learn qualitative terms describing the concentration of a solution To understand the factors that affect the rate at which a solid dissolves. What is a solution?.

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Chapter 15

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  1. Chapter 15 Solutions

  2. Objectives • To understand the process of dissolving • To learn why certain substances dissolve in water • To learn qualitative terms describing the concentration of a solution • To understand the factors that affect the rate at which a solid dissolves

  3. What is a solution? • Solution – homogeneous mixture • Solvent – substance present in largest amount • Solutes – other substances in the solution • Aqueous solution – solution with water as the solvent

  4. A. Solubility Review • Solubility of Ionic Substances • Ionic substances breakup into individual cations and anions.

  5. A. Solubility • Solubility of Ionic Substances • Polar water molecules interact with the positive and negative ions of a salt.

  6. A. Solubility • Solubility of Polar Substances • Ethanol is soluble in water because of the polar OH bond.

  7. A. Solubility • Solubility of Polar Substances • Why is solid sugar soluble in water?

  8. A. Solubility • Substances Insoluble in Water • Nonpolar oil does not interact with polar water. • Water-water hydrogen bonds keep the water from mixing with the nonpolar molecules.

  9. A. Solubility • How Substances Dissolve • A “hole” must be made in the water structure for each solute particle. • The lost water-water interactions must be replaced by water-solute interactions. • “like dissolves like”

  10. H2O, The Universal Solvent Much of chemistry that affects each of us occurs among substances dissolved in water. Virtually all chemistry that makes life possible occurs in an aqueous environment. Aqueous Solution: a solution in which water is the dissolving medium or solvent. Solvent: the dissolving medium in a solution. Solute: a substance dissolved in a liquid to form a solution.

  11. H2O, The Bent Universal Solvent Waters polar characteristics: Electrons that are shared spend more of their time with the oxygen atom

  12. H2O, The Universal Solvent Hydration: hydration of ions tends to cause salts to “fall apart” or dissolve. Water pulls salts apart using it’s polarity http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/graphics/nacl2.gif

  13. Some Properties of Water 1. Water is “bent” or V-shaped. 2. The O-H bonds are covalent. 3. Water is a polar molecule. 4. Hydration occurs when salts dissolve in water.

  14. A Solute: • Dissolves in water (or other “solvent”) • Changes phase(if different from the solvent) • Is present in lesser amount (if the same phase as the solvent)

  15. A Solvent: • Retains its phase(if different from the solute) • Is present in greater amount (if the same phase as the solute)

  16. Electrical Conductivity: the ability to conduct electricity in solution Strong Electrolytes: (HCl) Solution that conducts electricity efficiently Weak Electrolytes: (Vinegar) Solution that conducts electricity inefficiently Non Electrolytes: (Sugar) Solution that prevents the flow of electricity

  17. Electrolytes in the Body • Carry messages to and from the brain as electrical signals • Maintain cellular function with the correct concentrations electrolytes

  18. Electrolytes Strong - conduct current efficiently NaCl, HNO3 Weak- conduct only a small current vinegar, tap water Non - no current flows pure water, sugar solution

  19. Acids Strong acids -dissociate completely to produce H+in solution hydrochloric and sulfuric acid Weak acids - dissociate to a slight extent to give H+in solution acetic and formic acid

  20. Bases Strong bases- react completely with water to give OHions. sodium hydroxide Weak bases- react only slightly with water to give OHions. ammonia

  21. H2O, The Universal Solvent It is very important to recognize that when an ionic substance dissolves in water they break up into the individual cations and anions. Example: Ammonium Nitrate in water: Can you draw the ions associated with ammonium nitrate? When cations and anions have been dissolved in solution they move around independently

  22. H2O, The Universal Solvent Solubility: the amount of substance that dissolves in a given volume of solvent at a given temperature The solubility of substances in water varies greatly. For ionic compounds it depends on the relative attraction between the ions. “Like dissolves Like”, in general polar or ionic compounds are expected to be soluble in water than non polar substances

  23. Solubility Review: Rules for Solubility 1. Most nitrate (NO3-) salts are soluble 2. Most salts containing the alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4+) are soluble 3. Most Chloride, Bromide, and Iodide salts are soluble. Exceptions: those containing Ag+, Pb2+, and Hg22+ 4. Most sulfate ions are soluble. Exceptions: BaSO4, PbSO4, Hg2SO4 and CaSO4 5. Most hydroxide salts are insoluable. Exceptions: NaOH and KOH are soluble 6. Most Sulfide (S2-), carbonate (CO32-), chromate (CrO42-) and phosphates (PO43-) are insoluable

