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Mass Percentage, ppm, and ppb Definitions:

Ways of Expressing Concentration. Mass Percentage, ppm, and ppb Definitions:. Example: How would you prepare 425 g of an aqueous solution containing 2.40% by mass of sodium acetate, NaC 2 H 3 O 3 ?. Ans: Mass of NaC 2 H 3 O 3 = 10.2 g

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Mass Percentage, ppm, and ppb Definitions:

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  1. Ways of Expressing Concentration • Mass Percentage, ppm, and ppb • Definitions: Chapter 13

  2. Example: How would you prepare 425 g of an aqueous solution containing 2.40% by mass of sodium acetate, NaC2H3O3? Ans: Mass of NaC2H3O3 = 10.2 g Mass of H2O = mass of solution - mass of NaC2H3O3 = 415 g Chapter 13

  3. Exercise: Concentrated aqueous nitric acid has 69.0% by mass of HNO3 and has a density of 1.41 gcm-3. What volume of this solution contains 14.2 g of HNO3? Chapter 13

  4. Also mgl-1 Chapter 13

  5. Also μgl-1 Chapter 13

  6. Exercise: Seawater contains 0.0064 g of dissolved oxygen, O2, per litre. The density of seawater is 1.03 gcm-3. What is the concentration of oxygen, in ppm? Ans: 6.2 ppm Chapter 13

  7. Mole Fraction, Molarity, and Molality Chapter 13

  8. Converting between molarity (M) and molality (m) requires density. Exercise: 0.2 mol of ethylene glycol is dissolved in 2000 g of water. Calculate the molality Chapter 13

  9. Example: What is the molality of a solution containing 5.67 g of glucose, C6H12O6 (Mr = 180.2 g), dissolved in 25.2 g of water? (Calc. the mole fractions of the components as well). • Solution: • Think about the solute!................glucose (express in moles) • Think about the solvent!...............water (express in kilograms) Ans: 1.25 m Chapter 13

  10. Example: Converting molarity to molality An aqueous solution is 0.907 M Pb(NO3)2. What is the molality of lead nitrate, Pb(NO3)2, in this solution? The density of the solution is 1.252 g/mL. (Molar mass of Pb(NO3)2 = 331.2 g) Solution: • Mass of solution = density x volume • Calculate mass of Pb(NO3)2 , ie, moles x Mr • Mass of H2O = mass of solution – mass of Pb(NO3)2 • Molality = 0.953 m Pb(NO3)2 Chapter 13

  11. Colligative Properties • Colligative properties - depend only on the number of particles in solution and not on their identity. • So NaCl(aq) a +(aq) + Cl-(aq) • K2SO4(aq)  2K+(aq) + SO42-(aq) • C12H22O11(aq) C12H22O11(aq) Chapter 13

  12. Examining the effect of adding a non-volatile solute to a solvent on: • 1. vapor pressure • 2. boiling point • 3. freezing point • 4. osmosis Chapter 13

  13. Examples are: anti-freeze in the radiator water in a car prevents freezing in winter and boiling in summer; snow is melted by adding salt on sidewalks and streets Chapter 13

  14. Lowering Vapor Pressure • VP lowering depends on the amount of solute. Chapter 13

  15. Chapter 13

  16. Lowering Vapor Pressure • Raoult’s law: • Psoln = XsolventPosolvent • Recall Dalton’s Law: Ptotal = PA + PB + PC +….PN Chapter 13

  17. Ideal solution - obeys Raoult’s law • Raoult’s law is to solutions what the ideal gas law is to gases • Raoult’s law breaks down when the solvent-solvent and solute-solute intermolecular forces are greater than solute-solvent intermolecular forces • For liquid-liquid solutions where both components are volatile, a modified form of Raoult’s law applies: • Ptotal = PA + PB = XAPoA + XBPoB Chapter 13

  18. Example: Predict the vapour pressure of a solution prepared by mixing 35 g solid Na2SO4 (Mr = 142 g/mol) with 175 g water at 25oC. The vapour pressure of pure water at 25oC is 23.76 torr. Ans: 22.1 torr Chapter 13

  19. Exercise: The hydrocarbon limonene is the major constituent of lemon oil. A solution of limonene in 78.0 g of benzene had a vapour pressure of 90.6 mm Hg at 25oC, and the vapour pressure of pure benzene at 25oC is 95.2 mm Hg. What is its mass and molecular formula? Ans: C10H16 Chapter 13

