Mec chapter 6

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MEC Chapter 6

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Mec chapter 6

  1. 1. Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 6 SolutionsDennistonToppingCaret7th Edition
  2. 2. 6.1 Properties of Solutions• Solution - homogeneous mixture• Solute - the substance in the mixture present in lesser quantity• Solvent - the substance present in the largest quantity• Aqueous solution - solution where the solvent is water• Solutions can be liquids as well as solids and gases
  3. 3. 6.1 Properties of Solutions Examples of Solutions • Air - oxygen and several trace gases are dissolved in the gaseous solvent, nitrogen • Alloys - brass and other homogeneous metal mixtures in the solid state • Focus on liquid solutions as many important chemical reactions take place in liquid solutions
  4. 4. 6.1 Properties of Solutions General Properties of Liquid Solutions • Clear, transparent, no visible particles • May have color • Electrolytes are formed from solutes that are soluble ionic compounds • Nonelectrolytes do not dissociate NaCl(s ) H→ Na + (aq ) + Cl- (aq ) 2O • Volumes of solute and solvent are not additive – 1 L ethanol + 1 L water does not give 2 L of solution
  5. 5. 6.1 Properties of Solutions Solutions and Colloids • Colloidal suspension - contains solute particles which are not uniformly distributed – Due to larger size of particles (1nm - 200 nm) – Appears identical to solution from the naked eye – Smaller than 1 nm, have solution – Larger than 1 nm, have a precipitate
  6. 6. 6.1 Properties of Solutions Degree of Solubility • Solubility - how much of a particular solute can dissolve in a certain solvent at a specified temperature • Factors which affect solubility: 1 Polarity of solute and solvent • The more different they are, the lower the solubility 2 Temperature • Increase in temperature usually increases solubility 3 Pressure • Usually has no effect • If solubility is of gas in liquid, directly proportional to applied pressure
  7. 7. 6.1 Properties of Solutions Saturation • Saturated solution - a solution that contains all the solute that can be dissolved at a particular temperature • Supersaturated solution - contains more solute than can be dissolved at the current temperature • How is this done? • Heat solvent, saturate it with solute then cool slowly • Sometimes the excess will precipitate out • If it doesn’t precipitate, the solution will be supersaturated
  8. 8. 6.1 Properties of Solutions Solubility and Equilibrium • If excess solute is added to a solvent, some dissolves • At first, rate of dissolution is large • Later, reverse reaction – precipitation – occurs more quickly • When equilibrium is reached the rates of dissolution and precipitation are equal, there is some dissolved and some undissolved solute • A saturated solution is an example of a dynamic equilibrium
  9. 9. 6.1 Properties of Solutions Solubility of Gases: Henry’s Law • Henry’s law – the number of moles of a gas dissolved in a liquid at a given temperature is proportional to the partial pressure of the gas above the liquid • Gas solubility in a liquid is directly proportional to the pressure of the gas in the atmosphere in contact with the liquid • Gases are most soluble at low temperatures • Solubility decreases significantly at higher temperatures – Carbonated beverages – CO2 solubility less when warm – Respiration – facilitates O2 and CO2 exchange in lungs
  10. 10. 6.2 Concentration Based on Mass 6• Concentration - amount of solute dissolved in a given amount of solution• Concentration of a solution has an effect on – Physical properties • Melting and boiling points – Chemical properties • Solution reactivity
  11. 11. 6.2 Concentration Based on Weight/Volume Percent • Amount of solute = mass of solute in grams • Amount of solution = volume in milliliters amount of solute concentration = Mass amount of solution • Express concentration as a percentage by multiplying ratio by 100% = weight/volume percent or % (W/V) W grams of solute % = ×100% V milliliters of solution
  12. 12. 6.2 Concentration Based on Calculating Weight/Volume Percent Calculate the percent composition or % (W/V) of 2.00 x 102 mL containing 20.0 g sodium chloride 20.0 g NaCl, mass of solute Mass 2.00 x 102 mL, total volume of solution % (W/V) = 20.0g NaCl / 2.00 x 102 mL x 100% = 10.0% (W/V) sodium chloride
