chapter 8 solutions
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Chapter 8 Solutions
A. Definition
• A solution is a homogeneous mixture of two or more different substances • only one phase• composition is variable• almost always clear (transparent)• A solution cannot be separated into its components by filtration
Solute – dissolved substance (smaller amount)Solvent – dissolving medium (larger amount)
Solutions can be in gas, liquid or solid phases
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B. Types of solutions a) Solid – liquid
1. Ionic compoundNaCl in water NaCl Na+ + Cl- breaking of ionic bond
H2O
Hydration
Ion-dipole attraction
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2. Covalent compounds
sugar in water
O OH
OH
OH
HO
HOH2C
H
O
H
H
O
H
H
O
H
HO
H 3
b. Liquid - liquid
C O H and H2O
H
H
H
(CH3OH)
Polar polar
H O
CH3
H O
H
H O
CH3
Polar dissolves in polarNonpolar dissolves in nopolar
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c. Gas – liquid All gases are slightly soluble in water
d. Gas-gas All mixtures of gases are solutions
e. Solid – solidCu (copper) in Au (gold) Alloy
Brass (Cu/Zn)
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C. SolubilitySoluble – dissolves a large amountInsoluble – dissolves an negligible amount
Miscible – both components are liquid and can dissolve (mix) in any proportion
example: H2O and CH3OH
a) Solubility - # of grams that can be dissolved in 100 g of solvent at saturation (equilibrium)
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Figure 8.3 In a saturated solution, the dissolved solute is in equilibrium with the undissolved solute.
Example:7
Table 8.1 Solubilities of Various Compounds in Water at 0oC, 50oC, and 100oC.
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Unsaturated solution – dissolved amount less than solubility
Supersaturated solution - dissolved amount more than
solubilityAqueous solution – solution in water
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D. Factors affecting solubility 1. Nature of solute and solvent
In general, for non-ionic solutes, “like dissolves like’.
• polar solutes dissolve in polar solvents. • nonpolar solutes dissolve in nonpolar solvents.
Ionic compounds do not dissolve in nonpolar solvents
CH4 in water? NaCl in octane (nonploar)?
CH4OH in water?
HCl in water?
Examples
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Solubility Guidelines for common Ionic Compounds in Water.
1. All compounds containing group IA (Li+, Na+, K+, etc.) and NH4
+ are soluble in water.
2. All nitrates (NO3-) and acetates (CH3COO- or C2H3O-)
are soluble in water.
3. All chlorides (Cl-), bromides (Br-) and iodides (I-) are soluble in water except those of Ag+, Pb2+ and Hg2
2+.
4. All sulfates (SO42-) are soluble except
PbSO4, BaSO4, SrSO4 and CaSO4
5. All hydroxides (OH-) are insoluble except those of IA & Ca(OH)2, Sr(OH)2, Ba(OH)2
6. Most other ionic compounds are insoluble in water11
Li+, Na+, K+ and NH4+ soluble
NO3-, CH3COO- soluble
Cl- , Br-, I- soluble AgX, PbX2, Hg2X2.SO4
2- soluble PbSO4, BaSO4,CaSO4, SrSO4
OH- insoluble IA, Ca2+, Sr2+, Ba2+
Solubility except
K2SO4
NaCl
PbCl2
MgSO4
Soluble in water?
CaCO3
Fe(NO3)2
NH4MnO4
Soluble in water?
BaSO4
CuCr2O7
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Which of the following would be expected to be the most soluble in water?
C C C
H
H
H
H
H
H
H
H
C C C
H
H
H
H
H
H
O
H
C C C
H
H
H
H
H
H
C
H
O
H
H
H
H
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2. TemperatureGenerally, solubility increases as T increases, except for most gases in liquid where solubility decreases as T increases.
Example: O2 in water
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3. Pressure (above the surface of the solution) Only affects solubility of gases in liquid.
Solubility increase as P increases.
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E. Concentrations of solutions - amount of solute in certain amount of solvent or solution.
a) % by mass (mass-mass %)
b) % by volume (V-V %)
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Figure 8.7 When volumes of two different liquids are combined, the volumes are not additive.
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Figure 8.8
Identical volumetric flasks are filled to the 50.0-mL mark with ethanol and
with water.
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c) mass-volume %
d) parts per million (ppm)
e) parts per billion (ppb)
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If an aqueous solution is 2.5 % w/v in aluminum sulfate, Al2(SO4)3, how many grams of aluminum sulfate are there in a liter of solution?
