Properties of Solutions

Terminology Solution = A homogeneous mixture. Solute = a substance dissolved in a solvent to form a solution; usually the smaller portion. Solvent = The dissolving medium of a solution; usually the greater portion. Solubility = Amount of substance dissolved. Dilute , Concentrated , Saturated .

The Solution Process

Figure 13.2: The Solution Process Hydration or Solvation

The Solution Process Solution Formation, Spontaneity, and Disorder If the process leads to a greater state of disorder, then the process is spontaneous. Example: a mixture of CCl4 and C6H14 is less ordered than the two separate liquids. Therefore, they spontaneously mix even though Hsoln is very close to zero. There are solutions that form by physical processes and those by chemical processes.

Factors Affecting Solubility Solute-Solvent Interaction Miscible liquids: mix in any proportions. Immiscible liquids: do not mix. [ Oil and Vinegar ] Generalization: “like dissolves (in) like”. Polar liquids tend to dissolve in polar solvents.

Ways of Expressing Concentration Mass Percentage All methods involve quantifying amount of solute per amount of solvent (or solution). Generally amounts or measures are masses, moles or liters.

Ways of Expressing Concentration Mole Fraction, Molarity, and Molality

Solution Compositions s = solute ; A = solvent; V = Tot. Vol. of solution. Weight %: Mole Fraction: Molarity: Molality:

Example of Solution Compositions A solution is prepared by mixing 78.9 g of ethanol (C2H5OH) with 100.0 g of water to give 190.5 mL of solution. Calculate the solution compositions. The electrolyte in automobile lead storage batteries is a 3.75 M H2SO4 solution that has a density of 1.230 g/mL. Calculate mass %, molality, and mole fraction in terms of H2SO4 . [Hint: Assume exactly one liter of solution.] [Answers: 29.9% , 4.35 molal, 0.0727 ]

s = ethanol (solute); A = water (solvent);

Concentrations of Solutions In the Dilution process of a more concentrated solution: The number of moles are the same in diluted and concentrated solutions. So: MdiluteVdilute = moles = MconcentratedVconcentrated

General Properties of Aqueous Solutions Electrolytic Properties Three types: Strong electrolytes, Weak electrolytes, and Nonelectrolytes.

General Properties of Aqueous Solutions Strong and Weak Electrolytes Strong electrolytes: completely dissociated in solution. e.g. Weak electrolytes: produce small concentration of ions when dissolved.

Precipitation Reactions

Precipitation Reactions Exchange (Metathesis) Reactions Metathesis reactions involve swapping ions in solution: AX + BY  AY + BX.

Precipitation Reactions Ionic Equations Ionic equation: used to highlight reaction between ions. Molecular equation: all species listed as molecules: AgNO3(aq) + NaI(aq)  AgI(s) + NaNO3(aq) Complete ionic equation(CIE): lists all ions: Ag+(aq) + NO3-(aq) + Na+(aq) + I-(aq)  AgI(s) + Na+(aq) + NO3-(aq) Net ionic equation: cancel spectator ions from CIE Ag+(aq) + I-(aq)  AgI(s)

Figure 13.14: Factors Affecting Solubility Intermolecular Forces Pressure Temperature

Figure 13.14: Factors Affecting Solubility Pressure Effects

Factors Affecting Solubility Pressure Effects If Sg is the solubility of a gas, k is a constant, and Pg is the partial pressure of a gas, then Henry’s Law gives: Carbonated beverages are bottled with a partial pressure of CO2 >1 atm, ( pressure inside can ~4 atm above liq). As bottle is opened, partial pressure of CO2 decreases and solubility of CO2 decreases. Therefore, bubbles of CO2 escape from solution. CyberChem Diving Gases

Factors Affecting Solubility Temperature Effects: Solids in Liquids Generally, as temperature increases, solubility of solids generally increases, BUT Sometimes, solubility decreases as temperature increases (e.g. Ce2(SO4)3).

Figure 13.18

Factors Affecting Solubility Temperature Effects: Gases in Liquids Gases get less soluble as temperature increases. Thermal pollution: if lakes get too warm, CO2 and O2 become less soluble and are not available for plants or animals.

Figure 13.18

Colligative Properties Colligative properties depend on quantity of solute molecules. (e.g. freezing point depression and boiling point elevation.) Lowering Vapor Pressure Non-volatile solutes reduce the ability of the surface solvent molecules to escape the liquid. Therefore, vapor pressure is lowered. The amount of vapor pressure lowering depends on the amount of solute.

