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Chemical Solutions

Chemical Solutions. Homework: Textbook Read pages 501 – 507 Answer Questions on Page 508 # 3, 5, 6, 7. Definition. A homogeneous mixture of a solute dissolved in a solvent. Parts of Solutions. Solute – material that is dissolved Ex) iced tea mix, sugar, NaCl

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Chemical Solutions

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  1. Chemical Solutions Homework: Textbook Read pages 501 – 507 Answer Questions on Page 508 # 3, 5, 6, 7

  2. Definition • A homogeneousmixture of a solute dissolved in a solvent

  3. Parts of Solutions • Solute – material that is dissolved Ex) iced tea mix, sugar, NaCl 2. Solvent – substance that does the dissolving Ex) water (for aqueous solutions), ethanol, hexane

  4. Types of solutions 1. Electrolyte Def: a substance that dissolves in water to give a solution that conducts an electric current Typically formed from a soluble ioniccmpd and highly polar substances, when positive and negative ions separate from one another

  5. 2.Nonelectrolyte –a substance that when dissolved will not conduct an electric current • when dissolved substance yields molecules in solution, not ions

  6. 3. Solutions formed in all 3 states • Gaseous slns – gases easily disperse the solute • evaporated substances, air is a solvent • air is a solution of several gases • sulfur vapor is a solid – gas solution

  7. b. Liquid solutions • soda is a liquid – gas solution • alcohol and water is a liquid – liquid sln • sugar water is a solid – liquid sln

  8. c. Solid solutions • many metal objects are solid sln • Alloys are mixtures in which the solids of two or more elements are uniformly mixed Ex) sterling silver – 92% Ag and 8% Cu Brass – Cu and Zn

  9. D. Dissolving process 1. Solvation – the process by which solvent particles surround solute particles • if the solvent is water the process is called hydration

  10. Watch the dissolving process • water is a polar molecule, therefore the opposite ends of the water molecule attract to the different ions

  11. 3. LIKES DISSOLVE LIKES • polar solvents will dissolve ionic solutes and polar molecules • nonpolar solvents will dissolve nonpolar solutes ex) Benzene (C6H6), ethanol (C2H5OH)

  12. 4. Heat of solution Def: the amt of heat energy lost or gained as a substance dissolves • Table I (DH in kJ) ( minus sign indicates exothermicrxn) • if the solution gets warmer, heat is released (exo) • if solution gets colder, heat is absorbed (endo)

  13. Solubility Def: The amount of a solute that will dissolve in a given amount of a solvent

  14. Factors affecting the rate of dissolving • Dissolving occurs at the surface of a solute • anything that increases the amt of solute coming into contact with the solvent increases rate of dissolving

  15. Factors affecting the rate of dissolving increase surface area • more solute particles bombarded with solvent particles

  16. Factors affecting the rate of dissolving • agitate the solution • - disperses dissolved solute

  17. Factors affecting the rate of dissolving • heat the solvent • increase the KE of solvent particles • more frequent collisions, removing more particles from solid

  18. Factors that affect solubility a. Temperature inc temp, more collisions between solute and solvent particles Solids in liquids – as temp of solvent inc, the solubility of solids increases Gases in Liquids – as temp of solvent inc, the solubility of a gas decreases

  19. Factors that affect solubility • Pressure • changes in pressure have no effect on a solid dissolved in a liquid • Henry’s law – if the temp is held constant, the solubility of a gas in liquid is directly proportional to the pressure of that gas above the liquid

  20. Factors that affect solubility • Types of solutes and solvents • Miscible liquids - 2 liquids that are mutually soluble • Ex) ethanol and water • Immiscible liquids – 2 liquids that are not soluble in one another • Ex) oil and water

  21. Solution equilibrium • occurs when the opposing processes of dissolving and crystallization of a solute occur at an equal rate Solute + solvent  solution

  22. Saturated solution • a solution that contains the max amt of dissolved solute • a saturated solution is in a state of dynamicequilibrium

  23. Unsaturated solution • – a solution that contains less solute than a saturated sln under the same conditions of temp and press

  24.  Supersaturated solution • a sln that contains more dissolved solute than a saturated sln under the same conditions

  25. Solubility Curve (Table G) • Plot of the # of grams of each cmpd that will dissolve at diff. Temps in 100 grams of H2O • Each line represents the point at which a solution would be saturated.

