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Chapter 15 Solutions

Chapter 15 Solutions . Like Dissolves Like. Definitions. Solution - homogeneous mixture. Solute - substance being dissolved. Solvent - present in greater amount. Solvation. Solvation the process of dissolving. solute particles are surrounded by solvent particles. First.

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Chapter 15 Solutions

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  1. Chapter 15Solutions Like Dissolves Like

  2. Definitions • Solution - homogeneous mixture Solute - substance being dissolved Solvent - present in greater amount

  3. Solvation • Solvation • the process of dissolving solute particles are surrounded by solvent particles First... solute particles are separated and pulled into solution Then...

  4. Solvation • Dissociation • separation of an ionic solid into aqueous ions • movie NaCl(s)  Na+(aq) + Cl–(aq)

  5. Solvation • Molecular Solvation • molecules stay intact C6H12O6(s)  C6H12O6(aq)

  6. Solvation • Ionization • breaking apart of some polar molecules into aqueous ions HNO3(aq) + H2O(l)  H3O+(aq) + NO3–(aq)

  7. - + - - + + acetic acid salt sugar Solvation Non- Electrolyte Weak Electrolyte Strong Electrolyte solute exists as ions and molecules solute exists as molecules only solute exists as ions only

  8. Making solutions • In order to dissolve, the solvent molecules must come in contact with the solute. • Stirring moves fresh solvent next to the solute. • The solvent touches the surface of the solute. • Smaller pieces increase the amount of surface area of the solute.

  9. Solution Formation • Nature of the solute and the solvent • Whether a substance will dissolve • How much will dissolve • Factors determining rate of solution... • stirred or shaken (agitation) • particles are made smaller • temperature is increased • Why?

  10. Temperature and Solutions • Higher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often. • Speeds up dissolving. • Usually increases the amount that will dissolve (exception is gases)

  11. How Much? • Solubility- The maximum amount of substance that will dissolve at a specific temperature (g solute/100 g solvent) • Saturated solution- Contains the maximum amount of solute dissolved. movie • Unsaturated solution- Can still dissolve more solute • Supersaturated- solution that is holding more than it theoretically can; seed crystal will make it come out. movie

  12. UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form Solubility concentration

  13. Cloud Seeding • Ever heard of seeding the clouds to make them produce rain? • Clouds- mass of air supersaturated with water vapor • Silver Iodide (AgI) crystals are dusted into the cloud • The AgI attracts the water, forming droplets to attract others

  14. Liquids • Miscible means that two liquids can dissolve in each other • water and antifreeze, water and ethanol • Partially miscible- slightly dissolve • Immiscible can’t mix • oil and vinegar

  15. NONPOLAR NONPOLAR POLAR POLAR Solvation • Detergents • polar “head” with long nonpolar “tail” • can dissolve nonpolar grease in polar water “Like Dissolves Like”

  16. Solubility? • For solids in liquids, as the temperature goes up-the solubility usually goes up. • For gases in a liquid, as the temperature goes up-the solubility goes down. • For gases in a liquid, as the pressure goes up-the solubility goes up.

  17. Mentos and Diet Coke • Solubility can also be affected by other factors such as a reduction in water surface tension and the formation of nucleation sites. Nucleation sites are places where gas molecules gather to form a bubble. Mentos contains compounds that reduce surface tension and at the same time the rough surface of the dissolving tablet provides nucleation sites. The combination in rather dramatic as evidenced in the video clip.

  18. Solubility • Solubility • maximum grams of solute that will dissolve in 100 g of solvent at a given temperature • varies with temp • based on a saturated solution

  19. Solubility • Solubility Curve • shows the dependence of solubility on temperature

  20. Solubility • Solids are more soluble at... • high temperatures. • Gases are more soluble at... • low temperatures. • high pressures (Henry’s Law). • EX: nitrogen narcosis, the “bends,” soda

  21. The Bends Shallow Water Blackout DVD Movie

  22. = Gases in liquids... • Henry’s Law - says the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid • think of a bottle of soda pop, removing the lid releases pres. • Equation: S1 S2 P1 P2

  23. Henry’s Law Example

  24. Concentration is... • a measure of the amount of solute dissolved in a given quantity of solvent • Aconcentrated solution has a large amount of solute • Adilute solution has a small amount of solute • thus, only qualitative descriptions • But, there are ways to express solution concentration quantitatively

  25. Concentration • The amount of solute in a solution. • Describing Concentration • % by mass - medicated creams • % by volume - rubbing alcohol • ppm, ppb - water contaminants • molarity - used by chemists • molality - used by chemists

  26. Molarity - Most Important • The number of moles of solute in 1 Liter of the solution. Note: not solvent. • M = moles/Liter; such as 6.0 molar • What is the molarity of a solution with 2.0 moles of NaCl in 250 mL of solution?