Figure 11.22: Vapor Pressure Vapor Pressure on the Molecular Level

Figure 11.24

Figure 11.26: Phase Diagrams

Figure 11.27: Phase Diagrams The Phase Diagrams of H2O and CO2

Figure 13.20: Colligative Properties Lowering Vapor Pressure

Colligative Properties Lowering Vapor Pressure Raoult’s Law: Where: PA = vapor pressure with solute, PA = vapor pressure without solute (pure solvent), and A = mole fraction of A.

Vapor Pressure Examples Calculate the expected vapor pressure at 25oC for a solution prepared by dissolving 158.0 g of common table sugar (sucrose – MW=342.3) in 643.5 mL of water. At 25oC, the density of water is 0.9971 g/mL and the vapor pressure is 23.76 torr. A solution was prepared by adding 20.0 g of urea to 125 g of water at 25oC, a temperature at which pure water has a vapor pressure of 23.76 torr. The observed vapor pressure of the solution was found to be 22.67 torr. Calculate the molecular weight of urea. [Answer: 60. g/mol ]

Calculate the expected vapor pressure at 25oC for a solution prepared by dissolving 158.0 g of common table sugar (sucrose – MW=342.3) in 643.5 mL of water. At 25oC, the density of water is 0.9971 g/mL and the vapor pressure is 23.76 torr.

Figure 13.22

Colligative Properties Boiling-Point Elevation Molal boiling-point-elevation constant, Kb, expresses how much Tb changes with molality, mS : Decrease in freezing point (Tf) is directly proportional to molality (Kf is the molal freezing-point-depression constant):

Colligative Properties

Applications of Colligative Properties A solution was made by dissolving 18.00 g of glucose in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34oC. Calculate the molecular weight of glucose. How many kg of ethylene glycol (C2H6O2, MW=62.1), antifreeze, must be added to 10.0 L of water to produce a solution for use in a car’s radiator that freezes at –23.3oC? Assume that the density of water is 1.00 g/mL. [Answer: 7.78 kg (with d = 1.18 g/mL => 6.59 L)]

A solution was made by dissolving 18. 00 g of glucose in 150 A solution was made by dissolving 18.00 g of glucose in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34oC. Calculate the molecular weight of glucose.

A solution was made by dissolving 18. 00 g of glucose in 150 A solution was made by dissolving 18.00 g of glucose in 150.0 g of water. The resulting solution was found to have a boiling point of 100.34oC. Calculate the molecular weight of glucose.

How many kg of ethylene glycol (C2H6O2, MW=62 How many kg of ethylene glycol (C2H6O2, MW=62.1), antifreeze, must be added to 10.0 L of water to produce a solution for use in a car’s radiator that freezes at –23.3oC? Assume that the density of water is 1.00 g/mL.

Colligative Properties: Homework due for Friday Dec. ?, 201?. What is the molecular weight (g/mol) of a non-volatile solute if 7.32 kg of this solute dissolved in 10.0 L of water produced a solution with a freezing point of -23.3C? Assume density of water as 1.00 g/mL.

Colligative Properties Osmosis movement of a solvent from low solute concentration to high solute concentration across a semipermeable membrane. Figure 13.23

Colligative Properties Osmosis Osmotic pressure, , is the pressure required to stop osmosis:

Application of Osmotic Pressure To determine the molecular weight of a certain protein, 1.00 mg of it was dissolved in enough water to make 1.00 mL of solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0oC. Calculate the molecular weight of the protein. [Answer: 1.66x104 g/mol]

To determine the molecular weight of a certain protein, 1 To determine the molecular weight of a certain protein, 1.00 mg of it was dissolved in enough water to make 1.00 mL of solution. The osmotic pressure of this solution was found to be 1.12 torr at 25.0oC. Calculate the molecular weight of the protein.

Colligative Properties Osmosis Isotonic solutions: two solutions with the same  separated by a semipermeable membrane. Osmosis is spontaneous. Red blood cells are surrounded by semipermeable membranes.

Figure 13.25: Colligative Properties Osmosis Crenation: hypertonic solution Hemolysis: hypotonic solution IV(intravenous) fluids must be Isotonic. CyberChem: Desalination

Colloids Colloids are suspensions in which the suspended particles are larger than molecules but too small to drop out of the suspension due to gravity. Particle size: 10 to 2000 Å. Tyndall effect: ability of a Colloid to scatter light. The beam of light can be seen through the colloid.

Colloids

Figure 13.31: Colloids

Properties of Solutions