READING FOR TUESDAY: Chapter 12 sections 3 – 5 READING FOR TUESDAY: Chapter 12 sections 3 – 5 HOMEWORK – DUE THURSDAY 11/19/15 HOMEWORK – DUE THURSDAY 11/19/15 HW-BW 10.2 CH 10 #’s 72, 73, 75, 78, 79, 88, 93, 93 HW-BW 10.2 CH 10 #’s 72, 73, 75, 78, 79, 88, 93, 93 HW-BW 11 CH 11 #’s 1-12 (all), (even), 25 HW-BW 11 CH 11 #’s 1-12 (all), (even), 25 HOMEWORK – DUE Tuesday 11/24/15 HOMEWORK – DUE Tuesday 11/24/15 HW-WS 18 (Worksheet) (from course website) HW-WS 18 (Worksheet) (from course website) Lab Lab Wednesday/Thursday – EXP 14 continued Wednesday/Thursday – EXP 14 continued Exam 4 Next Tuesday Exam 4 Next Tuesday

Solutions Solution – A system in which one or more substances are mixed or dissolved in another substance. Solution – A system in which one or more substances are mixed or dissolved in another substance. Solute – The substance that is being dissolved, or the least abundant component, of a solution. Solute – The substance that is being dissolved, or the least abundant component, of a solution. Solvent – The dissolving agent or the most abundant component in a solution. Solvent – The dissolving agent or the most abundant component in a solution. A solute goes into a solvent to make a solution (solute + solvent = solution) A solute goes into a solvent to make a solution (solute + solvent = solution)

Time to Concentrate! Solutions have variable composition Solutions have variable composition The concentration of a solution tells us how much solute is dissolved in a given quantity of solution. The concentration of a solution tells us how much solute is dissolved in a given quantity of solution. Many measurements for the concentration of a solution: Many measurements for the concentration of a solution: volume/volume percent volume/volume percent mass/mass percent mass/mass percent ppm (parts-per-million) ppm (parts-per-million) molarity molarity osmolarity osmolarity mole fraction mole fraction molality molality

molarityosmolarity 1.5 M C 6 H 12 O 6(aq) 1.5 osmol C 6 H 12 O 6(aq) stays as 1 piece 1.5 M NaCl (aq) 3.0 osmol NaCl (aq) breaks into 2 pieces 1.5 M BaCl 2(aq) 4.5 osmol BaCl 2(aq) breaks into 3 pieces 1.5 M Al 2 (SO 4 ) 3(aq) 7.5 osmol Al 2 (SO 4 ) 3(aq) breaks into 5 pieces Time to Concentrate on Osmolarity!

Time to Concentrate!

Moles of solute per 1 kilogram of solvent Moles of solute per 1 kilogram of solvent defined in terms of amount of solvent, not solution defined in terms of amount of solvent, not solution Does not vary with temperature Does not vary with temperature Used mostly in freezing-point depression and boiling-point elevation calculations Used mostly in freezing-point depression and boiling-point elevation calculations When molality is given, it is ALWAYS per 1 kg When molality is given, it is ALWAYS per 1 kg Time to Concentrate on Molality, m!

What is the molality of a solution prepared by mixing 17.2 g of C 2 H 6 O 2 with 475 g of H 2 O to make 480 mL of solution?

Colligative Properties Colligative properties are properties whose value depends only on the number of solute particles, and not on what they are Colligative properties are properties whose value depends only on the number of solute particles, and not on what they are Value of the property depends on concentration of the solution Value of the property depends on concentration of the solution Osmotic pressure Osmotic pressure Directly related to concentration Directly related to concentration Vapor pressure Vapor pressure Inversely related to concentration Inversely related to concentration Boiling point Boiling point Rises with added solute, change is directly related to concentration Rises with added solute, change is directly related to concentration Freezing point Freezing point Drops with added solute, change is directly related to concentration Drops with added solute, change is directly related to concentration

