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Characteristics and Mechanisms of Solutions: A Comprehensive Guide

Explore the characteristics of solutions, including homogeneous mixtures and solubility, as well as the mechanisms of dissolving. Learn about solvation, factors that affect the rate of dissolving, and the concept of solubility. Discover the concentration of solutions through molarity and percent solutions. Dive into the colligative properties of solutions, such as vapor pressure, boiling point elevation, and freezing point depression. Understand the concept of mole fraction and its relevance to electrolytes.

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Characteristics and Mechanisms of Solutions: A Comprehensive Guide

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  1. Chapter 18 Solutions

  2. I. Solutions A. Characteristics of solutions 1. Homogeneous mixture 2. Contains a solute and solvent 3. Can be a gas, liquid or solid 4. Soluble - able to dissolve 5. Insoluble - not able to dissolve

  3. 6. Miscible - 2 liquids able to mix 7. Immiscible - 2 liquids not able to mix B. Dissolving mechanisms 1. Solute-solute attraction is broken up, requiring energy

  4. 2. Solvent-solvent attraction is broken up, requiring energy 3. Solute-solvent attraction is formed, releasing energy

  5. C. Solvation 1. When solvent particles surround solute particles to form a solution 2. Depends on polarity and bonding

  6. D. Factors that affect rate of dissolving 1. Agitating the mixture 2. Increase surface area 3. Increase temperature 4. Heat of solution (exothermic or endothermic reactions)

  7. E. Solubility 1. Ability to dissolve 2. Saturated solutions - maximum amount of solute that can dissolve 3. Unsaturated solutions - less solute than a saturated solution

  8. 4. Supersaturated solution - has more solute than a saturated solution at the same temperature a. Formed at higher temp b. Cooled slowly 5. As temperature is increased solids dissolve faster

  9. 6. Lower temp. gases dissolve better 7. Pressure affects gases not solids F. Henry’s Law 1. At a given temp. the solubility (s) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid

  10. 2. S1 = S2 P1 P2 units = g/L 3. Ex. If 0.24 g of a gas dissolves in 1.0 L of water at 1.5 atm pressure, how much gas will dissolve if the pressure is raised to 6.0 atm? T remains constant.

  11. Concentration of Solutions A. Molarity 1. Concentration: amount of solute that is dissolved in a given quantity of solvent a. Dilute solution: contains a small amount of solute, large amounts of solvent

  12. b. concentrated solution: Contains a small amount of solvent and a large amount of solute 2. Molarity (M) a. Way to express concentration b. Number of moles of solute in liters of solution

  13. c. M = moles of solute Liters of solution d. Example: What is the molarity of an aqueous solution that contains 14.2 gNaCl dissolved in 2364 mL of the solution?

  14. B. Making dilutions 1. Moles of solute before dilution = moles of solute after dilution 2. M1V1 = M2V2 3. Example: How many milliters of a stock solution of 2.00 M MgSO4 would you need to prepare 100.0 mL of 0.400 M MgSO4?

  15. C. Percent Solutions Mass of solute (g) Solution volume (mL) 1. % mass/ volume X 100 = a. Ex. What is the percent by mass of sodium carbonate in a water solution containing 0.497 g NaCO3 in 58.3 g of solution?

  16. b. The % mass of MgCl2 in a water solution is 1.47%. How many g of solute are dissolved in each 500.00 g of solution? Volume of solute Solution volume 2. % volume = X 100

  17. a. Ex. What is the %v/v of ethanol (C2H6O) in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with water?

  18. Colligative Properites A. Definition: Properties that depend only on the number of particels dissolved in a given mass of solvent

  19. B. Vapor pressure 1. A vapor that is dynamic equilibrium with its liquid in a closed system 2. Dynamic equilibrium: when the forward and the reverse reactions are equal

  20. 3. If it contians nonvolatile solutes (does not dissociate) 4. If it contains ionic compounds it dissociates completely.

  21. C. Boiling point – the temperature difference between a solutions boiling point and a pure solvent’s boiling point D. ΔTb (boiling point elevation) – directly proportional to molality

  22. E. molality 1. moles of solute per kg of solution 2. m = moles of solute kg of solution

  23. F . For nonelectrolyte(does’t dissociate) 1. ΔTb = Kbm Kb – molal boiling point elevation constant units  oC/m m- molality 2. 1 m or .512 oC .512 oC 1 m for when water is the solvent

  24. 3. What is the boiling point elevation when 31.5 g of methanol (C10H20O) is dissolved in 258 g of acetic acid? Kb for acetic acid is 2.93 oC/m.

  25. 4. How many grams of styrene glycol (C8H10O2) must be dissolved in 98.7g of bezene to raise the boiling point by 8.57 oC?Kb for benzene is 2.67oC/m.

  26. G. Freezing point depression (ΔTf) 1. The temperature difference between the freezing point of a solution and the freezing point of its pure solvent. 2. For nonelectrolytes ΔTf = Kfm

  27. 3. When water is the solvent Kf = 1.86 oC/m 4. Calculate the freezing point of a solution containing 5.70 g of sugar(C12H22O11) in 50.0 g of water.

  28. 5. If 13.4g of the medication scopolamine, C17H21NO4, is dissolved in 50.3 g of water, how much will the freezing point be lowered?

  29. IV. Molar fraction and Electrolytes A. Mole fraction 1. The ratio of the moles of solute in solution to the total number of moles of both solvent and solute

  30. 2. Mole expressions a. XA = nA nA + nB (for solute) b. XB = nB nA + nB (for solvent)

  31. 3. Ex. Compute the mole fraction of each component in a solution of 1.25 mole of ethylene glycol (EG) and 4.00 mole water.

  32. B. Boiling point elevations ∆Tb = (# particles)(Kb)(m) C. Freezing point depression ∆Tf = (# particles)(Kf)(m)

  33. D. Molar mass 1. boiling point elevation m = ∆Tb Kb 2. freezing point depression m = ∆Tf Kf

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