Notes

Outline

Solution Chemistry

T-124  Hydration of Ions

Types of Solutions Solids in liquids Salt dissolved in water Liquid in a liquid Alcohol dissolved in water Gas in a liquid Carbonated water Gas in a Gas Air Gas in a solid (Hydrogen in Platinum) Liquid in a solid (Amalgam) Solid in a solid (Alloy)

Heats of Solution Heat of Solution-Energy exchange that takes place when a solution is formed Endothermic Heat of solution- Energy is absorbed as a solution is formed Exothermic Heat of Solution- Energy released when a solution is formed

T-126  Solubility Curves of Solids Dissolved in Water

Solutions and Hydrates Hydrate-Compound that has water molecules locked into the crystal structure (water of hydration) Test for Identifying a Hydrate Releases the water of hydration upon heating Anhydrous residues revert back to the original hydrate in the presence of water Anhydrous residue will dissolve in excess water and produce a solution with the same color as the original hydrate solid

Types of Concentration Concentration-The amount of solute in a given amount of solvent Types of Concentration Percent Mass/mass (m / m) Mass / volume (m / v) Volume / volume (v / v) Mole Fraction (X) Molarity (M) Molality (m)

Percent and ppm Mass Percent (m / m) % m/m = (mass of solute / mass solution) x 100 Mass / Volume Percent % m/v = (mass of solute / vol of solution) x 100 Volume / Volume Percent % v/v = (vol of solute / vol of solution) x 100 Parts Per Million (ppm) ppm = (mass of solute / mass of solution) x 10 6 Problem

Mole Fraction Mole Fraction (X) X 1 = mols of component 1 / total mols of all components X 1 + X 2 + X 3 + ….X n = 1

Molarity (M) Molarity (M) M = mols of solute / vol of solution in liters M = millimols of solute / vol of solution in ml Problems

Molality (m) Molality(m) m = mols of solute / kg of solvent

Concentration Conversion Given the mass Percent and density of solution determine: Mole fraction Molarity Molality

T-128  Calculations of Molarity and Molality

Solubility Solubility- amount of solute required to reach saturation with a given amount of solvent Unsaturated solution-solution below the solubility limit of a solution Saturated solution- solution at the solubility limit of a solution (solute and solvent in equilibrium with solution) Supersaturated solution- solution above the solubility limit of the solution (meta-stable state)

Factors Affecting Solubility Solute-solvent interaction Pressure Temperature

Solute-Solvent Interaction Hydrophilic groups of atoms attract water Hydrophobic groups of atoms repel water Alcohol solubility Relative solubility 1-4 carbon alcohols infinitely solubility in water 5-6 carbon alcohols are moderately soluble in water 7 carbon alcohols and  up are insoluble in water In general, the greater the molecular forces between solute and solvent molecules the greater the solubility For molecular substances, Hydrogen Bonding interactions are most influential

Gaseous aqueous solutions and Pressure Increasing the pressure of a gas over its solution increases the concentration of solution Diver’s Bends-collection of Nitrogen gas at joints due to release of gas as diver ascends too fast

Pressure Effect on Solubility of Gases

T-127 Solubility Curves of Gases in Water

Henry’s Law Henry’s Law-The concentration of a gas in a solvent is directly proportional to the pressure of that gas above the solution Cg = kPg   where k = Henry’s Constant for solvent     Cg is concentration of gas and Pg is the Pressure of gas above the solution Problem

Effect of Temperature on Solubility of a Gas Follows Equilibrium Laws since solubility is under saturated conditions where a dynamic equilibrium exists For endothermic Heats of solution: Increasing Temperature increases solubility For exothermic Heats of solution: Increasing the Temperature decreases the solubility

Colligative Properties Colligative Property-property that depends upon the number of particles in solution. Kinds of colligative properties: Vapor Pressure Lowering Boiling Point Elevation Freezing Point Depression Osmotic Pressure Elevation

Electrolytes Electrolyte-substance whose solution conducts an electrical current Requires the releasing of ions Greater the ion production in the solution the greater the conduction of current through the solution. HCl  +  H2O --à  H3O +   +   Cl – complete ionization= strong electrolyte HC2H3O2   +   H2O = H3O +    +   C2H3O2 -  Partial Ionization = weak electrolyte NaCl   +   H2O -à Na +(aq)  +  Cl –(aq)  Complete Dissociation = strong electrolyte