  27. Dilution Adding water to a solution

  28. Dilution • Preparation of a desired solution by adding water to a concentrate. • Moles of solute remain the same.

  29. Dilution • The number of moles of solute doesn’t change if you add more solvent! • The # moles before = the # moles after • Since M x L = moles then • M1 x V1 = M2 x V2 • M1 and V1 are the starting concentration and volume. • M2 and V2 are the final concentration and volume. • Stock solutions are pre-made to a known Molarity

  30. Dilution • What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution? GIVEN: M1 = 15.8M V1 = ? M2 = 6.0M V2 = 250 mL WORK: M1 V1 = M2 V2 (15.8M)V1 = (6.0M)(250mL) V1 = 95 mL of 15.8M HNO3

  31. 95 mL of15.8M HNO3 250 mL mark water for safety Preparing Solutions • 250 mL of 6.0M HNO3by dilution • measure 95 mL of 15.8M HNO3 • combine with water until total volume is 250 mL • Safety: “Do as you oughtta, add the acid to the watta!”

  32. Making Solutions • Pour in a small amount of solvent • Then add the solute (to dissolve it) • Carefully fill to final volume. • Also remember: M x L = moles of solute • How many moles of NaCl are needed to make 8.0 L of a 0.75 M NaCl solution?

  33. Practice • 2.0 L of a 0.88 M solution are diluted to 3.8 L. What is the new molarity? • You have 150 mL of 6.0 M HCl. What volume of 1.3 M HCl can you make? • You need 450 mL of 0.15 M NaOH. All you have available is a 2.0 M stock solution of NaOH. How do you make the required solution?

  34. Making Solutions • 10.3 g of NaCl are dissolved in a small amount of water, then diluted to 250 mL. What is the concentration? • How many grams of sugar are needed to make 125 mL of a 0.50 M C6H12O6 solution?

  35. Percent Solutions... • Percent means parts per 100, so • Percent by volume: = Volume of solute x 100 Volume of solution • indicated %(v/v) • What is the percent solution if 25 mL of CH3OH is diluted to 150 mL with water?

  36. Percent Solutions • Percent by mass: = Mass of solute(g) x 100 Mass of solution(g) • Indicated %(m/m) • More commonly used • 4.8 g of NaCl are dissolved in 82 g of solution. What is the percent of the solution?

  37. Colligative Properties Depend only on the number of dissolved particles Not on what kind of particle

  38. Colligative Applications • Common Applications • salting icy roads • making ice cream • antifreeze • cars (-64°C to 136°C) • fish

  39. Boiling Point Elevation Solute particles weaken IMF in the solvent.

  40. Boiling Point Elevation • The vapor pressure determines the boiling point. • Lower vapor pressure = higher boiling point. • Salt water boils above 100ºC • The number of dissolved particles determines how much, as well as the solvent itself.

  41. Depends on # of Pieces • Electrolytes form ions when they are dissolved = more pieces. • NaCl ® Na+ + Cl- (= 2 pieces) • More pieces = bigger effect

  42. Vapor Pressure Decreased • The bonds between molecules keep molecules from escaping. • In a solution, some of the solvent is busy keeping the solute dissolved. • Lowers the vapor pressure

  43. Freezing Point Depression • Solids form when molecules make an orderly pattern. • The solute molecules break up the orderly pattern. • Makes the freezing point lower. • Salt water freezes below 0ºC • How much depends on the number of solute particles dissolved.

  44. Freezing Point Depression

  45. Properties of Water • Ice is less dense than water • movie

  46. mass of solvent only 1 kg water = 1 L water Molality

  47. Molality • a new unit for concentration • m = Moles of solute kilogram of solvent • m = Moles of solute 1000 g of solvent • What is the molality of a solution with 9.3 mole of NaCl in 450 g of water?

  48. Molality • Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.250 kg water = 3.2m MgCl2

  49. Molality • How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water? 0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

  50. 500 mL of 1.54M NaCl 500 mLwater 500 mL volumetric flask 500 mL mark 45.0 gNaCl Preparing Solutions • 1.54m NaCl in 0.500 kg of water • mass 45.0 g of NaCl • add water until total volume is 500 mL • mass 45.0 g of NaCl • add 0.500 kg of water

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