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I. PROPERTIES OF SOLUTIONS
- a homogeneous mixture - looks the same throughout Solubility: the amount of solute (dissolved substance) that dissolves in an of solvent (substance that does the dissolving) at a specific temperature Saturated: a solution containing the maximum amount of dissolved solute Unsaturated: a solution containing less than the maximum amount of dissolved solute
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Why would it be wrong to say that sugar and water are miscible?
describes liquids that DO dissolve in each other Ex. Water and vinegar Immiscible: describes liquids that DO NOT dissolve in each other Ex. Water and oil QUESTION: Why would it be wrong to say that sugar and water are miscible?
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Factors Affecting Solubility:
Temperature: Particle size: Pressure: **4. Agitation: - SOLIDS are MORE soluble in liquids at HIGHER temps. - GASES are LESS soluble in liquids at HIGHER temps. Why does warm soda go “flat?” Soda “goes flat” when the CO2 gas escapes from the liquid; At a warm temp. the CO2 gas is less soluble, so the gas escapes the liquid faster - SMALLER particles dissolve FASTER - GASES are MORE soluble in liquids at HIGHER pressures - Particles dissolve faster when stirred, mixed, shaken, etc.
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Solubility of compounds in 100g of H2O as a function of increasing temperature
Solubility of NaNO3 At 15°C? Solubility of KClO3 at 70°C? 85 g/ 100g H2O 30 g/ 100g H2O
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Use Figure 18.4 on pg. 504 to answer the following questions:
1.) What is the solubility of NH4Cl in water at 35°C? 2.) What is the solubility of NaNO3 in water at 10°C? 3.) What is the solubility of KBr in water at 65°C? 4.) What is the solubility of KNO3 in water at 70°C? 5.) Which compound’s solubility is relatively unaffected by increasing temperature? How do you know? 6.) Which compound’s solubility follows a trend opposite of the others? How do you know? 40 g / 100 g H2O 80 g / 100 g H2O 90 g / 100 g H2O 120 g / 100 g H2O NaCl, b/c its solubility curve remains relatively flat Yb2(SO4)3 ; its solubility decreases with increasing temp.
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Henry’s Law: Use to calculate: S1 x P2 = S2 x P1
The solubility of a gas in a liquid at different pressures S = solubility P = pressure Ex 1 : If the solubility of a gas in water is 0.77 g/L at 3.5 atm of pressure, what is its solubility at 1.0 atm? S1 = P1 = S2 = P2 = 0.77 g/L S1 x P2 = S2 x P1 3.5 atm ? 0.77 g/L x 1.0 atm = S2 3.5 atm S1 x P2 = S2 P1 1.0 atm 0.22 g/L= S2 Note: Pressure decreased so solubility decreased
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Ex 2: If the solubility of CO2 gas in water is 1.87 g/L at 10.5 atm of
pressure, what must the pressure be in order for the solubility to reach 2.56 g/L? S1 = P1 = S2 = P2 = 1.87 g/L S1 x P2 = S2 x P1 10.5 atm 2.56 g/L P2 = S2 x P1 S1 ? P2 = g/L x atm 1.87 g/L Note: Pressure had to increase for the solubility to increase P2 = atm
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Page 507: 1, 2 1: S1 x P2 = S2 x P1 (0.16 g/L) x (288 kPa) = S2 (104 kPa) S1 = P1 = S2 = P2 = 0.16 g/L 104 kPa 0.44 g/L= S2 ? S1 x P2 = S2 P1 Note: Pressure increased so solubility increased 288 kPa 2: S1 = P1 = S2 = P2 = 3.6 g/L S1 x P2 = S2 x P1 P2 = (9.5 g/L) x (1.0 atm) (3.6 g/L) 1.0 atm 9.5 g/L P2 = 2.64 atm P2 = S2 x P1 S1 ? Note: Solubility increased b/c pressure increased
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Page 508: Section Review 18.1 (3, 4, 6)
3. temperature, particle size, and pressure 4. By using Henry’s Law : S1 x P2 = S2 x P1 6. a. Add more solvent 6. b. Add more solute
