aqueous solutions solution: homogeneous mixture; solid liquid, or gas soluble: capable of being...
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Aqueous Solutions
Solution: Homogeneous mixture; solid liquid, or gas
Soluble: Capable of being dissolvedSolute: Substance that is dissolved,
present in lesser amountsSolvent: Dissolving medium; present
in greater amounts
Types of MixturesSolutions: particles < 1nm; cannot be
seen; no scattering of light (salt water)Suspensions: particles > 100 nm; settle to
the bottom (sand & water)Colloids: particles 1-100 nm; suspended
throughout the medium; exhibit Tyndall effect
Tyndall Effect: Scattering of light so that the beam of light can be seen like headlights in fog; seen in colloids
Hydration
Hydrates: ionic compounds with water molecules in their structure specific ratios of water to compoundheating can drive off the water and leave the
anhydrous salt
CuSO4 • 5H2O (copper (II) sulfate pentahydrate
HydratesEffloresce: If a hydrate has a vapor pressure
greater than water vapor, than it will lose its water of hydration
Hygroscopic: Hydrated salts that have a low vapor pressure remove water from moist air to form higher hydratesUsed as drying agents or desiccants Silica gel
Deliquescent: remove sufficient water from the air to dissolve completely and form solutions
Types of SolutesElectrolytes: Conduct an electric current when
dissolvedAll Ionic CompoundsPolar Molecules when dissolved in water (ionized)Weak Electrolyte: fraction of the solute exist as ionsStrong Electrolyte: almost all of the solute exist as
separate ions
Nonelectrolytes: Do not conduct an electric current when dissolvedCovalent compoundsPolar Molecules in a pure state
Dissociation
Sodium Chloride:
NaCl(s) Na+1(aq) + Cl-1
(aq)
Magnesium nitrate:
Mg(NO3)2(s) Mg+2(aq) + 2NO3
-1(aq)
Dissociation is the “breaking apart” of ions as an ionic compound dissolves in water.
Factors Affecting Rate of Dissolution
Surface Area: Greater surface area (smaller particle size) = faster dissolution
Agitation: stirring = faster dissolutionHeating: generally means faster
dissolution
Like Dissolves Like
The polarity of water molecules plays an important role in the formation of solutions of ionic compounds and other polar compounds in water.
The positive ends of the water molecules attract negative ions (dipoles) and the negative ends of water molecules attract positive ions (dipoles), pulling them from the surface of the crystal.
Miscible/Immiscible
Nonpolar molecules do not attract ions of crystalline solids strongly enough to overcome forces holding them together and therefore cannot dissolve polar or ionic compounds.
Miscible : Two liquids mix; soluble in one another (Ex: Ethanol & Water)
Immiscible: Do not mix; insoluble in one another (Ex: Oil & Water)
Relative ConcentrationConcentration: a measure of the amount of
solute that is dissolved in a given quantity of solvent
Unsaturated: Less than the theoretical amount of solute is dissolved; there is room to dissolve more
Saturated: The maximum amount of solute that can be dissolved at a certain temperature has been reached
Supersaturated: More than the theoretical amount of solute is dissolved in solvent at a given temperature
Solubility/RecrystallizationSolubility:
A measure of how much solute can dissolve in a given amount of solvent at a specific temperature
Dilute Solution: The amount of solute dissolved is small in relation to the amount of solvent present.
Concentrated Solution: The amount of solute dissolved is large in relation to the amount of solute present.
At the same time substances are breaking apart, there are also particles attracted to each other and remaining together – RECRYSTALLIZATION
Solution Equilibrium: Rate of dissolution = Rate of recrystallization
Saturation Curve
°C
0
0
20
40
60
80
140
100
120
160
180
g / 100 mL
10 20 40 60 80 10030 50 70 90
Supersaturated Saturated
Unsaturated
Changing the temperature of a solvent can have an effect on solubility!!
°C
0
0
20
40
60
80
140
100
120
160
180
g / 100 mL
10 20 40 60 80 10030 50 70 90
A
B
Which solute has the greatest solubility at 20°C?
Which solute has the greatest solubility at 50°C?
Gas SolubilityHenry’s Law: S1
/P1 = S2 / P2
The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid.
Open a can of pop!! Carbon dioxide is forced into solution of flavored water at 5-10 atm.
Effervescence: The FIZZING that happens when you open the pop; the release of gas from a solution
Concentrations of Solutions
Molarity = M = mol solute
L solutionMolality = m = mol solute
kg solventPercent by mass [% m/v] = mass solute x 100
mL solutionPercent by volume [% v/v] = vol solute x 100
vol solution
DilutionsYou have the following stock solutions
available: 2.0 M NaCl; 4.0 M KNO3; 0.5M MgSO4
Calculate the stock volumes you must dilute to make the following solutions using
M1V1 = M2V2
500 mL of a 0.50 M sodium chloride solution
2.0 L of a .20 M magnesium sulfate solution
Examples/Molarity
What is the molarity of a solution that contains 212.5 g of sodium nitrate (NaNO3) in 3.0 liters of solution?
What mass of sucrose, C12H22O11 is needed to make 300 mL of a 0.50 M solution?
Examples/MolalityCalculate the molality of a solution made
by dissolving 45.0 g of dextrose, C6H12O6 in 500.0 g of water.
What is the mass of water required to prepare a 1.00 molal solution containing 10.0 g of NaOH?
Calculate the molality of a solution prepared by dissolving 6.3 moles of KCN in 633 g of water
Percent Problems% m/v: Calculate the number of grams of
solute required to make the following solutions:2.5 L of saline solution– 90% NaCl50 mL of 4% magnesium chloride
%v/v: 10 mL acetic acid is diluted with water to a total solution volume of 200 mL. What is the % v/v of acetic acid?
25mL of ethanol and 75 mL of water are mixed. What is the % v/v of the solution?
Colligative Properties
Depend only on the number of particles dissolved in a given mass of solventVapor Pressure LoweringBoiling Point ElevationFreezing Point Depression
Vapor Pressure LoweringA nonvolatile solute has a lower vapor pressure
than a pure solventAs solutes are added the equilibrium is
disrupted and solvent particles form shells around the solute particles. This reduces the number of free solvent particles able to escape the liquid. Equilibrium is eventually re-established at a lower vapor pressure
Decrease in VP is proportional to the number of particles the solute makes in solutionSolute that disassociate in large #s have a greater
effect of VP
Boiling Point ElevationThe difference in temperature between the
boiling point of a solution & that of a pure solvent
Boiling points of solutions are higher than that of pure solvents The presence of solutes increase BP
Additional KE is required for particles to overcome the attractive forces that keep them in liquid
Boiling Point elevation (ΔTb): directly proportional to the molal concentrationΔTb α m ΔTb = Kb x m
Freezing Point DepressionThe Difference in temperature between
the freezing point of a solution and that of the pure solvent
More KE must be withdrawn from a solution than from a pure solution to solidify
Freezing Point Depression (Δ Tf): directly proportional to the molal concentrationΔ Tf = Kf x m