Chapter 18: Solutions

Chapter 18: Solutions

Properties of Solutions

Chapter 18: Solutions-- Properties of Solutions --

Solution Formation• Formation of homogeneous mixtures• Factors that affect solution formation (dissolving)

– Nature of the solute and solvent– Amount of solute vs. solvent

• Factors that affect the rate of solution formation (dissolving)– Stirring (agitation)– Temperature– Surface area– Particle size


Solubility• How solution formation works

– Only so much solute will go into solution because, once room for a solute is not present, the particles going into solution are exchanged with particles coming out of solution.

– Partly responsible for precipitate formation


Solubility• Unsaturated solution

– A solution that contains less solute than a saturated solution– Most solutions are unsaturated

• Solubility of a substance– The amount of a substance that dissolves in a given quantity of solvent at a

given temperature to produce a saturated solution– Varies depending on temperature, kinds of solute and solvent, and other

factors• Miscibility

– Ability for two liquids to dissolve in each other– Example: ethanol and water

• Partial miscibility– Ability for two liquids to somewhat dissolve in each other– Example: water and diethyl ether


Solubility• Immiscibility

– Inability for two liquids to dissolve in each other– Example: petroleum and water

Factors Affecting Solubility• Temperature


Factors Affecting Solubility• Temperature (continued)

– As temperature increases, generally the solubility of a solid will increase.


Factors Affecting Solubility• Temperature (continued)

– As temperature increases, generally the solubility of a gas will decrease.


Factors Affecting Solubility• Pressure

– As the gas pressure above a solution increases, the gas solubility of the solvent increases.

– Gas is forced into solution more (I.e., greater solubility) if a greater gas pressure is exerted over the solution in order to keep the gas in the solution.

– Henry’s LawS1: solubility of the first solution

P1: gas pressure above the first solution

S2: solubility of the second solution

P2: gas pressure above the second solution


Factors Affecting Solubility• Supersaturated solution

– A solution that contains more than it theoretically should be able to hold at a given temperature

– Results from mixing at higher temperature or pressure

(a) (b) (c)(a): Supersaturated solution before a seed crystal is added(b): Solution after a seed crystal has been added(c): Excess solute in solution crystallizes rapidly


Concentrations of Solutions

Chapter 18: Solutions-- Concentrations of Solutions --

Molarity• Concentration of a solution

– A measure of the amount of solute that is dissolved in a given quantity of solvent

– Descriptions of concentration• Qualitative measures and expressions• Dilute solutions have only low concentrations of solute• Concentrated solutions have high concentrations of solute

– Molarity• Expressed as “M”• Number of moles of a solute dissolved per liter of solution

•


MolarityExample:Calculate the molarity of a solution made of 400.0 g CuSO4 in 4.00 L of solution.

Solution:


Molarity• Dilution of a solution

– The total number of moles before and after solution will remain the same since no solute is being added.

– Formula• M1: First solution’s molarity

• M2: Second solution’s molarity

• V1: First solution’s volume

• V2: Second solution’s volume•


MolarityExample:You have the following stock solutions available: 2.00M NaCl, …Calculate the volume you must dilute to make 500.0 mL of 0.500M NaCl.

Solution:


Percent Solutions• Percent by volume

– Expressed as % (v/v)

–

• Percent (mass/volume)– Expressed as % (m/v)–


Percent Solutions• Parts per million

– Expressed as ppm

–

– Used primarily for gas and living habitats– EPA usage– Other applications


Percent SolutionsExample:The Dead Sea contains 58 moles of lithium ion in 1.0 x 103 kg of seawater. Calculate the concentration, in ppm, of lithium ion in the Dead Sea.

Solution:


Colligative Properties of Solutions

Chapter 18: Solutions-- Colligative Properties --

Colligative Properties• A property of a solution that depends only on the number of solute

particles• Three colligative properties– Boiling point elevation– Vapor pressure lowering– Freezing point depression

• The more solute particles in solution, the more the property occurs– More particles, the more the boiling point is elevated– More particles, the more the vapor pressure is lowered– More particles, the more the freezing point is depressed


Colligative Properties• Example– If you have equal numbers of moles of CaCl2, AlCl3, NH4NO3, and

C6H12O6, which, when dissolved in solution, would have 1) the lowest freezing point, 2) the lowest vapor pressure, and 3) the lowest boiling point?

– CaCl2 Ca2+ + 2Cl– (3 particles per mole)

– AlCl3 Al3+ + 3Cl– (4 particles per mole)

– NH4NO3 NH4+ + NO3

– (2 particles per mole)

– C6H12O6 (1 particle per mole; molecular, so doesn’t dissociate)


Colligative Properties• Example– If you have equal numbers of moles of CaCl2, AlCl3, NH4NO3, and

C6H12O6, which, when dissolved in solution, would have 1) the lowest freezing point, 2) the lowest vapor pressure, and 3) the lowest boiling point?

– Lowest (most depressed) freezing point: AlCl3 • Most particles per mole (4)

– Lowest (most lowered) vapor pressure: AlCl3 • Most particles per mole (4)

– Lowest boiling point (opposite most elevated boiling point): C6H12O6 • Least particles per mole (1)

Chapter 18: Solutions

Documents

solutions chapter

expressionsdilute solutions

solution increases

gas solubility

greater gas pressure

solventamount of solute

kinds of solute

excess solute