Non-Electrolytes Non-Electrolyte- substance whose solution does not conduct an electrical current. No ions produced during solution formation All particles in solution are molecular (no ions)

The “i-factor” i = number of mols of particles after solution formation / number of mols of particles before solution formation takes place C6H12O6(s)   +   H2O --à C6H12O6(aq) i = 1 / 1 = 1 Ca3(PO4)2   +   H2O ---à3Ca +2 (aq)  +  2PO4 –3 (aq) i = 5 / 1 = 5 For the same concentration of C6H12O6 and Ca3(PO4)2 the effect upon the colligative property will be 5 times greater in the Ca3(PO4)2 solution

Ion Pairing and Ideal Solutions In more concentrated solutions two or more ions act as a single particle thus the number of particles in solution is less than I factor would predict The more concentrated solutions would have colligative properties deviate from Ideal Solution Behavior In Ideal Solution assume that interionic particle attraction would approach zero. This would be more true if the concentration were decreased

T-131 Ion Pairing

Vapor Pressure Lowering Vapor Pressure of a solvent decreases as the concentration of solute increases(macroscopic View) Molecular View Explaination As more solute particles are added (increased concentration), they have a better chance of replacing surface solvent particles thus decreasing the chance for solvent particles to escape into vapor state.  An assumption is that the solute particles are relatively non-volatile and would not vaporize.

Raoult’s Law The vapor pressure of the solvent in a solution will decrease with decreasing solvent concentration (or increasing solute concentration) P1 = iX1P10  where P1 is Vapor press of solvent in solution ; X1 is mole fraction of solvent and P10 is the vapor press of pure solvent; i is the I factor of the solution Problem

Boiling Point Elevation Boiling Points are always elevated with increase in solute concentration Molecular view As the solute concentration is increased vapor pressure is decreased (Raoult’s Law).  The temperature of boiling would have to be greater to compensate for this lower vapor pressure

T-129 Vap Press vs Temperature of Pure Solvent and Solution

Boiling Point Elevation Equation Tb – Tb0 = i kb m where Tb is BP of solvent in solution; Tb0 is B.P. of pure solvent; kb is boiling point elevation constant for solvent; m is the molal concentration; i is the i-factor for solution. Problem

T-129  Vap Press vs Temp for Pure Solvent and Solution

Freezing Point Depression Freezing Point decreases with increasing solute concentration. Molecular View As solute particles increase they are more likely to take the place of the solvent particles in the crystal lattice thus weakening the crystal structure and making the crystal structure more likely to collapse at a lower temperature (lower kinetic energy)

Freezing Point Depression Equation Tf 0 – Tf = i kf m      where Tf 0 is the Freezing Point of pure solvent; Tf is the Freezing Point of the solvent in the solution; kf is the Freezing Point Depression Constant of the solvent; m is the molal concentration; i is the i-factor of the solution. Problem

T-129

Osmotic Pressure Elevation Osmotic Pressure-Pressure difference between a solution and a pure solvent Osmotic Pressure increases with increasing solute concentration (macro view) Molecular View As the number of solute particles increase there are fewer solvent molecules that can pass from one side of a semi-permeable membrane to the less concentrated side but more water molecules will be able to pass to the more concentrated side People on an elevator analogy

T-130 Osmosis

T-12.22  An experiment in Osmosis

Osmotic Pressure Equation Pi = i M R T    where Pi is the Osmotic pressure; M is the Molarity concentration; R is the universal Gas Law Constant; T is the Kelvin Temperature; i is the i-factor for the solution Problem

Isotonic, Hypotonic and Hypertonic Solutions Isotonic solution-solutions of the same concentrationas solution on the other side of membrane Hypotonic solutions-solutions of smaller concentration compared to concentration of solution on the other side of membrane Hypertonic solution-solution of a higher concentration than solution on the other side of membrane

Cell size and Osmosis When cells are : Isotonic  the cells have just as much water entering as is leaving hence no change Hypotonic the cells have more water leaving the cell than can enter hence cells shrink in size because of water loss(crenation) Hypertonic the cells have more water entering the cell than exits and the cells swell(hemolysis) In general,osmosis always occurs from the less concentrated side to the more concentrated side(increased entropy)

Determining Molar Mass Using Colligative Property Data Using Boiling Point Elevation or Freezing Point Depression Data MM = I k (mass of solute) / kg of solvent ( Delta T) Problem Using Osmotic Pressure Data MM = i (mass of solute)R T / Osmotic Pressure(Volume of solution in liters) Problem