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Practice: The solubility of CO2 in a can of soda is 4.2 g/L at 3.2 atm
of pressure. What is the solubility of the CO2 gas when the can of soda is opened and the pressure drops to 1.0 atm? What would happen to the solubility of the CO2 if the temperature went up and WHY? S1 x P2 = S2 x P1 (4.2 g/L) x (1.0 atm) = S2 (3.2 atm) S1 = P1 = S2 = P2 = 4.2 g/L 3.2 atm 1.3 g/L= S2 ? S1 x P2 = S2 P1 Note: Pressure decreased so solubility decreased 1.0 atm
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II. CONCENTRATIONS OF SOLUTIONS
a measure of the amount of solute dissolved in a given amount of solvent (a general term; no dependence on temp.) Dilute Solution: contains a small amount of solute Concentrated Solution: contains a large amount of solute Molarity (M): the unit for concentration Used to calculate: mol = M = L = M = mol L M x L mol M L mol L mol M
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Ex 1: What is the molarity of a solution containing 4.5 moles of KBr
in 3.0 L of solution? M= mol = L= ? 4.5 mol 3.0 L M = mol L M = 4.5 mol 3.0 L = 1.5 M or 1.5 mol/ L
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Ex 2: A saline solution contains 0.90 g of NaCl in exactly 100 mL of
solution. What is the molarity of the solution? M= mol = L= ? (this is what we solve for) ? (we get this from grams) 0.015 mol ? (we get this from mL) 0.100 L 1 mol NaCl 0.90 g NaCl x ________________ = mol NaCl 0.015 58.5 g NaCl (23.0) + (35.5) 100 mL = L (move the decimal 3 places left) = 0.15 M (or mol/L) M = mol L M = mol 0.100 L
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Ex 3: a.) How many moles of CaCl2 is needed to make 2.0 L of a 0.50 M
solution? b.) How many grams is this? M= mol = L= 0.50 M (mol/ L) ? (from moles, we can get the mass in grams) 2.0 L mol = M x L mol = (0.50 mol/L) x (2.0 L) mol mol = 1.0 mol CaCl2 M L (40.1) + (2 x 35.5) 111.1 111.1 g CaCl2 1.0 mol CaCl2 x ________________ = g CaCl2 1 mol CaCl2
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Page 511: M= mol = L= #9: ? 0.70 mol 0.250 L (250 mL = L) M = 2.8 mol/L M = mol L M = (0.70 mol) (0.250 L) #10: M= mol = L= 0.425 mol/L ? 0.335 L (335 mL = L) mol = M x L mol = (0.425 mol/L) x (0.335 L) mol = 0.14 mol NH4NO3
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#11: M= mol = L= 2.0 mol/L ? 0.250 L (250 mL = L) mol = M x L mol = (2.0 mol/L) x (0.250 L) mol = 0.50 mol CaCl2 55.6 111.1 g CaCl2 0.50 mol CaCl2 x ________________ = g CaCl2 1 mol CaCl2
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Page 515: #21a: M= mol = L= ? (this is what we solve for) ? (we get this from 400 grams) 2.5 mol 4.00 L 1 mol CuSO4 400 g CuSO4 x ________________ = mol CuSO4 2.5 159.6 g CuSO4 M = mol/L M = mol L M = (2.5 mol) (4.00 L)
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Page 515: #21b: M= mol = L= ? 0.06 mol 1.500 L (1500 mL = L) M = 0.04 mol/L M = mol L M = (0.06 mol) (1.500 L)
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Dilution Formula: Use to calculate:
M1 x V1 = M2 x V2 The molarity or volume of a solution made from another solution *Volume can be in L or mL. You don’t have to convert! Making Dilutions: moles of solution before dilution = moles of solution after dilution *There are no mole or gram conversions in these problems!! Ex 1: To prepare 100.L of M MgSO4, how many L of 0.200 M MgSO4 would you need? M1 = V1 = M2 = V2 = 0.400 M M1 x V1 = M2 x V2 (0.400 M) x (100. L) = V2 (0.200 M) 100. L 0.200 M M1 x V1 = V2 M2 ? 200 L= V2
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Ex 2: 500 mL of 2.5 M NaCl solution is diluted to 750 mL. What is
the new molarity of the solution? M1 = V1 = M2 = V2 = 2.5 M M1 x V1 = M2 x V2 (2.5 M) x (500 mL) = M2 (750 mL) 500 mL ? M1 x V1 = M2 V2 750 mL 1.7 M = M2
