Solubility

1. Solubility Init 4/2/2015 by Daniel R. Barnes WARNING: This presentation may contain images and other content taken from the world wide web, content whose owners have not given permission that they be disseminated and used. Do not copy, store, upload, post, e-mail, or otherwise distribute or keep this presentation. Its very existence may be illegal. It is intended to be viewed only by Mr. Barnes’ students, and only during a school year when they are taking chemistry with him.

2. Get out a pencil. You’re probably going to mapke some mistokes.

3. NGSS Justification of Lesson NGSS in boldface (Barnes’ justifications in italics) HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.(Sodium, from the left (group 1A), with one valence e-, loses 1 e- to become Na+. Chlorine, from the right (group 7A), with seven valence e-, gains 1 e- to become Cl-.) HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.(Sodium and chlorine, being a metal and a nonmetal, react to form sodium chloride. The sodium loses electrons, which chlorine gains. The positive sodium ions are attracted by ionic bonds to the negative chloride ions.) HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.(Sodium chloride is a robust solid at room temperature, with a strong crystal structure and a high melting point due to the powerful ionic bonding between its cations & anions. However, the polarity of the water molecule allows water molecules to dissolve salt, forming an aqueous solution of solvated ions.) HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs. (Salt will dissolve in water faster if the water is hot. Higher temperatures mean faster-moving particles, so ions are more likely to break free of their crystal lattice AND faster-wandering water molecules will arrive at the surface of salt crystals at a higher frequency and carry away solvated ions faster. Salt dissolving in water may not be a chemical reaction per se, but the principle of temperature speeding it up is very much akin to the principle that higher temperatures speed up chemical reactions.) HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. (The connection between this lesson and this standard is disturbingly similar to the connection to HS-PS1-3 . . . ) HS-PS3-2: Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motions of particles (objects) and energy associated with the relative positions of particles (objects). (Higher temperature salt water means faster-moving water molecules and more furiously-jiggling salt crystal ions. Ions in a salt crystal are at a relatively low level of potential energy relative to what they would have if they were separated  solidity.)

4. SWBAT. . . . . . explain why and how salt dissolves in water

5. HELPFUL HINT: Turn to page 451 (section 15.2)

6. IMPORTANT: As you draw on your “Salt Crystal DissolvingSkeleton Notes” worksheet, leave the right side of the sheet blank . . . until I say it’s okay to draw there.

7. Group leaders, on your whiteboards, write a brief description of what is pictured inside the square on your worksheet. Everyone, on your worksheets, use block letters to label what the thing in the square is supposed to be. On our worksheet, the salt crystal looks like a square. What shape is a salt crystal in real life? a cube SALT CRYSTAL

8. Erase the whiteboard and pass it to the next person. Next person, draw the nine circles found inside the square. Inside each circle, write the correct elemental symbol. Everyone, on your worksheets, label your sodium atoms and chorine atoms. Cl- Cl- Na+ Do not erase the whiteboard, but do pass it to the next person. That person should write the correct charges on each atom. Cl- Na+ Na+ Cl- Cl- Na+ Everyone, on your worksheets, write the pluses and minuses each ion has. SALT CRYSTAL

9. Pass the whiteboard to the next person. Next person, erase your whiteboard. Draw a picture of a water molecule and label each circle in the water molecule with the correct elemental symbol. Everyone, on your worksheets, label your hydrogen and oxygen atoms. O H H Cl- Cl- Na+ Cl- Na+ Na+ Cl- Cl- Na+ SALT CRYSTAL

10. Now, add the correct symbols to show the partial charges on the atoms in the water molecule. d- Everyone, on your worksheets, label your partial charges now. Also, at the very bottom of the worksheet, briefly explain what the d+ & d- symbols mean. O H H d+ d+ Cl- Cl- Na+ d+ = partial positive charge d- = partial negative charge Cl- Na+ Na+ Partial electric charges happen when two atoms form a polar covalent bond due to a moderate difference in electronegativity between the two atoms  unequal sharing of electrons  + & - atoms. Cl- Cl- Na+ SALT CRYSTAL