Colligative Properties – Freezing Point The freezing point of a solution is always lower than the freezing point of the pure solvent The freezing point of a solution is always lower than the freezing point of the pure solvent Hence freezing point DEPRESSION Hence freezing point DEPRESSION The difference between the freezing point of the solution and freezing point of the pure solvent is directly proportional to the molality of solute particles The difference between the freezing point of the solution and freezing point of the pure solvent is directly proportional to the molality of solute particles The proportionality constant is called the Freezing Point Depression Constant, K f The proportionality constant is called the Freezing Point Depression Constant, K f K f depends on the solvent K f depends on the solvent the units of K f are °C/m the units of K f are °C/m  T f = change from normal boiling point K f = solvent dependent constant m = molality of solution i = van’t Hoff factor

Colligative Properties – van’t Hoff Factor Ionic compounds produce multiple solute particles for each formula unit Ionic compounds produce multiple solute particles for each formula unit The theoretical van’t Hoff factor, is the ratio of moles of solute particles to moles of formula units dissolved The theoretical van’t Hoff factor, is the ratio of moles of solute particles to moles of formula units dissolved NaCl makes 2 particles NaCl makes 2 particles CaCl 2 makes 3 particles CaCl 2 makes 3 particles AlCl 3 makes 4 particles AlCl 3 makes 4 particles Al 2 (SO 4 ) 3 makes 5 particles Al 2 (SO 4 ) 3 makes 5 particles C 6 H 12 O 6 makes 1 particle C 6 H 12 O 6 makes 1 particle The measured van’t Hoff factors are generally less than the theoretical due to ion pairing in solution The measured van’t Hoff factors are generally less than the theoretical due to ion pairing in solution so the measured van’t Hoff factor often causes the  T to be smaller than expected so the measured van’t Hoff factor often causes the  T to be smaller than expected

Colligative Properties – van’t Hoff Factor

Colligative Properties – Freezing Point What is the freezing point of a salt water solution made from grams of NaCl in kg of water? (K f,water = 1.86 °C/m) FP solution = FP water –  T f FP solution = 0.00 o C – 1.27 o C FP solution = – 1.27 o C

Intermolecular Forces Intramolecular or bonding forces are found within a molecule. The chemical behavior of each phase of matter is the same because the same constituent particle is present in each case. Intramolecular or bonding forces are found within a molecule. The chemical behavior of each phase of matter is the same because the same constituent particle is present in each case. H 2 O molecules are present whether the substance is in the solid, liquid, or gas phase. H 2 O molecules are present whether the substance is in the solid, liquid, or gas phase. Intermolecular or nonbonding forces are found between molecules. The physical behavior of each phase of matter is different because the strength of these forces differs from state to state. Intermolecular or nonbonding forces are found between molecules. The physical behavior of each phase of matter is different because the strength of these forces differs from state to state. Intermolecular forces are relatively weak compared to intramolecular forces because they involve smaller charges that are farther apart. Intermolecular forces are relatively weak compared to intramolecular forces because they involve smaller charges that are farther apart.

Intermolecular forces are the attractions BETWEEN separate particles! Intermolecular forces are the attractions BETWEEN separate particles! Can be used to predict general trends in some physical properties. Can be used to predict general trends in some physical properties. The stronger the attractive forces are, the higher will be the boiling point of the liquid and the melting point of the solid The stronger the attractive forces are, the higher will be the boiling point of the liquid and the melting point of the solid Solids melt when heated because the particles gain enough kinetic energy to partially overcome (loosen) the attractive forces Solids melt when heated because the particles gain enough kinetic energy to partially overcome (loosen) the attractive forces Liquids boil when heated because the particles gain enough kinetic energy to completely overcome (break) the attractive forces Liquids boil when heated because the particles gain enough kinetic energy to completely overcome (break) the attractive forces Intermolecular Forces