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Pg. 513: 12: 13: M1 = V1 = M2 = V2 = 0.760 M M1 x V1 = M2 x V2 (0.760 M) x (250.0 mL) = V2 (4.0 M) 250.0 mL 4.00 M M1 x V1 = V2 M2 ? 47.5 mL = V2 M1 = V1 = M2 = V2 = 0.20 M M1 x V1 = M2 x V2 (0.20 M) x (250 mL) = V2 (1.0 M) 250 mL 1.0 M M1 x V1 = V2 M2 ? 50 mL = V2
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Pg. 514: 14: ? = mL x 100 200 mL % v/v = Vol. solute (acetone) = Vol. solution = ? 10 mL 5 % 200.0 mL
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Percent by volume (%(v/v)):
Use to calculate: % v/v = Volume solute x 100 Volume solution %v/v or vol. of solute Ex 1: What is the percent by volume of a solution of rubbing alcohol that contains 25.0 mL of alcohol in 85.0 mL of solution? % v/v = Vol. solute (alcohol) = Vol. solution = ? 85.0 mL 25.0 mL alcohol 25.0 mL 85.0 mL % v/v = mL x 100 85.0 mL = 29.4%
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Ex 2: A bottle of hydrogen peroxide (H2O2) antiseptic is labeled 3.0%
H2O2 by volume. How many mL of H2O2 are in a 400 mL bottle of this solution? % v/v = Vol. solute (H2O2) = Vol. solution = 3.0 % ? 3.0 % = ? x 100 400 mL 400 mL (400 mL ) x (3.0 %) = ? 100 12 mL H2O2 400 mL 388 mL H2O 12 mL = vol. H2O2
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Because volume depends on temperature and molarity depends on
IV. CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES Because volume depends on temperature and molarity depends on Volume, we need a way of expressing solution concentration when Temperature changes. To do that, we use molality: m = mol solute kg solvent Molality (m): Although we could use this formula to solve for m, mol, or kg, we will focus on using it only to find molality (m)
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Ex : Calculate the molality of a solution prepared by dissolving
7.5 mol LiCl in 2.1 kg of H2O. Solute = LiCl Solvent = H2O m = mol = kg = ? (this is what we solve for) 7.5 mol 2.1 kg m = mol kg m = 7.5 mol 2.1 kg = 3.6 mol/kg
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Ex : What is the molality of a solution containing 10.0 g NaCl
dissolved in 600. g of H2O? Solute = NaCl Solvent = H2O m = mol = kg = ? (this is what we solve for) ? (we get this from g NaCl) 0.17 mol ? (we get this from g H2O) 0.600 kg 1 mol NaCl 10.0 g NaCl x ________________ = mol NaCl 0.17 58.5 g NaCl 600. g = kg (move the decimal 3 places left) = 0.28 mol/kg m = mol kg m = 0.17 mol 0.600 kg
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III. COLLIGATIVE PROPERTIES OF SOLUTIONS
depend only on the number of particles dissolved in a solution NOT on what they are → Remember, only IONIC compounds (metal & nonmetal) break apart in H2O, MOLECULAR do NOT Ex. How many particles are released when each compound dissolves in water? NaCl CaF MgO LiBr K2S 2 3 2 2 3
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Boiling Point Elevation:
the increase in temperature between the boiling point of a solution & the boiling point of a pure solvent Ex. Salt water boils ABOVE 100°C Freezing Point Depression: the decrease in temperature between the freezing point of a solution & the freezing point of a pure solvent Ex. Salt water freezes BELOW 0°C
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∆Tb = Kb x m x n ● Boiling Point Elevation: ∆Tb : Kb : m: n: change in boiling temp. Constant for the solvent molality # ions in solution ** If the solution contains an IONIC solid ( ______ & _____), you must multiply the molality of the solution by the number of ions in solution M NM Ex. NaCl (aq) → Na+ (aq) + Cl- (aq) ____ ions, so n = MgCl2 (aq) → Mg2+ (aq) Cl-(aq) ____ ions, so n =
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Ex 1: What is the boiling point of an aqueous 1.50 m NaCl solution?