11. Everyone, on your worksheets, extend your salt crystals by adding more sodium and chloride ions until your squares are full. d- O H H d+ d+ Na+ Cl- Cl- Na+ Cl- Cl- Na+ Na+ Na+ Cl- Cl- Na+ Cl- Cl- Na+ Na+ SALT CRYSTAL

12. Pass the whiteboard to the next person in the group. Next person, erase the whiteboard. Draw a water molecule above a sodium ion, positioned correctly so that the water molecule and the sodium ion would attract each other. d+ d+ H H O d- d- O H H d+ d+ Na+ Cl- Cl- Na+ Cl- Everyone, on your worksheet, draw another water molecule, above a sodium ion on the top of the salt crystal, oriented so that the water molecule and the sodium ion would attract each other. Cl- Na+ Na+ Na+ Cl- Cl- Na+ Cl- Cl- Na+ Na+ SALT CRYSTAL

13. TPS: Discuss with your group what story is being told by our drawing. You have 47 seconds to discuss. d+ d+ H H O d- d- Water molecules wander randomly until they bump into the salt crystal. Salt ions on the outside of the crystal are attracted to the partial electric charges on the water molecules. Ions on the outside of the salt crystal are pulled off by water molecules, which then wander away with them. The salt crystal dissolves. O H H d+ d+ Na+ Cl- Cl- Na+ Cl- Cl- Na+ Na+ Na+ Cl- Cl- Na+ Cl- Cl- Na+ Na+ SALT CRYSTAL

14. Let’s animate the dissolving process, just in case our words haven’t done it justice . . . d+ d+ d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

15. Let’s animate the dissolving process, just in case our words haven’t done it justice . . . d+ d+ d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

16. d+ d+ d- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

17. d+ d+ d- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

18. d+ d+ d- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

19. d+ d+ d- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

20. d+ d+ d- Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

21. d+ d+ d- Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

22. d+ d+ d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

23. d+ d+ d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

24. d+ d+ d+ d+ d- d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

25. d+ d+ d+ d+ d- d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

26. d+ d+ d+ d+ d+ d+ d- d- d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

27. d+ d+ d+ d+ d+ d+ d- d- d- Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

28. Stirring with a spoon will sweep the dissolved salt ions out of the area, preventing salt ions from re-joining the crystal. Less re-joining  better crystal shrinkage [Sorry no animation for that yet . . . ] d+ d+ d+ d+ d- d- Cl- Na+ Na+ Cl- Cl- Na+ Na+ Cl- Cl- Na+ Na+

29. d+ d+ H H O d- Water molecule pulls chloride ion out & wanders away with it. Water molecule pulls sodium ion out & wanders away with it. d- We need to indicate in our drawing that water molecules are stealing ions from the crystal, so let’s draw some circles and arrows and explain what they mean. O H H d+ d+ Na+ Cl- Cl- Na+ Cl- Cl- Na+ Na+ Na+ Please draw loops & arrows on your worksheet to show how the water molecules are abducting salt ions. Also, write little explanations next to them. Cl- Cl- Na+ Cl- Cl- Na+ Na+ SALT CRYSTAL

30. Now we’re going to draw a salt solution on the right side of the paper. I hope you’ve been keeping it blank like I asked you to earlier.

31. d+ d+ d+ d+ d+ d+ d+ d+ d- d- d- d- Pass the whiteboard to the next person in the group. Next person, erase the whiteboard and draw a sodium ion surrounded by water molecules. Orient the water molecules so that they’d be attracted to the sodium ion. Na+ TPS 23 sec: What word describes a dissolved ion that is surrounded by water molecules? A: “solvated” Everyone, draw a “solvated” sodium ion in the upper half of the right side of your worksheet.