  26. Helpful hints • - when asked to determine the # of grams of solute needed to make a saturated solution in 100 g of H2O at a specific temperature, refer to Table G • - if the number of grams of water is any value other than 100 g, set up a proportion in the following manner: Mass of solute from chart = unknown from question 100 g water mass of water from question

  27. Practice Problems According to Reference Table G, which solution is saturated at 30°C? • (1) 12 grams of KClO3 in 100 grams of water • (2) 12 grams of KClO3 in 200 grams of water • (3) 30 grams of NaCl in 100 grams of water • (4) 30 grams of NaCl in 200 grams of water

  28. Practice Problems A student uses 200 grams of water at a temperature of 60°C to prepare a saturated solution of potassium chloride, KCl. According to Reference Table G, how many grams of KCl must be used to create this saturated solution?

  29. Homework answers • 8. a.105 g • b. 47g • c. 58 g • 9. 5 g KNO3 • 10. 22 g • 11. 11 • 12. a. unsaturated • b. Supersaturated • c. Saturated • d. Saturated • KClO3 • KNO3 • NaCl • 17 g • 73⁰C • NaCl & NH4Cl or KCl & KNO3 • 220 g

  30. Concentrations Def: refers to the amt of solute present in a given amt of solution Qualitative Descriptions • Dilute – a sln that contains a relatively small quantity of dissolved solute • Concentrated – a sln that contains a relatively large amt of dissolved solute

  31. Molarity • measurement of concentration in terms of moles of solute per liter of solution • Molarity = # moles solute Liters of solution • a sln that contains 1 mole of solute per liter of solution is called a 1 molarsln = 1M

  32. What is the molarity of a sln that contains 4.9 g of H2SO4 (98g/mol) in 250 mL of sln?

  33. How many moles of KNO3 are contained in 300 mL of a 0.50 M sln? How many grams (101g/mol)?

  34. What is the molarity of a solution which contains 120 g of NaOH(40g/mol) in 2000g of solution?

  35. Homework Answers Even

  36. Homework AnswersOdd

  37. Percent Solute by Weight • % solute by weight is # grams of solute per 100g of solution % solute = mass solute x 100 mass of solution

  38. Practice Problems • What is the % solute by weight in the solution in which 20 g of NaCl is dissolved in 80 g of water?

  39. Practice Problems • Calculate the % by mass when 45 g of KNO3 are dissolved in 100g H2O.

  40. Parts per million • very small mass fractions of solutions often expressed in parts per million (ppm) • to express a mass fraction as ppm, multiply it by 1 million ppm • 1 ppm = 1 gram of solute per 1,000,000 grams of solution Formula: ppm = grams solute x 106 grams solution

  41. Practice Problems A sample of groundwater is found to contain 14 mg of barium per Kg of water. What is the concentration in ppm?

  42. Practice Problems If the concentration of Pb+2ions in tap water is found to be 0.025 ppm, what volume of this water would contain 100.0 x 10-6 grams lead?

  43. Who dissolves in water? • Ionic compounds and other polar stuff of course! • How do we know what ionic compounds dissolve? • Table F

  44. Dissociation • the separation of ions that occurs when an ionic compound is dissolved H2O Ex) NaCl(s) Na+(aq) + Cl-(aq) How many moles of ions are produced by one mole of NaCl dissolving? 2 moles of ions

  45. Try another CaCl2 How many moles of ions are produced? CaCl2 Ca2+(aq) + 2Cl-(aq) 3 moles

  46. Hows about this one? C6H12O6 How many moles of particles are produced when one mole of glucose dissolves? C6H12O6(s)C6H12O6(aq) One, it’s the loneliest number

  47. Colligative properties • properties of solutions that are effected by the number of particles dissolved • the more dissolved particles the greater the effect on the colligative property CaCl2(s) Ca+2(aq) + 2 Cl-(aq) Electrolyte C6H12O6(s)  C6H12O6(aq) Nonelectrolyte

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