Examples
How many grams of zinc fluoride, ZnF2, are required to make a 5.00 % w/v aqueous solution in a 250 mL volumetric flask?
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e) Molarity, M (molar concentration)
# of moles of solute/liters of solution
Example 10.50 mol KOH is dissolved in 2.0L of solution. Find the molarity.
1L
NaCl
1 mole NaCl
1 M NaClsolution
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Example 2How many grams of NaCl is needed to make 250 mL of a 0.50 M NaCl solution?
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Example 3. Make a 500mL of 0.250 M K2Cr2O7 solution
MW of K2Cr2O7 = 294.2
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F. Dilution
)(literV
nM or MV = n
In general, C1V1 = C2V2, where C stands for concentration
M1V1 = M2V2
M2V2
M1V1
addwater
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M1V1 = M2V2
Example 1. A 250 mL 2.0M NaOH solution is diluted to 1.0 L. What is the molarity of the final solution?
Example 2. What volume of a 5.0M HCl solution would be needed to prepare 2.0 L of a 0.25M HCl solution?
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G. Colligative properties of solutions
A colligative property is a physical property of a solutionthat depends only on the concentration.
a) Lowering of vapor pressure
water
Next day
sugar in water
water
sugar in water
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water
sugar in water
b) Elevation of the Boiling point
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c) Freezing point (depression) lowering
Example: Antifreeze; salt-water.
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H2O solution
Semi-permeable membrane
d) Osmosis and Osmotic pressure
Osmosis: the flow of solvent through a semipermeable membrane from a dilute to a more concentrated solution.At equilibrium, the molecules move back and forth at equal rates.
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H2O solution
This measures the osmoticpressure of the solution
The process is called osmosisPressure applied to prevent osmosis = osmotic pressure
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Copyright © Houghton Mifflin Company. All rights reserved. 8–15
Figure 8.15Osmotic pressure is the amount of pressure needed to prevent the solution in the tube from rising as a result of the process of osmosis.
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V.P. lowering, B.P. elevation and F.P depression and osmotic pressure depend on the concentration of the solute particles but not on the type of solute.
Examples:
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Example:
1.5 mol of K2CrO4 is dissolved in 1000 g of water. What is the freezing point of the solution?
Freezing point (depression) lowering
mol of particle =
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Osmolarity
NaCl Na+ + Cl-
1M NaCl 2 mol ions osmolarity = 2M
osmolarity = M x i
i = # of particles produced from the dissociation of one formula unit of solute
H2O
Osmolarity in cell = 0.31M (osmol)Osmolarity = 0.31M isotonic solution 5.0% m/v glucose 0.92% m/v NaCl (physiological saline solution) 35
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Osmolarity = 0.31M isotonic solution
Osmolarity > 0.31M hypertonic solution
Osmolarity < 0.31M hypotonic solution
cell
crenation
Burst(hemolysis)
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Red blood cell in
a) isotonic solution b) Hypertonic solution c) Hypotonic solution
crenation hemolysis
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Example Consider the following solutions
1M sugar 2M NaCl 1.5M Na2SO4 1M Ca(NO3)2
solution
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H. Colloidal dispersions A colloidal dispersion is a mixture in which a material is dispersed rather than dissolved.
. . . .. . . .
. . . .. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
. . . .
dispersed phase
Dispersing medium
10-7 – 10-5cm
Cannot be filtered
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Some proteins have size colloidal dispersion
solution colloidal dispersion
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I. Dialysis
Dialyzing membrane - has pores large enough to allow some ions and small molecules to pass along with water and gases.
Kidney cells, blood capillaries, intestinal walls, etc. function as dialyzing membranes.
Dialysis - the movement of ions and small molecules (urea), including water (solvent), across a dialyzing membrane.
Large molecules such as proteins cannot pass through a dialyzing membrane.
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Copyright © Houghton Mifflin Company. All rights reserved. 8–18
Figure 8.18 In dialysis, there is a net movement of ions from a region of higher concentration to a region of lower concentration. (a) Before dialysis. (b) After
dialysis.
Figure 8.18 In dialysis, there is a net movement of ions from a regionof higher concentration to a region of lower concentration.(a) Before dialysis. (b) After dialysis
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Copyright © Houghton Mifflin Company. All rights reserved. 8–19
Figure 8.19 Impurities (ions) can be removed from a solution by using a dialysis procedure.
Impurities (ions) can be removed from a solution byusing a dialysis procedure.
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Artificial kidney: a Hemodialysis Machine
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