  13. 13. Calculate Weight of Solute from6.2 Concentration Based on Weight/Volume Percent Calculate the number of grams of glucose in 7.50 x 102 mL of a 15.0% solution Mass W grams of solute % = × 100% V milliliters of solution 15.0% (W/V) = Xg glucose/7.50 x 102 mL x 100% Xg glucose x 100% = (15.0% W/V)(7.50 x 102 mL) Xg glucose = 113 g glucose
  14. 14. 6.2 Concentration Based on Weight/Weight Percent W grams solute % = ×100% W grams solutions • Weight/weight percent is most useful for Mass solutions of 2 solids whose masses are easily obtained • Calculate % (W/W) of platinum in gold ring with 14.00 g Au and 4.500 g Pt [4.500 g Pt / (4.500 g Pt + 14.00 g Au)] x 100% = 4.500 g / 18.50 g x 100% = 24.32% Pt
  15. 15. 6.3 Concentration of Solutions: Moles and Equivalents• Chemical equations represent the relative number of moles of reactants producing products• Many chemical reactions occur in solution where it is most useful to represent concentrations on a molar basis
  16. 16. 6.3 Moles and Equivalents Molarity • The most common mole-based concentration unit is molarity • Molarity – Symbolized M – Defined as the number of moles of solute per liter of solution moles solute M= L solution
  17. 17. 6.3 Moles and Equivalents Calculating Molarity from Moles • Calculate the molarity of 2.0 L of solution containing 5.0 mol NaOH • Use the equation moles solute M= L solution • Substitute into the equation: MNaOH = 5.0 mol solute 2.0 L solution = 2.5 M
  18. 18. 6.3 Moles and Equivalents Calculating Molarity From Mass • If 5.00 g glucose are dissolved in 1.00 x 102 mL of solution, calculate molarity, M, of the glucose solution • Convert from g glucose to moles glucose – Molar mass of glucose = 1.80 x 102 g/mol 5.00 g x 1 mol / 1.80 x 102 g = 2.78 x 10-2 mol glucose – Convert volume from mL to L 1.00 x 102 mL x 1 L / 103 mL = 1.00 x 10-1 L • Substitute into the equation: moles solute M= L solution Mglucose = 2.78 x 10-2 mol glucose 1.00 x 10-1 L solution = 2.78 x 10-1 M
  19. 19. 6.3 Moles and Equivalents Dilution Dilution is required to prepare a less concentrated solution from a more concentrated one – M1 = molarity of solution before dilution – M2 = molarity of solution after dilution – V1 = volume of solution before dilution – V2 = volume of solution after dilution moles solute M= moles solute = (M)(L solution) L solution
  20. 20. 6.3 Moles and Equivalents Dilution • In a dilution will the number of moles of solute change? – No, only fewer per unit volume • So, M1V1 = M2V2 • Knowing any three terms permits calculation of the fourth
  21. 21. 6.3 Moles and Equivalents Calculating Molarity After Dilution • Calculate the molarity of a solution made by diluting 0.050 L of 0.10 M HCl solution to a volume of 1.0 L – M1 = 0.10 M molarity of solution before dilution – M2 = X M molarity of solution after dilution – V1 = 0.050 L volume of solution before dilution – V2 = 1.0 L volume of solution after dilution • Use dilution expression M1V1 = M2V2 • X M = (0.10 M) (0.050 L) / (1.0 L) 0.0050 M HCl OR 5.0 x 10-3 M HCl
  22. 22. 6.3 Moles and Equivalents Representation of Concentration of Ions in Solution Two common ways of expressing concentration of ions in solution: 1. Moles per liter (molarity) • Molarity emphasizes the number of individual ions 2. Equivalents per liter (eq/L) • Emphasis on charge
  23. 23. 6.3 Moles and Equivalents Comparison of Molarity and Equivalents 1 M Na3PO4 • What would the concentration of PO43- ions be? • 1M • Equivalent is defined by the charge • One Equivalent of an ion is the number of grams of the ion corresponding to Avogadro’s number of electrical charges molar mass of ion (g) One equivalent of an ion = number of charges on ion
  24. 24. 6.3 Moles and Equivalents Molarity vs. Equivalents – 1 M Na3PO4 • 1 mol Na+ = 1 equivalent Na+ • 1 mol PO43- = 3 equivalents PO43- • Equivalents of Na+? – 3 mol Na+ = 3 equivalents of Na+ • Equivalents of PO43-? – 1 mol PO43- = 3 equivalents of PO43-
  25. 25. 6.3 Moles and Equivalents Calculating Ion Concentration • Calculate eq/L of phosphate ion, PO43- in a solution with 5.0 x 10-3 M phosphate • Need to use two conversion factors: – mol PO43- mol charge – mol charge eq PO43 5.0 x 10-3 mol PO43- x 3 mol charge x 1 eq 1L 1 mol PO43- 1mol charge • 1.5 x 10-2 eq PO43- /L
  26. 26. 6.4 Concentration-Dependent Solution Properties• Colligative properties - properties of solutions that depend on the concentration of the solute particles, rather than the identity of the solute• Four colligative properties of solutions 1. vapor pressure lowering 2. boiling point elevation 3. freezing point depression 4. osmotic pressure