  20. As with gases, ideal behaviour for solutions is never perfectly achieved • Nearly ideal behaviour is observed if solute-solute, solvent-solvent and solute-solvent interactions are very similar Chapter 13

  21. Boiling-Point Elevation • Goal: interpret the phase diagram for a solution. • Non-volatile solute lowers the vapor pressure • Therefore the triple point - critical point curve is lowered. Chapter 13

  22. Molal boiling-point-elevation constant, Kb, expresses how much Tb changes with molality, m: Chapter 13

  23. Freezing Point Depression Chapter 13

  24. Colligative Properties Freezing Point Depression Chapter 13

  25. Example: How many grams of ethanol, C2H5OH, must be added to 37.8 g of water to give a freezing point of -0.15oC? Solution: Water is the solvent and ethanol the solute From table 13.4, Tf = 0.15oC; Kf for water is 1.86oC/m Chapter 13

  26. Colligative properties of ionic solutions Tf = iKfm where i is the no. of ions resulting from each formula unit Chapter 13

  27. Example: Estimate the freezing point of a 0.010 m aqueous solution of aluminium sulphate, Al2(SO4)3. Assume the value of i based on the formula of the compound. Ans: -0.093oC Chapter 13

  28. Osmosis • Semipermeable membrane: permits passage of some components of a solution. Example: cell membranes and cellophane. • Osmosis: the movement of a solvent from low solute concentration to high solute concentration. Chapter 13

  29. Osmosis • Eventually the pressure difference between the arms stops osmosis. Chapter 13

  30. Osmosis • Osmotic pressure, , is the pressure required to stop osmosis: • Isotonic solutions are solutions….? Chapter 13

  31. Hypotonic solutions are solutions….? • Hypertonic solutions are solutions…? • Osmosis is spontaneous. • Red blood cells are surrounded by semipermeable membranes. Chapter 13

  32. Example: The formula for low-molecular weight starch is (C6H10O5)n, where n averages 2x102. When 0.798 g of starch is dissolved in 100 mL of water solution, what is the osmotic pressure at 25oC? • = 0.006 atm Chapter 13

  33. Exercise: Fish blood has an osmotic pressure equal to that of seawater. If seawater freezes at -2.3oC, what is the osmotic pressure of the blood at 25oC? Ans: 30 atm Chapter 13

  34. Crenation: • red blood cells placed in hypertonic solution (relative to intracellular solution); • The cell shrivels or swells up? Chapter 13

  35. Hemolysis: • there is a higher solute concentration in the cell; • What happens to the cell? Chapter 13

  36. Osmosis Chapter 13

  37. Hypertonic solution Hypotonic solution Chapter 13

  38. To prevent crenation or hemolysis, IV (intravenous) solutions must be isotonic. Chapter 13

  39. Cucumber placed in NaCl solution loses water to shrivel up and become a pickle. • Limp carrot placed in water becomes firm because water enters via osmosis. • Salty food causes retention of water and swelling of tissues (edema). • Water moves into plants through osmosis. • Salt added to meat or sugar to fruit prevents bacterial infection (a bacterium placed on the salt will lose water through osmosis and die). Chapter 13

  40. Active transport is the movement of nutrients and waste material through a biological system. • Active transport is not spontaneous. Chapter 13

  41. Colloids A colloid is a dispersion of particles of one substance (the dispersed phase) throughout another substance or solution (the continuous phase) Examples….?? Chapter 13

  42. The particle sizes range from ~1 x 103 pm to 2 x 105 pm in size Chapter 13

  43. Although a colloid appears to be homogeneous because the dispersed particles are quite small, it can be distinguished from a true solution by its ability to scatter light This is called the……effect? Chapter 13

  44. Left: vessel containing colloid; Right: true solution Chapter 13

  45. Aerosols – liquid droplets or solid particles dispersed in a gas e.g. fog and smoke Emulsion – liquid droplets dispersed throughout another liquid e.g. butterfat in milk Sol – solid particles dispersed in a liquid e.g. AgCl(s) in H2O Chapter 13

  46. Colloids in which the continuous phase in water can be hydrophilic (e.g. protein molecules) or hydrophobic colloids (Au particles in water). Chapter 13

  47. How does soap stabilise oil in water? And how do we digest fats in our digestive systems? Chapter 13

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