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Published byAldous Blankenship Modified over 9 years ago
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Chapter 18 Solutions
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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
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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
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2. Solvent-solvent attraction is broken up, requiring energy 3. Solute-solvent attraction is formed, releasing energy
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C. Solvation 1. When solvent particles surround solute particles to form a solution 2. Depends on polarity and bonding
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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)
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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
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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
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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
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2. S 1 = S 2 P 1 P 2 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.
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II.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
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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
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B. Making dilutions 1. Moles of solute before dilution = moles of solute after dilution 2. M 1 V 1 = M 2 V 2 3. Example: How many milliters of a stock solution of 2.00 M MgSO 4 would you need to prepare 100.0 mL of 0.400 M MgSO 4 ?
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a. Ex. What is the percent by mass of sodium carbonate in a water solution containing 0.497 g NaCO 3 in 58.3 g of solution? C. Percent Solutions
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b. The % mass of MgCl 2 in a water solution is 1.47%. How many g of solute are dissolved in each 500.00 g of solution?
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a. Ex. What is the %v/v of ethanol (C 2 H 6 O) in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with water?
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III.Colligative Properites A. Definition: Properties that depend only on the number of particels dissolved in a given mass of solvent
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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
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3. If it contians nonvolatile solutes (does not dissociate) 4. If it contains ionic compounds it dissociates completely.
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C. Boiling point – the temperature difference between a solutions boiling point and a pure solvent’s boiling point D. ΔT b (boiling point elevation) – directly proportional to molality
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E. molality 1. moles of solute per kg of solution 2. m = moles of solute kg of solution
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F. For nonelectrolyte(does’t dissociate) 1. ΔT b = K b m K b – molal boiling point elevation constant units o C/m m- molality 2. 1 m or.512 o C.512 o C 1 m for when water is the solvent
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3. What is the boiling point elevation when 31.5 g of methanol (C 10 H 20 O) is dissolved in 258 g of acetic acid? K b for acetic acid is 2.93 o C/m.
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4. How many grams of styrene glycol (C 8 H 10 O 2 ) must be dissolved in 98.7g of bezene to raise the boiling point by 8.57 o C?K b for benzene is 2.67 o C/m.
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G. Freezing point depression (ΔT f ) 1. The temperature difference between the freezing point of a solution and the freezing point of its pure solvent. 2. For nonelectrolytes ΔT f = K f m
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3. When water is the solvent K f = 1.86 o C/m 4. Calculate the freezing point of a solution containing 5.70 g of sugar(C 12 H 22 O 11 ) in 50.0 g of water.
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5. If 13.4g of the medication scopolamine, C 17 H 21 NO 4, is dissolved in 50.3 g of water, how much will the freezing point be lowered?
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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
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2. Mole expressions a. X A = n A n A + n B (for solute) b. X B = n B n A + n B (for solvent)
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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.
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B. Boiling point elevations ∆T b = (# particles)(K b )(m) C. Freezing point depression ∆T f = (# particles)(K f )(m)
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D. Molar mass 1. boiling point elevation m = ∆T b K b 2. freezing point depression m = ∆T f K f
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