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Welcome to Chem 121-01

Welcome to Chem 121-01. HAPPY NEW YEAR !!! Pick up CAPA #1 - outside on shelf Pick up syllabus - in front Get your photo taken - get index card . Outline: 1/10/07. What to expect?. Plus ç a change: Plus la m ê me chose:.

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Welcome to Chem 121-01

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  1. Welcome to Chem 121-01 • HAPPY NEW YEAR !!! • Pick up CAPA #1 - outside on shelf • Pick up syllabus - in front • Get your photo taken - get index card

  2. Outline: 1/10/07 • What to expect? • Plus ça change: • Plus la même chose: • ACS standardized final (cumulative over two semesters) • CAPA, keypads, text & lectures… • Go over course syllabus

  3. Outline: 1/10/07 • Any questions? Do DISCUS post assignment… Read Chapter 12…try CAPA early…

  4. Outline: 1/10/07 • Any questions? • Start chapter 12 - Solutions Solution properties Colligative properties

  5. Solution: Solvent: Solute: Aqueous Solution: Homogenous mixture of 2 or more components Majority component of solution Minority component of solution Solvent is H2O, denoted as species (aq) Some Aqueous Properties:

  6. Types of solutions: • Table 12-1 (p.484)

  7. More Definitions • A solution holding the maximum solute is...saturated • A solution that can hold more solute is...unsaturated • A solution that is holding too much solute is...supersaturated

  8. Supersaturated Sodium Acetate A supersaturated solution of NaCH3COO.3H2O is made by dissolving a large amount of the solid into a few mL of water on a hot plate Demo

  9. Supersaturated Sodium Acetate A seed crystal is added to the flask…

  10. Supersaturated Sodium Acetate Upon hitting the solution, it supplies a template for the solute to follow

  11. Supersaturated Sodium Acetate Five pieces must come together in just the right pattern… Na+ CH3COO- 3 H2O NaCH3COO3H2O(s) Sodium acetate trihydrate

  12. Supersaturated Sodium Acetate The solution rapidly crystallizes outward from the seed locations

  13. Supersaturated Sodium Acetate

  14. Supersaturated Sodium Acetate In going from a “liquid” state to a solid state, the DHfus is released as heat!

  15. Supersaturated Sodium Acetate To redissolve the solid, put the DHfus back in… Demo

  16. Concentrations of solutions: Mols solute / L solvent • Molarity: • Molality: • Mole fraction: • ppm, ppb: Mols solute / kg solvent Mols solute / mols total Part per million/billion…

  17. Molarity: (unit of concentration) • Definition: Mols/Liter (M) • Example: 4.0 g of NaOH dissolves into 1L What is the molarity of the solution? • Convert to moles • Calculate moles/liter • 4.0g  1 mol/40g = 0.1 mol • 0.1 mol/L = 0.10 M

  18. Molarity Problems: • Instead of “grams of sample”… • given: molarity of aqueous sample! • You must also be given the volume… • Why? • No converting grams into moles… • multiply Molarityvolume = moles

  19. Units analysis: 0.02752 L × 0.1003 mol/L = 2.760e-3 mol Molarity Examples: • Given: 27.52 mL of 0.1003 M NaOH • How many moles of NaOH? Practice!!!

  20. Molality Examples: • 20.0 g of zinc(II) chloride is dissolved in a 250 mL volumetric flask, and water is added to the mark. • Calculate the molality of chloride anions • What to do first?

  21. Translate words & write equations: • ZnCl2(s)→ Zn2+(aq) + 2Cl-(aq) • Convert grams into moles: • Molar mass (ZnCl2) = 136.3 g/mol • 20.0g / 136.3 g/mol = 0.147 mol ZnCl2 • Divide moles into kg of solvent: • 0.147 mol / 0.250 kg = 0.588 m ZnCl2

  22. What is the molality of Cl- ions? 0.588 m 2 mol Cl-(aq) /1 mol ZnCl2 ZnCl2 Must be able to work both directions: What mass of NaCl is needed to make a 100 mL solution of 0.50 M NaCl? = 1.18 m Cl- =2.92 g NaCl

  23. 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) H2O (B) CH3COOH (C) C3H8 (D) C6H5NH2 (A) H2O (B) CH3COOH (C) C3H8 (D) C6H5NH2

  24. Other definitions: Hydrophobic Hydrophilic Water-fearing Water-loving

  25. Hydrophobic p.108

  26. Other definitions: Hydrophobic Hydrophilic Biochemical terms (p.510) Monolayer Micelle Vesicle

  27. p.108 Like dissolves like….

  28. Surfactants: • Anything which alters behavior of solute-solvent mixture….(e.g. soap) Applications? NaCl in cooking Road salt for ice Antifreeze Saline drips Gatorade

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