14 March 2011

1. 14 March 2011 • Take Out: predicting products packet from last week to hand in, determining the identity of the pollutant lab, pencil • Do-Now: pre-lab on handout • Objective: SWBAT describe colligative properties and predict their effect on the properties of a solution. • Agenda: Making ice cream! Notes on colligative properties • Homework: finish ice cream lab handout

2. New unit – applications of solutions chemistry • Fresh start • Fun!

3. Ice Cream lab! • Need 2 volunteers to help measure, etc. • Pick a partner you would like to work with, sit with them at a lab table • If you don’t want ice cream, don’t pick a partner!

4. How does it work? The ice cream mixture has lots of dissolved solutes, so it won’t melt unless it is well below 0oC. Ice has to absorb heat energy in order to melt. Where does that heat energy come from? Adding salt lowers the melting point of the ice, so it must absorb even more heat energy (from the ice cream mixture) to melt. This makes the ice/water/salt solution even colder than plain ice water. The super cold solution brings the temp of the ice cream mixture to below freezing, to freeze the ice cream. Heat Energy

5. Ice cream lab! • If you follow instructions very carefully, this is the most delicious lab you will ever do! • STATION 1 – ingredients for part 1 • Door side first • STATION 2 – materials for part 2 • Windows side first • TEMP STATIONS – along windows • Hold the probe in the water for 10 sec

6. Dissolution of an ionic compound • What happens when a soluble ionic compound (like NaCl) is added to water? • http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.swf

7. Properties of solutions • The physical properties of a solution are different from the properties of the pure solvent used to make the solution • For example, salt water conducts electricity but pure water doesn’t!

8. Colligative Properties of Solutions • Colligative properties: properties of a solution that depend on the number of particles of solute (not the identity of the solute).

9. Freezing Point Depression • Freezing point is the temperature at which a solvent goes from a liquid to a solid. • With the addition of a solute, the freezing point decreases. • For example: • Freezing point of water is 0oC. • Freezing point of a 1.0 M NaCl solution is -2oC!

10. Why? • Attraction between water molecules and dissolved ions (like Na+) interferes with the formation of bonds to make a solid.

11. Key Question • How can we use freezing point depression to our advantage? • Examples: • Road salt • Ice cream!

12. http://www.kgw.com/news/local/What-is-De-Icing-made-out-of-116860568.htmlhttp://www.kgw.com/news/local/What-is-De-Icing-made-out-of-116860568.html

14. 15 March 2011 • Take Out: ice cream lab handout to check, notebook, pencil/pen • Do-Now: survey • Objective: SWBAT describe colligative properties and predict their effect on the properties of a solution. • Agenda: notes on colligative properties and introduction to acids and bases • Homework: none – good luck tonight!

15. Boiling Point Elevation • Boiling point is the temperature at which a solvent goes from liquid to gas. • With the addition of a solute, boiling point increases.

16. Dissolution of an ionic compound • What happens when a soluble ionic compound (like NaCl) is added to water? • http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.swf

17. Boiling Point Elevation Demo • Which will have the highest boiling point? • Pure water • 2 M NaCl solution • 2 M CaCl2 solution • Let’s try it! • We’ll use a temperature probe to collect and graph temperature over time.

18. Boiling Point Elevation • For example: • Boiling point of pure water: 100oC • Boiling point of 5.0 M NaCl solution: 103oC.

19. Why? • Attraction between water molecules and dissolved ions (like Na+) holds the water molecules together and prevents them from escaping into a vapor.

20. Introduction to Acids and Bases

21. Properties of Acids • Have a tart/sour taste • are corrosive (they eat away at other substances)

22. Properties of bases • Taste bitter • are slippery

23. pH • pH is a measurement of how acidic/basic a solution is • 0-14 scale • 0 is most acidic • 14 is most basic • 7 is neutral (water)

25. 16 March 2011 • Take Out: ice cream lab handout to check • Do-Now: order the following items from lowest pH to highest pH • Water • Lemonade • Toothpaste • Draino • Battery acid

26. 16 March 2011 • Objective: SWBAT describe the characteristics of acids and bases and understand the pH scale. • Agenda: notes on acids and bases, mini lab with pH of common substances • Homework: none!

27. pH • The numbers on the pH scale come from the hydrogen ion concentration [H+] • The higher the hydrogen ion concentration, the LOWER the pH! • Hydrogen ions are responsible for the corrosive properties of acids

29. Hydrogen ion concentration • [H+] increases by 10 for each step you go down on the pH scale

30. Linear Scale • Linear scale – y value changes at a constant rate with changes in the x value (straight line on a graph) • Example: The salary for a government employee changes by a set amount each year

31. Linear Scale

32. Logarithmic scale • Logarithmic scale – y value increases by being multiplied by 10 (curved line) • The pH scale is a logarithmic scale • Example: A solution with a pH of 6 is 10 times more acidic than a pH of 7 – it has 10 times more hydrogen ions in it

33. Earthquake! • Richter scale – 1-10 based on magnitude of the earthquake • So two magnitude 5’s should add up to a 10, right? (according to a CA politician…) • Only if it is linear (which it isn’t!) • A category 6 is 10 times stronger than a category 5, so you need 10 5’s to make the same energy as a 6 • So a 9 is 100,000 times stronger than a 5!!

34. pH • Use pH test paper to find the pH of each of the liquids in your plate. • Milk or milk of magnesium? • Vinegar or tap water? • Coke or coffee? • Write down which is which and how the [H+] compares between the two

36. Do-Now – Explain how the [H+] will differ between these different substances

37. 16 March 2011 • Objective: SWBAT describe the difference between strong and weak acids. • Agenda: clicker questions, notes and demo on strong vs. weak acids • Homework: acid rain article and questions

38. Clickers ready!

39. Acids are typically • Bitter tasting • Sour tasting • Slippery • All of the above

40. Bases can be • Bitter tasting • Slippery • Corrosive • All of the above

41. An example of a base is - • Lemon juice • Vinegar • Milk of magnesium • Your stomach juices

42. Battery acid is VERY corrosive. Which of the following would be its likely pH? • 14 • 9 • 4 • 1

43. Ocean water is slightly more basic than pure water. What would be its pH? • 12 • 8 • 6 • 3

44. Solutions with lower pH’s have ______ Hydrogen ions in them • More • Less • The same amount

45. A scale where the y value increases by a factor of 10 is called • Linear • Exponential • Quadratic • logarithmic

46. How would the [H+] of Lemon juice (pH=2) compare with tomato (pH=4) • Lemon juice has twice as many hydrogen ions • Lemon juice has half as many hydrogen ions • Lemon juice has 100 times more hydrogen ions • Lemon juice has 100 times fewer hydrogen ions

47. Strong vs. Weak Acids and Bases • A strong acid will dissociate (dissolve) completely in water. • HCl(aq) → H+(aq) + Cl-(aq) • At the end, only H+ and Cl- ions exist. • There are no HCl molecules left!

48. A weak acid will not dissociate completely in water. This is shown with a reversible arrow. • HF(aq) ⇄ H+(aq) + F-(aq) • At the end, there are some H+ and F- ions and also some HF molecules!

49. Strength of acids vs. concentration of acids • A concentrated acid isn’t necessarily a strong acid • Ex: 0.01 M HCl (a strong acid, but a very low concentration) • Ex: 16 M CH3COOH (a weak acid, but at a very high concentration.)

50. Strong vs. Weak Acid pH