Solutions Chapter 13 and 14 Honors Chemistry

Solution Definition: a homogeneous mixture of 2 or more substances in a single physical state Definition: a homogeneous mixture of 2 or more substances in a single physical state Parts: solute and solvent (usually water) Parts: solute and solvent (usually water)

Types of solutions Physical states: solid (alloys), liquid, gas Physical states: solid (alloys), liquid, gas Miscible vs. Immiscible Miscible vs. Immiscible Miscible - liquids that dissolve freely in one another in any proportion Miscible - liquids that dissolve freely in one another in any proportion Immiscible - liquid solutes and solvents that are not soluble Immiscible - liquid solutes and solvents that are not soluble Dilute vs. Concentrated Dilute vs. Concentrated Electrolyte vs. Nonelectrolyte Electrolyte vs. Nonelectrolyte Saturated, Unsaturated and Supersaturated Saturated, Unsaturated and Supersaturated

Supersaturated Solution demo

Electrolyte vs. Nonelectrolyte

Saturated – soln containing the max amt of solute Saturated – soln containing the max amt of solute Unsaturated – soln containing less solute than a sat soln under the existing conditions Unsaturated – soln containing less solute than a sat soln under the existing conditions Supersaturated – contains more dissolved solute than a saturated solution under the same conditions Supersaturated – contains more dissolved solute than a saturated solution under the same conditions Solubility Curves

supersaturated solution (stirred)

Solubility (physical change) Definition: mass of solute needed to make a saturated solution at a given temperature Definition: mass of solute needed to make a saturated solution at a given temperature solution equilibrium in a closed system solution equilibrium in a closed system dissolution ↔ crystallization dissolution ↔ crystallization Unit = g solute/100 g H 2 O Unit = g solute/100 g H 2 O

Saturated sol’n Supersaturated solution Unsaturated solution At 20 o C, a saturated solution contains how many grams of NaNO 3 in 100 g of water? What is the solubility at 70 o C? 135 g/100 g water What kind of solution is formed when 90 g NaNO 3 is dissolved in 100 g water at 30 o C? unsaturated What kind of solution is formed when 120 g NaNO 3 is dissolved in 100 g water at 40 o C? supersaturated 90 g

Solubility of solids in liquids For most solids, increasing temperature, increases solubility. For most solids, increasing temperature, increases solubility. In general, “like dissolves like”. Depends on In general, “like dissolves like”. Depends on Type of bonding Type of bonding Polarity of molecule Polarity of molecule Intermolecular forces between solute and solvent Intermolecular forces between solute and solvent

Solubility of Gases Gases are less soluble at high temperatures than at low temperatures Gases are less soluble at high temperatures than at low temperatures Increasing temperature, decreases solubility. Increasing temperature, decreases solubility. Increasing pressure, increases solubility. Increasing pressure, increases solubility.

The quantity of gas that dissolves in a certain volume of liquid is directly proportional to the pressure of the gas (above the solution). The quantity of gas that dissolves in a certain volume of liquid is directly proportional to the pressure of the gas (above the solution).

Effervescence – rapid escape of gas dissolved in liquid Effervescence – rapid escape of gas dissolved in liquid

Factors Affecting Solubility Increase surface area of solute (crushing) Increase surface area of solute (crushing) Stir/shake Stir/shake Increase temperature Increase temperature

Dissolution Process Ionic Compounds Ionic Compounds NaCl (s)  Na +1 (aq) + Cl -1 (aq) For dissolution to occur, must overcome solute attractions and solvent attractions. For dissolution to occur, must overcome solute attractions and solvent attractions. Dissociation Reaction : the separation of IONS when an ionic compound dissolves (ions already present) Dissociation Reaction : the separation of IONS when an ionic compound dissolves (ions already present) Try calcium chloride Try calcium chloride hexahydrated for Na +1 ; most cations have 4-9 H 2 O molecules 6 is most common Solvation : process of solvent molecules surrounding solute Hydration : solvation with water nonelectrolyte electrolyte Dissolving NaCl in water

Dissolution Process Molecular Compounds Molecular Compounds Nonpolar molecular solids do not dissolve in polar solvents Nonpolar molecular solids do not dissolve in polar solvents naphthalene naphthalene Polar molecule Polar molecule C 12 H 22 O 11 (s)  C 12 H 22 O 11 (aq) C 12 H 22 O 11 (s)  C 12 H 22 O 11 (aq) Molecular solvation Molecular solvation Nonelectrolyte Nonelectrolyte Polar molecule Polar molecule HCl(g)  H +1 (aq) + Cl -1 (aq) or HCl(g)  H +1 (aq) + Cl -1 (aq) or HCl(g) + H 2 O  H 3 O +1 (aq) + Cl -1 (aq) HCl(g) + H 2 O  H 3 O +1 (aq) + Cl -1 (aq) Ionization : ions formed from solute molecules by action of solvent (no ions initially present) Ionization : ions formed from solute molecules by action of solvent (no ions initially present) Nonelectrolyte (HCl)  electrolyte (ions) Nonelectrolyte (HCl)  electrolyte (ions)

