1. Solutions Investigation 8

2. Part 1 - Mixtures

3. What is a Mixture? G:\ISTCS\School papers\Science\8th grade\Chemical Interactions\Media\Mixtures.wmv

4. Mixture – a combination of two or more substances.  Examples –  Solids – Mystery Mixture  Liquids - salad dressing  Gases – Air  Or any other combination

5. Preparing Mixtures – lab book p. 74

6. Discuss  What happened when you made a mixture of calcium carbonate and water?  What happened when you made a mixture of sodium chloride and water?

7. Solution  When you made a mixture of calcium carbonate and water, the calcium carbonate powder remained visible. The water was cloudy, and after a short time, the carbonate settled to the bottom of the cup. You could always see where the calcium carbonate was.

8. Solution  The sodium chloride went into the water and soon became invisible. You couldn't see where it was. It seemed to disappear, but it really didn’t go away.

9. Solution  When two substances are mixed, and it looks like one disappears into the other, the substances form a solution. The process is called dissolving. When salt is mixed in water, the salt dissolves in the water forming a solution.

10. Solution  A solution has 2 parts – the solute and the solvent.  The solute is the substance that dissolves (the salt), and the solvent is the substance in which the solute dissolves (the water).

11. Separating Mixtures  2 things are true about mixtures:  They can be made by putting substances together  They can be separated into their original substances.  How can we separate the 2 mixtures?  What method can we use to separate the calcium carbonate/water mixture into its two substances?  What method can we use to separate sodium chloride/water mixture into its two substances?

12. Filtering Mixtures – lab book p. 75 SLOWLY – Start with the Sodium/Chloride solution first

13. Discuss Results  Were you able to separate the two mixtures?  What happened when you tried to separate the sodium chloride from the water in the salt solution?  Why do you think the filter paper separated the calcium carbonate from the water, but not the sodium chloride?  How might we separate the sodium chloride and water?  What happens during evaporation?

14. Evaporate Liquids  Place 10 drop samples of each substance in the assigned wells using pipettes.  DO NOT mix the pipettes.  Record the time and date the investigation started.  Move your trays to the back table after labeling them with your team members’ names.

15. Click icon to add picture Break Point- You will finish this investigation the next class period.

16. Evaporation Results  Use hand lenses to observe your results.  Did the water in well 1 evaporate?  What was left in well 1?  Did the water in well 5 evaporate?  What was left in well 5?  Did the water in well 9 evaporate?  What was left in well 9?  Were you able to separate the two mixtures? How? Describe the separation process for each mixture.

17. www.fossweb.com  Play Explore Dissolving Simulation several times.  Concentrate on the solute particles sometimes.  Concentrate on the solvent particles sometimes.  Go through the pages behind the INFO button.  On another sheet of paper, discuss and report what you observed. This is a written assignment that will be collected at the end of the period and graded.

18. Assignment  As a class read How Things Dissolve in the Resource Book.  Answer questions p. 77 lab book.  Turn in p. 77

19. Part 2 - Saturation

20. Review Dissolving  Does sodium chloride dissolve in water? How do you know?  What happens at the particle level when sodium chloride dissolves?  In part 1 you added 2 ml of salt to 30 g of water. The salt dissolved. What do you think would happen if you added another 2 ml of salt? Would it dissolve?  Is there a limit to the amount of a substance that will dissolve in a measure of water?  If so, is the amount of a substance that will dissolve in a measure of water the same for all substances?  Come up with a plan for answering these questions.

21. More Solute Plan  Put a measured volume of water in one of the bottles.  Put in salt. Cap the bottle and shake until all of the salt dissolves.  Add more salt by scoops until you have used all of the salt or solid salt accumulates in the bottom of the bottle.  Determine how much salt actually dissolved in the water.

22. Lab book p. 78

23. 8 minutes – plan your procedure in your table teams Must have approval to start

24. Hints  Make solutions in bottles with caps to prevent spilling. Shaking will speed up dissolving.  Use sticky notes to label the bottles. Stick them at the water level for reference later.  Two students take charge of the sodium chloride, and two take charge of the magnesium sulfate.  The dry funnel can be used to guide the salts efficiently into the bottle.  Dry the funnel with a bit of paper towel if it gets even a single drop of liquid on it.

25. Gather Data  How many scoops of sodium chloride did it take to saturate 30 ml of water?  How many scoops of magnesium sulfate did it take to saturate 30 ml of water?

26. Saturation  When you dissolve a solid substance in water until no more will dissolve, the solution is a saturated solution. If you continue to add solid material to a saturated solution, the solid will simply pile up on the bottom of the container.

27. Discussion  Did sodium chloride and magnesium sulfate dissolve in water? What is your evidence?  Were you able to make a saturated solution of sodium chloride? What is your evidence?  Were you able to make a saturated solution of magnesium sulfate? What is your evidence?  Did the amount of liquid in the bottles change? Why?  Did the amount of water in the bottles change?  Did it take the same amount of sodium chloride and magnesium sulfate to make a saturated solution in 30 ml of water?