  24. Solubility Practice • Show the ions . • AgNO3(aq)  • Na3PO4(aq)  • BaCl2(aq)  • FeCl3(aq)  • NaOH(aq)  • CuSO4(aq) 

  25. Solubility Practice Answers • Show the ions. • AgNO3(aq)  Ag+ + NO3- • Na3PO4(aq) PO43- + 3 Na+ • BaCl2(aq)  2 Cl- + Ba2+ • FeCl3(aq)  Fe3+ + 3Cl- • NaOH(aq)  Na+ + OH- • CuSO4(aq)  SO42- + Cu2+

  26. B. Solution Composition: An Introduction • The solubility of a solute is limited. • Saturated solution – contains as much solute as will dissolve at that temperature • Unsaturated solution – has not reached the limit of solute that will dissolve

  27. B. Solution Composition: An Introduction • Supersaturated solution – occurs when a solution is saturated at an elevated temperature and then allowed to cool but all of the solid remains dissolved • Contains more dissolved solid than a saturated solution at that temperature • Unstable – adding a crystal causes precipitation

  28. A solution is a homogeneous mixture of 2 or more substances in a single phase. One constituent is usually regarded as the SOLVENTand the others as SOLUTES.

  29. Solution Definitions Classified as saturatedor unsaturated. A saturated solution contains the maximum quantity of solute that dissolves at that temperature. An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

  30. SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved Supersaturated solutions are unstable. The supersaturation is only temporary, and usually accomplished in one of two ways: • Warm the solvent so that it will dissolve more, then cool the solution • Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.

  31. Supersaturated : Sodium Acetate • One application of a supersaturated solution is the sodium acetate “heat pack.”

  32. Solubility Curves How to interpret a graphical representation of solute in solvent.

  33. Saturated Solubility curve Supersaturated Unsaturated

  34. Any point on a line represents a saturated solution. • In a saturated solution, the solvent contains the maximum amount of solute. • Example • At 90oC, 40 g of NaCl(s) in 100g H2O(l) represent a saturated solution.

  35. Any point below a line represents an unsaturated solution. • In an unsaturated solution, the solvent contains less than the maximum amount of solute. • Example • At 90oC, 30 g of NaCl(s) in 100g H2O(l) represent an unsaturated solution. 10 g of NaCl(s) have to be added to make the solution saturated.

  36. Solubility Curve • Any point above a line represents a supersaturated solution. • In a supersaturated solution, the solvent contains more than the maximum amount of solute. A supersaturated solution is very unstable and the amount in excess can precipitate or crystallize. • Example • At 90oC, 50 g of NaCl(s) in 100g H2O(l) represent a supersaturated solution. Eventually, 10 g of NaCl(s) will precipitate.

  37. Solubility curve Any solution can be made saturated, unsaturated, or supersaturated by changing the temperature.

  38. How many grams of potassium bromide (KBr) candissolve in 100 grams of water at 20°C? Answer: 70 grams of KBr can dissolve in 100g of water at 20°C 70g

  39. How many grams of potassium nitrate (KNO3) can dissolve in 100 g of water at 60°C? 130g

  40. How many grams of potassium bromide (KBr) can dissolve in 100 g of water at 20°C? 70 g

  41. How many grams of sodium chloride (NaCl) can dissolve in 100 g of water at 100°C? 40 g

  42. How many grams of sodium chlorate (NaClO3) can dissolve in 200 g of water at 80°C? 200 g 200g per 100 g of water, so in 200 g of water we will have to double it: 200x2=400 g NaClO3 can be dissolved in 200 g of water at 80°C

  43. At what temperature can 150 grams of potassium nitrate (KNO3) dissolve in 100 g of water? 65° C Answer: 150 grams of Potassium nitrate can be dissolved in 100 g of water at 65°C

  44. At what temperature can 100 grams of potassium bromide (KBr) dissolve in 100 g of water? 82° C Answer: 100 g of potassium bromide can dissolve in 100 g of water at 82°C

  45. B. Solution Composition: An Introduction • Solutions are mixtures. • Amounts of substances can vary in different solutions. • Specify the amounts of solvent and solutes • Qualitative measures of concentration • concentrated – relatively large amount of solute • dilute – relatively small amount of solute

  46. B. Solution Composition: An Introduction • Which solution is more concentrated?

  47. B. Solution Composition: An Introduction • Which solution is more concentrated?

  48. C. Factors Affecting the Rate of Dissolving • Surface area • Stirring • Temperature

  49. Objectives • To understand mass percent and how to calculate it • To understand and use molarity • To learn to calculate the concentration of a solution made by diluting a stock solution

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