Presentation on theme: "Welcome to Chem 121-01 è HAPPY NEW YEAR !!! è Pick up CAPA #1 - outside on shelf è Pick up syllabus - in front è Get your photo taken - get index card."— Presentation transcript:
Welcome to Chem 121-01 è HAPPY NEW YEAR !!! è Pick up CAPA #1 - outside on shelf è Pick up syllabus - in front è Get your photo taken - get index card
Outline:1/10/07 n n Go over course syllabus What to expect? n Plus ça change: n Plus la même chose: ACS standardized final (cumulative over two semesters) CAPA, keypads, text & lectures…
Outline:1/10/07 n n Any questions? Do DISCUS post assignment… Read Chapter 12…try CAPA early…
Outline:1/10/07 n n Any questions? n n Start chapter 12 - Solutions Solution properties Colligative properties
Some Aqueous Properties: n n Solution: n n Solvent: n n Solute: n n Aqueous Solution: n Homogenous mixture of 2 or more components n Majority component of solution n Minority component of solution n Solvent is H 2 O, denoted as species (aq)
More Definitions A solution holding the maximum solute is...saturated A solution holding the maximum solute is...saturated A solution that can hold more solute is...unsaturated A solution that can hold more solute is...unsaturated A solution that is holding too much solute is...supersaturated A solution that is holding too much solute is...supersaturated
Supersaturated Sodium Acetate A supersaturated solution of NaCH 3 COO. 3H 2 O is made by dissolving a large amount of the solid into a few mL of water on a hot plate
Supersaturated Sodium Acetate A seed crystal is added to the flask…
Supersaturated Sodium Acetate Upon hitting the solution, it supplies a template for the solute to follow
Supersaturated Sodium Acetate Five pieces must come together in just the right pattern… Na + CH 3 COO 3 H 2 O NaCH 3 COO 3H 2 O(s) Sodium acetate trihydrate
Supersaturated Sodium Acetate The solution rapidly crystallizes outward from the seed locations
In going from a “liquid” state to a solid state, the H fus is released as heat!
Supersaturated Sodium Acetate To redissolve the solid, put the H fus back in…
Concentrations of solutions: Molarity: Molality: Mole fraction: ppm, ppb: Mols solute / L solvent Mols solute / kg solvent Mols solute / mols total Part per million/billion…
Molarity: (unit of concentration) n n Definition: Mols/Liter (M) Example: 4.0 g of NaOH dissolves into 1L What is the molarity of the solution? n Convert to moles n Calculate moles/liter 4.0g 1 mol/40g = 0.1 mol 0.1 mol/L = 0.10 M
Molarity Problems: n Instead of “grams of sample”… given: molarity of aqueous sample! n You must also be given the volume… X Why? n No converting grams into moles… multiply Molarity volume = moles
Molarity Examples: n Given: 27.52 mL of 0.1003 M NaOH How many moles of NaOH? u Units analysis: 0.02752 L × 0.1003 mol/L = 2.760e -3 mol Practice!!!
Molality Examples: n n 20.0 g of zinc(II) chloride is dissolved in a 250 mL volumetric flask, and water is added to the mark. n n Calculate the molality of chloride anions What to do first?
n Translate words & write equations: ZnCl 2 (s) → Zn 2+ (aq) + 2Cl (aq) n Convert grams into moles: Molar mass (ZnCl 2 ) = 136.3 g/mol 20.0g / 136.3 g/mol = 0.147 mol ZnCl 2 n Divide moles into kg of solvent: 0.147 mol / 0.250 kg = 0.588 m ZnCl 2
What is the molality of Cl ions? 0.588 m 2 mol Cl (aq) /1 mol ZnCl 2 ZnCl 2 = 1.18 m Cl Must be able to work both directions: What mass of NaCl is needed to make a 100 mL solution of 0.50 M NaCl? = 2.92 g NaCl
Aqueous Properties: Like dissolves like…. Polar species dissolve in polar solvents Non-polar species dissolve in non-polar solvents e.g. Which of the following would most likely dissolve in benzene? (A) H 2 O (B) CH 3 COOH (C) C 3 H 8 (D) C 6 H 5 NH 2 (A) H 2 O (B) CH 3 COOH (C) C 3 H 8 (D) C 6 H 5 NH 2
Hydrophobic Hydrophilic Other definitions: Water-fearing Water-loving