28. How many grams of sodium chloride and how many grams of magnesium sulfate are needed to saturate 30 ml of water?  What is in the bottle?  30 ml(g) of water, an unknown mass of substance dissolved in the water, and an unknown mass of a substance that is not dissolved.

29. Solution  Filter out the undissolved material with a paper funnel (coffee filter).  The saturated solution passes through the filter.  Weigh the saturated solution and subtract the mass of the water (30 g). The difference is the mass of the dissolved substance.

30. Complete the Inquiry  Saturate the filter paper with water before filtering. This will prevent loss of solution due to absorption by the filter.  Transfer the label from the bottle to the cup just before filtering.  Weigh the empty cup and label before filtering.  Record all results in lab book p. 79.

31. Clean up  Discard paper filters  Pour solutions in waste container  Clean all cups, funnels and bottles.

32. Share Results  Are there results that could be considered outliers (results that differ greatly from the majority)?  What is the average amount of sodium chloride and magnesium sulfate that is needed to saturate 30 g of water?  Write your thoughts in the conclusion section of the lab book p. 79.

33. Particle Model  What happened when the first scoop of sodium chloride was added to the bottle of water?  What happened in the solution when solid salt began to accumulate at the bottom of the bottle?  Write your answers in the section labeled “Deeper Thoughts” lab book p. 79  Turn in when complete.

34. Assignment  Resource Book – How Things Dissolve  Lab book Questions p. 77  Response Sheet – Solutions lab book p. 81  Turn in when complete.

35. Part 3 - Concentration

36. Review Saturation  You made 2 saturated solutions, sodium chloride and magnesium sulfate. Which saturated solution had more solute dissolved in it?  How much magnesium sulfate was needed to saturate 30 ml of water?

37. Stock Solutions  I have 2 magnesium sulfate solutions. They are not saturated.  Solution 1 is made with 200 ml of water and 20 g of magnesium sulfate.  Solution 2 is made with 200 ml of water and 50 g of magnesium sulfate.  How are these 2 solutions the same and how are they different?

38. Concentration  When 2 solutions are made with the same amount of water(solvent), but different amounts of magnesium sulfate(solute), the solutions are different concentrations.  The solution with more solute is more concentrated.

39. Concentration – a ratio between the amount of solute and the amount of solvent in a solution

40.  If I weigh 40 ml samples of these 2 solutions, what do you think I will discover?  Will the masses of the 2 volumes of solution be equal, or will the mass of one 40 ml sample be greater than the other?

41. Demo  Measure 40 ml samples of the 2 solutions.  Weigh the 2 solutions.  Come up with a statement about the relationship between the mass and the concentration of the solutions.

42.  When equal volumes of solutions made with the same substances are weighed, the sample with the greatest mass is the most concentrated. Conversely, the sample with the lowest mass is the least concentrated. There is a direct relationship between mass and concentration.

43. Task  Each group will make their own solution with magnesium sulfate and water. After the solutions are made, we will investigate them to see if we can figure out which solution is the most concentrated.

44. Recipes – lab book p. 83  Each team gets an assigned recipe. Circle the number of the recipe you are assigned.  The recipe indicates the mass of the magnesium sulfate and the mass of water you should mix to make your solution.  Be patient and take turns at the scale.

45. Make Solutions  Measure the water accurately, using a graduated cylinder. Use a pipette to get the volume exact.  Measure the mass of the magnesium sulfate accurately. Zero the balance with the 250 ml cup on the pan.  Wear protective eyewear.  Mix and stir carefully.  Avoid spills.

46. Compare Solutions  Which of the solutions we made is more concentrated?  How would you find out?

47. Procedure  Every group will measure and weigh 10 ml of their samples.  Measure and record the mass of the samples.  Compare the masses of the samples.  Record the masses in column 4 of the table on the Magnesium Sulfate Solution Sheet. Title the column “Mass of 10 ml(g).”  Put your results on the master table, and transcribe other results to your table.

48. Mass of 10 ml Concentratio n

49. Discussion  Answer the first question on the sheet.  Concentration of solutions is most easily compared when concentration is expressed as mass per unit volume, that is, the mass (g) of 1 ml.  Calculate the concentration of the solutions in grams per milliliter by diving the mass of each sample by 10 ml.  Complete the last column on the chart.

50. Summary  A solution is a mixture of 2 (or more) substances. In a solution, one substance, the solute, is dissolved in the other substance, the solvent.  When a solute dissolves, it is broken into particles by solvent particles. The solute particles are carried in the solvent by solvent particles. The solute particles are evenly distributed throughout the particles of the solvent.

51. Summary  There is a limit to the amount of solute that can dissolve in a given amount of solvent. When the solvent has no more room for solute particles, the solution is saturated. Additional solute will remain undissolved on the bottom of the container.  The amount of solute dissolved in a volume of solvent determines the concentration of the solution. Concentration is a ratio of solute to solvent in a solution.

52. Summary  The substances in a solution are not changed chemically when they dissolve. Often evaporation will separate the solvent and the solute.

53. Click icon to add picture Break Point

54. Review Summary Concepts

55. Assignment  Read Concentration in your Resource Books.  Lab book p. 85 Concentration Questions.  Turn in p. 85

56. Midsummative Exam 8