Wednesday March 30 , 2011

1. WednesdayMarch 30, 2011 (??)

2. Bell RingerWednesday, 3-30-11 When energy is added to a liquid, what phase change occurs? vaporization – either evaporation or boiling How much stronger is an acid at pH 4 than one at pH 6? 102 = 100 x

3. Announcements If you have not yet taken our last test (Test 8), please see me ASAP! We will have a test this Friday.

5. Continue Worksheet Review of Important TAKS Concepts (Part 1)

6. Start 4

7. Reading a Graph How many centimeters did these plants grow in 15 days with a 10% phosphorus fertilizer? Which % fertilizer would be the most economical for this farmer to use? Why?

8. Start 1, 3

9. Reading a Graph At what volume would the pressure of nitrogen gas be 350 kPa? What happens to the pressure of nitrogen gas as the volume increases?

10. Analyzing a Graph Horses kept in stables sometimes chew on wood. This can lead to damage to the mouth and digestive system. The graph shows the results of a study of a medication that prevents horses from chewing on wood. From the graph, what inference can be made about the effectiveness of the product? A. Most horses like the medication. B. The medication is most effective between Days 4 and 5. C. Most horses will show improvement within 7 days. D. The effects of the medication are long lasting.

11. Analyzing a Graph Horses kept in stables sometimes chew on wood. This can lead to damage to the mouth and digestive system. The graph shows the results of a study of a medication that prevents horses from chewing on wood. From the graph, what inference can be made about the effectiveness of the product? A. Most horses like the medication. B. The medication is most effective between Days 4 and 5. C. Most horses will show improvement within 7 days. D. The effects of the medication are long lasting.

12. TAKS Sample Question Which of these is an advantage of producing electricity using solar power plants rather than using coal-fired power plants? A. Solar power plants can operate for about 10 hours per day. B. Solar power plants can produce variable amounts of energy. C. Solar power plants produce fewer pollutants. D. Solar power plants require continuous sunlight.

13. Stop 3

14. TAKS Sample Question Which set of coefficients balances the equation? F. 3, 3, 1, 2 G. 6, 1, 1, 3 H. 3, 2, 1, 6 J. 6, 2, 1, 6

15. Stop 4

16. TAKS Sample Question The transfer of heat by the movement of air currents in Earth’s atmosphere is an example of — A. conduction B. convection C. radiation D. fusion

17. Stop 1

18. TAKS Sample Question In photography, which of these is an example of a chemical change? F. Light being refracted by a camera lens G. Adjusting a lens to focus light H. Halide granules being activated by light J. Allowing a certain wavelength of light into the camera

19. TAKS Sample Question Silver bromide is a type of halide. Elements from which group in the periodic table are necessary to form halide compounds? A. Group 4 B. Group 5 C. Group 10 D. Group 17

20. Solutes: Electrolytes and Nonelectrolytes • Substances that dissolve in water are classified according to whether they yield molecules or ions in solution. • When an ionic compound dissolves, the positive and negative ions separate from each other and are surrounded by water molecules. • These solute ions are free to move, making it possible for an electric current to pass through the solution. • A substance that dissolves in water to give a solution that conducts electric current is called an electrolyte.

21. Solutes: Electrolytes and Nonelectrolytes • Sodium chloride, NaCl, is an electrolyte, as is any soluble ionic compound. • Certain highly polar molecular compounds, such as hydrogen chloride, HCl, are also electrolytes because HCl molecules form the ions H3O+ and Cl− when dissolved in water. • By contrast, a solution containing neutral solute molecules does not conduct electric current because it does not contain mobile charged particles.

22. Solutes: Electrolytes and Nonelectrolytes A substance that dissolves in water to give a solution that does not conduct an electric current is called a non-electrolyte. Sugar is a non-electrolyte. The picture below shows an apparatus for testing the conductivity of solutions.

23. Solutes: Electrolytes and Nonelectrolytes The electrodes are conductors that are attached to a power supply and that make electric contact with the test solution. For a current to pass through the light-bulb filament, the test solution must provide a conducting path between the two electrodes.

24. Solutes: Electrolytes and Nonelectrolytes A non-conducting solution is like an open switch between the electrodes, and there is no current in the circuit. The light bulb glows brightly if a solution that is a good conductor is tested. Such solutions contain solutes that are electrolytes.

25. Solutes: Electrolytes and Nonelectrolytes For a moderately conductive solution, however, the light bulb is dim. If a solution is a poor conductor, the light bulb does not glow at all. Such solutions contain solutes that are non-electrolytes.