Kb for H2O = 0.512°C/m. ∆Tb = Kb x m x n ∆Tb = Kb = m = n = ? 0.512 °C/m 1.50 m 2 (Na+ and Cl-) ∆Tb = (0.512 °C/m) x (1.50 m) x (2) ∆Tb = 1.5°C New boiling pt = Original b.p. of solvent + ΔTb New boiling pt = 100°C °C = 101.5°C
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Ex 2: What is the boiling point of a solution that contains 1.25 mol
CaCl2 in 1.4 kg of H2O? Kb for H2O = 0.512°C/m ∆Tb = Kb x m x n ∆Tb = Kb = m = n = ? 0.512 °C/m 1.25 mol CaCl2 1.4 kg H2O = 0.89 m 3 (Ca2+ and 2 Cl-) ∆Tb = (0.512 °C/m) x (0.89 m) x (3) ∆Tb = 1.4°C New boiling pt = Original b.p. of solvent + ΔTb New boiling pt = 100°C °C = 101.4°C
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● Freezing Point Depression:
∆Tf = Kf x m x n ∆Tf : Kf : m: n: change in freezing temp. Constant for the solvent molality # ions in solution ** These problems are solved the same way as boiling point elevation problems except Kf is used and the ∆T tells you how much the temperature goes down
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Ex 1: What is the freezing point of a 0.20 m aqueous K2SO4
solution? Kf for H2O = 1.86°C/m. ∆Tf = Kf x m x n ∆Tf = Kf = m = n = ? 1.86 °C/m 0.20 m 3 (2 K+ and 1 SO42-) ∆Tf = (1.86 °C/m) x (0.20 m) x (3) ∆Tf = 1.1°C New freezing pt = Original f.p. of solvent - ΔTf New freezing pt = 0.0°C °C = - 1.1°C
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Ex 2: An aqueous solution of glucose (C6H12O6) in water has a
concentration of 0.45 m. What is the freezing point of the solution? Kf for H2O = 1.86°C/m. ∆Tf = Kf x m x n ∆Tf = Kf = m = n = ? 1.86 °C/m 0.45m 1 (glucose is NOT ionic!) ∆Tf = (1.86 °C/m) x (0.45 m) x (1) ∆Tf = 0.8°C New freezing pt = Original f.p. of solvent - ΔTf New freezing pt = 0.0°C °C = - 0.8°C
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Ex 1: What is the freezing point of a solution in which 12.0 mol CCl4
is dissolved in 75.0 kg C6H6? Kf (°C/m) for C6H6 is 5.12 and the freezing point is 5.5˚C. ∆Tf = Kf x m x n ∆Tf = Kf = m = n = ? 5.12 °C/m 12.0 mol CCl4 75.0 kg C6H6 = 0.16 m 1 (CCl4 is not ionic so it doesn’t break apart in water) ∆Tf = (5.12 °C/m) x (0.16 m) x (1) ∆Tb = 0.8°C New freezing pt = Original f.p. of solvent - ΔT New freezing pt = 5.5°C °C = 4.7°C
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Pg. 528: 55.a. What is the boiling point of a solution that contains: 0.50 mol glucose (molecular) in 1000 g of H2O? (Kb (°C/m) for H2O is ) ∆Tb = Kb x m x n ∆Tb = Kb = m = n = ? 0.512 °C/m 0.50 mol glucose 1.000 g H2O = 0.50 m 1 (b/c glucose is not ionic, its doesn’t break apart) ∆Tb = (0.512 °C/m) x (0.50 m) x (1) ∆Tb = 0.3°C New boiling pt = Original b.p. of solvent + ΔT New boiling pt = 100°C °C = 100.3°C
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Pg. 528: 55.a. What is the boiling point of a solution that contains: 1.50 mol NaCl in 1000 g of H2O? (Kb (°C/m) for H2O is ) ∆Tb = Kb x m x n ∆Tb = Kb = m = n = ? 0.512 °C/m 1.50 mol NaCl 1.000 g H2O = 1.50 m 2 (Na+ and Cl-) ∆Tb = (0.512 °C/m) x (1.50 m) x (2) ∆Tb = 1.5°C New boiling pt = Original b.p. of solvent + ΔT New boiling pt = 100°C °C = 101.5°C
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Ex : Calculate the molality of a solution prepared by dissolving
24.5 g NaCl in 2.5 kg of H2O. Solute = NaCl Solvent = H2O m = mol = kg = ? (this is what we solve for) ? (we get this from grams NaCl) 0.42 mol 2.5 kg 1 mol NaCl 24.5 g NaCl x ________________ = mol NaCl 0.42 58.5 g NaCl = 0.17 mol/kg m = mol kg m = 0.42 mol 2.5 kg
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Ex : How many moles of KBr must be dissolved in 2.0 kg of water to
form a 3.1 m solution? Solute = KBr Solvent = H2O m = mol = kg = 3.1 mol/ kg ? 2.0 kg mol = m x kg mol = 3.1 mol x 2.0 kg kg mol m kg = 6.2 mol
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Ex : How many grams of LiF must be dissolved in 4.5 kg of water to
form a 2.8 m solution? Solute = LiF Solvent = H2O m = mol = kg = 2.8 mol/ kg ? (from moles, we can find grams) 4.5 kg mol = m x kg mol = 2.8 mol x 4.5 kg kg = 12.6 mol mol m kg 25.9 g LiF 12.6 mol LiF x _____________ = g LiF 326.3 1 mol LiF
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