32. d+ d+ d+ d+ d+ d+ d+ d+ d- d- d- d- Pass the whiteboard to the next person in the group. Next person, erase the whiteboard and draw a chloride ion surrounded by water molecules. Orient the water molecules so that they’d be attracted to the chloride ion. Cl- Everyone, draw a “solvated” chloride ion in the lower half of the right side of your worksheet.

33. d+ d+ d+ d+ d+ d+ d+ d+ d+ d+ d+ d+ d+ d+ d- d- d- d- d- d- d- Na+ Cl- TPS 23 sec: What would you call the mixture of dissolved ions and water molecules on the right side of the page? SALT WATER SOLUTION

34. SWBAT. . . . . . list and explain factors that affect solubility.

35. Now that we know how a salt crystal dissolves . . . TPS 59 seconds: On your whiteboard, list some things that would help a salt crystal dissolve. . . . the clock is running . . . TIME’S UP. Show us what you wrote on your boards.

36. HELPING SALT CRYSTALS DISSOLVE Salt crystals dissolving requires water molecules to wander randomly so that they can bump into the outside surfaces of the salt crystals. Therefore, if the water is hotter, water molecules will wander faster and hit the salt crystal harder and more often. If the water is hotter, ions in salt crystals will jiggle more violently, making it easier for them to break away from their attractive ion neighbors. If the water is stirred, the salty water around a dissolving crystal will get replaced with fresh water, speeding the dissolving process by slowing the re-crystallization process.

37. HELPING SALT CRYSTALS DISSOLVE If the salt is ground into a fine powder, the increase in surface area will allow it to dissolve faster than if it were still made of large crystals. Since salt ions need to be solvated, there had better be plenty of water molecules to surround them. More solvent allows more solute to dissolve.

38. Okay. Now it’s time for a little quiz. Flip your worksheet over.

39. Prepare for the quiz . . . Group leaders, give everyone an answer document. Title = “Salt Dissolving Quiz” Don’t worry about the test number or the form. Do, however, write and bubble your ID# clearly.

40. Take the quiz. Your score on the quiz will not affect your grade, but finding out how you did will help you and me figure out what you know and what you don’t know. When you’re done, bring your answer document to the teacher’s desk so you can have it scanned. We’ll go over the questions when everybody is done. Until then, if you’re done with the quiz, answer the essay question on the back of your worksheet, below the multiple choice questions.

41. Okay. Let’s go over the quiz. I encourage you to take notes on the back of your worksheet as we discuss the answers.

42. 1. In a water molecule, the bond between a hydrogen atom and an oxygen atom is polar. This is why a. hydrogen atoms in a water molecule attract sodium ions b. oxygen atoms in a water molecule attract chloride ions c. there is a partial electric charge on each atom d. water and oil mix easily

43. 2. Which of the following makes it more difficult for a salt crystal to dissolve? a. higher temperatures b. re-crystallization c. stirring d. random molecular motion 2nd EASIEST QUESTION IN QUIZ

44. 3. Which of the following words means “becoming surrounded by water molecules”? a. crystallization b. solidification c. lattice formation d. solvation

45. 4. If the difference in electronegativity between hydrogen and oxygen were considerably bigger, a. the bond between hydrogen and oxygen would be nonpolar covalent. b. the bond between hydrogen and oxygen would be ionic. c. salt would be less soluble in water. d. oil would be more soluble in water. HARDEST QUESTION IN QUIZ

46. 5. Electrostatic forces are the main reason that salt ions can be carried away by water molecules. Electrostatic forces a. are always attractive and exist between any two particles that are made of matter. b. exist between charged objects. c. get weaker as two objects get closer to each other. d. depend only upon mass. 2nd HARDEST QUESTION IN QUIZ

47. 6. What makes molecules and other particles move faster? a. higher temperatures b. higher molar masses c. freezing d. differences in electronegativity EASIEST QUESTION IN QUIZ

48. Keep your answer document. There’s still room for three more quizzes on that answer document, so . . . Keep it somewhere in your binder where you’ll be able to find it easily the next time we do one of these end-of-lesson quizzes.

49. 4/9/2015 periods 2, 3, 4, 5, & 6