26. Lab Electrolytes and Non-Electrolytes

27. Bell Ringer3-8-10 Why does saltwater conduct electrical current but sugar water does not?

28. Bell Ringer3-8-10 Saltwater conducts electrical current because water breaks the salt into charged ions, which conduct current. Sugar is broken down into molecules, which do not conduct current.

29. Concentration of Solutions • The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution. • Some medications are solutions of drugs - a one-teaspoon dose at the correct concentration might cure the patient, while the same dose in the wrong concentration might kill the patient. • The way of expressing the concentrations of solutions is molarity

30. Concentration of Solutions • Sometimes solutions are referred to as dilute or concentrated. • Dilute just means that there is a relatively small amount of solute in a solvent. • Concentrated means that there is a relatively large amount of solute in a solvent. • Note that these terms are unrelated to the degree to which a solution is saturated – a saturated solution of a substance that is not very soluble might be very dilute.

31. Molarity • Molarity is the number of moles of solute in one liter of solution. • The symbol for molarity is M. • To find the molarity of a solution, you must know the molar mass of the solute.

32. Molarity • Ex) a “one-molar” solution of sodium hydroxide, NaOH, contains one mole of NaOH in every liter of solution. • The concentration of a one-molar solution of sodium hydroxide is written as 1 M NaOH. • One mole of NaOH has a mass of 40.0 g - if this quantity of NaOH is dissolved in enough water to make exactly 1.00 L of solution, the solution is a 1 M solution. • If 20.0 g of NaOH, which is 0.500 mol, is dissolved in enough water to make 1.00 L of solution, a 0.500 M NaOH solution is produced.

33. Molarity • This relationship between molarity, moles, and volume may be expressed in the following way:

34. Molarity • If twice the molar mass of NaOH, 80.0 g, is dissolved in enough water to make 1 L of solution, a 2M solution is produced. • The molarity of any solution can be calculated by dividing the number of moles of solute by the number of liters of solution. • Note that a 1 M solution is not made by adding 1 mol of solute to 1 L of solvent.

35. Molarity • In such a case, the final total volume of the solution would not be 1 L. • Instead, 1 mol of solute is first dissolved in less than 1 L of solvent, then the resulting solution is carefully diluted with more solvent to bring the total volume to 1 L.

36. Molarity Sample Problem #1 You have 3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that solution? Sample Problem #2 You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain?

37. Lab Super-Saturated Solutions (page 107)

38. Bell Ringer3-10-10 What is a super-saturated solution?

39. Bell Ringer3-10-10 A super-saturated solution is one that has more solute dissolved in it than it should have at that temperature.

40. Review for Test 9 Mixtures: Solutions, Colloids, and Suspensions Solubility Electrolytes and Non-Electrolytes Molarity (page 109)

41. 1 What type of mixture contains the smallest solute particles? solutions What type of mixture contains the largest solute particles? suspensions

42. 2 A student has an unknown sample of a mixture, and she wants to determine which type of mixture it is. She shines a light though the mixture and see a glow inside the container. She filters the mixture but finds no particles trapped in the filter. There is no sediment on the bottom of the container. What is most likely the identity of the mixture? a colloid

43. 3 A chemistry student wants to determine the identity of a mixture. He observes that the mixture is clear and colorless, has no smell, and conducts an electric current. What is most likely the identity of this mixture? a salt water solution

44. 4 If a student determines that a mixture will not conduct an electric current, what would be the best description of the solute used to make the mixture? A non-electrolyte

45. 5 If a solvent breaks a solute all the way down into ions, what will certainly be a property of the mixture? The mixture will conduct electrical current.

46. 6 List three properties that a solution of sugar-water will have and one property it will not have. will have: a sweet taste, be fluid in nature, and be mostly odorless will not have: electrical conductivity

47. 7 List two examples of each of the following: elements hydrogen, oxygen compounds water, table salt homogeneous mixtures saltwater, sugar water milk, pond water heterogeneous mixture alloys steel, brass

48. 8 If a student is trying to determine the saturation point of a solid solute in a liquid solvent, what factors would he most be concerned with? the nature (identity) of the solute and solvent and the temperature of the solvent.

49. 9 What is true concerning dissolving and crystallization when the saturation point of a solute in a solvent has been reached? dissolution equals crystallization

50. 10 A student finds that the rate of crystallization is equal to the rate of dissolution in her mixture. As a result of this, what has her mixture reached? solution equilibrium