  27. 27. 6.4 Concentration-Dependent Vapor Pressure of a Liquid Consider Raoult’s law in molecular Solution Properties terms • Vapor pressure of a solution results from escape of solvent molecules from liquid to gas phase • Partial pressure of gas phase solvent molecules increases until equilibrium vapor pressure is reached • Presence of solute molecules hinders escape of solvent molecules, lowering equilibrium vapor pressure
  28. 28. 6.4 Concentration-Dependent Vapor Pressure Lowering • Raoult’s law - when a nonvolatile solute is Solution Properties added to a solvent, vapor pressure of the solvent decreases in proportion to the concentration of the solute • Solute molecules (red below) serve as a barrier to the escape of solvent molecules resulting in a decrease in the vapor pressure
  29. 29. 6.4 Concentration-Dependent Freezing Point Depression and Solution Properties Boiling Point Elevation • Freezing point depression may be explained considering the equilibrium between solid and liquid states – Solute molecules interfere with the rate at which liquid water molecules associate to form the solid state • Boiling point elevation can be explained considering the definition as the temperature at which vapor pressure of the liquid equals the atmospheric pressure – If a solute is present, then the increase in boiling temperature is necessary to raise the vapor pressure to atmospheric temperature
  30. 30. 6.4 Concentration-Dependent Freezing Point Depression • Freezing point depression (∆Tf) - is proportional Solution Properties to the number of solute particles – Solute particles, not just solute • How does an electrolyte behave? – Dissociate into ions • An equal concentration of NaCl will affect the freezing point twice as much as glucose (a nonelectrolyte) • Each solvent has a unique freezing point depression constant or proportionality factor ∆Tf=kf m
  31. 31. 6.4 Concentration-Dependent Boiling point elevation • Boiling point elevation (∆Tb) - is Solution Properties proportional to the number of solute particles • An electrolyte will affect boiling point to a greater degree than a nonelectrolyte of the same concentration • Each solvent has a unique boiling point elevation constant ∆Tb=kb m
  32. 32. 6.4 Concentration-Dependent Osmotic Pressure • Some types of membranes appear impervious Solution Properties to matter, but actually have a network of small holes called pores • These pores may be large enough to permit small solvent molecules to move from one side of the membrane to the other • Solute molecules cannot cross the membrane as they are too large • Semipermeable membrane - allows solvent but not solute to diffuse from one side to another
  33. 33. 6.4 Concentration-Dependent Osmotic Pressure • Osmosis - the Solution Properties movement of solvent from a dilute solution to a more concentrated solution through a semipermeable membrane • Requires pressure to stop this flow
  34. 34. 6.4 Concentration-Dependent Osmotic Pressure Solution Properties • Osmotic pressure (π) - the amount of pressure required to stop the flow across a semipermeable membrane π=MRT • Osmolarity - the molarity of particles in solution – Osmol, used for osmotic pressure calculation
  35. 35. 6.4 Concentration-Dependent Tonicity and the Cell • Living cells contain aqueous solution and these cells Solution Properties are also surrounded by aqueous solution • Cell function requires maintenance of the same osmotic pressure inside and outside the cell • Solute concentration of fluid surrounding cells higher than inside results in a hypertonic solution causing water to flow into the surroundings, causing collapse = crenation • Solute concentration of fluid surrounding cells too low, results in a hypotonic solution causing water to flow into the cell, causing rupture = hemolysis • Isotonic solutions have identical osmotic pressures and no osmotic pressure difference across the cell membrane
  36. 36. 6.4 Concentration-Dependent Tonicity and the Cell Solution Properties Crenation Hemolysis Isotonic
  37. 37. 6.4 Concentration-Dependent Pickling Cucumber in Hypertonic Solution Properties Brine Due to Osmosis
  38. 38. 6.5 Water as a Solvent• Water is often referred to as the “universal solvent”• Excellent solvent for polar molecules• Most abundant liquid on earth• 60% of the human body is water – transports ions, nutrients, and waste into and out of cells – solvent for biochemical reactions in cells and digestive tract – reactant or product in some biochemical processes

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