Energy Changes Heat of solution =  H soln Heat of solution =  H soln Endothermic Endothermic Solute particles separating in solid Solute particles separating in solid Solvent particles moving apart to allow solute to enter liquid Solvent particles moving apart to allow solute to enter liquid Energy absorbed Energy absorbed Exothermic Exothermic Solute particles separating in solid Solute particles separating in solid Solvent particles attracted to solvating solute particles Solvent particles attracted to solvating solute particles Energy released Energy released  H soln = heat of solvation – crystal lattice energy

Solution Reactions Single replacement Single replacement Activity Series Activity Series Double replacement Double replacement Solubility chart (soluble vs. insoluble) Solubility chart (soluble vs. insoluble) Neutralization (water) Neutralization (water) Gases (CO 2 and H 2 S) Gases (CO 2 and H 2 S)

Concentration Percent concentration by mass (mass %) Percent concentration by mass (mass %) (solute/solution) x 100% = % Concentration (solute/solution) x 100% = % Concentration Molarity (M) Molarity (M) Moles of solute/Liters of solution = mol/L Moles of solute/Liters of solution = mol/L Molality (m) Molality (m) Moles of solute/mass of solvent = mol/kg Moles of solute/mass of solvent = mol/kg ppm and ppb ppm and ppb Used for very dilute solutions Used for very dilute solutions Dilution – a process in which more solvent is added to a solution Dilution – a process in which more solvent is added to a solution How is this solution different? How is this solution different? Volume, color, molarity Volume, color, molarity How is it the same? How is it the same? Same mass of solute, same moles of solute Same mass of solute, same moles of solute In Dilution ONLY: M 1 V 1 = M 2 V 2 In Dilution ONLY: M 1 V 1 = M 2 V 2

Colligative Properties Definition: physical properties of solutions that differ from properties of its solvent. Definition: physical properties of solutions that differ from properties of its solvent. Property depends upon the number of solute particles in solution. Property depends upon the number of solute particles in solution. Types: Types: 1. Vapor Pressure 2. Boiling Point ELEVATION 3. Freezing Point DEPRESSION

Vapor Pressure A measure of the tendency of molecules to escape from a liquid For nonvolatile liquids or solid solutes For nonvolatile liquids or solid solutes A nonvolatile solute will typically increase the boiling point and decrease the freezing point. A nonvolatile solute will typically increase the boiling point and decrease the freezing point. Adding a nonvolatile solute lowers the concentration of water molecules at the surface of the liquid. Adding a nonvolatile solute lowers the concentration of water molecules at the surface of the liquid. This lowers the tendency of the water molecules to leave the solution and enter the gas phase. This lowers the tendency of the water molecules to leave the solution and enter the gas phase. Therefore the vapor pressure of the solution is LESS than pure water. Therefore the vapor pressure of the solution is LESS than pure water.

H2OH2OH2OH2O H2OH2OSugar H 2 O Same Temperature Temperature (ºC) Vapor Pressure (kPa) H2OH2Osolution

Boiling Point Elevation  t b = boiling point elevation  t b = boiling point elevation  t b = iK b m  t b = iK b m i = molality conversion factor; for electrolytes adjust for # of ions actually present in solution (dissociation process) i = molality conversion factor; for electrolytes adjust for # of ions actually present in solution (dissociation process) K b = molal bp elevation constant K b = molal bp elevation constant K b = 0.512°C·kg H 2 O K b = 0.512°C·kg H 2 O moles of solute (ions or molecules) moles of solute (ions or molecules) m = molality = moles solute m = molality = moles solute kg of solvent kg of solvent bp of solution = bp of solvent +  t b bp of solution = bp of solvent +  t b

Boiling Point Elevation and Freezing Point Problems 1. At what temperature will a solution begin to boil if it is composed of 1.50 g potassium nitrate in 35.0 g of water? Solute: Solute: 2. At what temperature will a solution begin to freeze when 18.0 g ammonium phosphate is dissolved in g water? Solute: Solute:

Freezing Point Depression when a solution freezes, the solvent solidifies as a pure substance; deviates for more concentrated solutions  t f = freezing point depression  t f = freezing point depression  t f = iK f m  t f = iK f m i = molality conversion factor; for electrolytes adjust for # of ions actually present in solution (dissociation process) i = molality conversion factor; for electrolytes adjust for # of ions actually present in solution (dissociation process) K f = molal freezing point depression constant K f = molal freezing point depression constant K f = 1.858°C·kg H 2 O K f = 1.858°C·kg H 2 O moles of solute (ions or molecules) moles of solute (ions or molecules) m = molality = moles solute m = molality = moles solute kg of solvent kg of solvent fp of solution = fp of solvent -  t f fp of solution = fp of solvent -  t f

Osmotic Pressure The external pressure needed to stop osmosis The external pressure needed to stop osmosis Osmosis is the movement of solvent through a semi permeable membrane from lower concentration to higher concentration Osmosis is the movement of solvent through a semi permeable membrane from lower concentration to higher concentration

the pressure required to allow for no transport of solvent across the membrane is called the OSMOTIC pressure