1. Intro to Solutions and Factors Affecting Solubility Mrs. Wilson
Friday 4-08 and Mon 4-11
Intro to Solutions and Factors Affecting Solubility
Mrs. Wilson

2. Objectives
Understand basic concepts of solutions and solvation.
Explain how changes in pressure and changes in temperature affect the solubility of solid and gaseous solutes.
Explain how agitation and surface area changes affect the rate of dissolution of solutes in solution.
Homework: 6.2 Homework on pg. 30; Daily Quiz next class.

3. Let’s get some whiteboards and markers out.
Daily Quiz Review
Let’s get some whiteboards and markers out.

6. Question 1
List ALL the IMFs (intermolecular forces) present between two molecules of glucose, C6H12O6.

7. Question 1 answer
List ALL the IMFs (intermolecular forces) present between two molecules of glucose, C6H12O6. LDF, dipole-dipole, AND H-bonding

8. Question 2
List the predominant (most important) IMF existing between two molecules of HI.

9. Question 2 answer
List the predominant (most important) IMF existing between two molecules of HI. Dipole-dipole forces. (HI is polar; has permanent dipoles.)

10. Question 3
Which has a higher melting point, CH4 or C4H10? Explain in terms of intermolecular forces.

11. Question 3
Which has a higher melting point, CH4 or C4H10? Explain in terms of intermolecular forces. Both are nonpolar but C4H10 contains more electrons. It is more polarizable. Its temporary dipoles are stronger than in CH4. Stronger attractions mean more energy must be added to make the molecules move.

12. Glucose, C6H12O6, is a solid, but C6H12 is a gas. Explain why.
Question 4
Glucose, C6H12O6, is a solid, but C6H12 is a gas. Explain why.

13. Question 4 Answer
Glucose has mainly H-bonds, but C6H12 is nonpolar and has mainly LDFs. H-bonds involve very strong permanent dipoles so Coulombic attraction between them is very strong. Stronger attractions make the molecules stay still and form a solid. C6H12 has weaker C. attractions formed by temporary weak dipoles. The weaker attractions mean the molecules are further apart.

14. Question 5
Why does iodine have a higher melting point than ice? Iodine = I2 Ice = H2O

15. Question 5 Answer
Iodine has more electrons than ice does – iodine is more polarizable and its e. clouds distort more. LDF’s are weaker than H-bonds but there are a lot of LDF’s in a sample of iodine. These forces add up to be more in iodine than in ice. The C. attractions in iodine add up to be stronger than in ice, so more energy must be absorbed to make the molecules move past each other.

16. Please put the markers and whiteboards back.
Daily Quiz
Please put the markers and whiteboards back.

17. Engage/Explore: Lab - Sugar Dissolving Race
In teams, see which solvent – water, alcohol, mineral oil, or vinegar will dissolve one sugar cube in the fastest period of time.
You may not heat the solvents.
Please wash and scrub the beakers out with soap and dry them with paper towel.

18. Explain: Intro to Solutions
Solutions are…
Homogeneous mixtures (so, can be separated through physical changes)
Made up of at least two parts: solute and solvent
If the solvent is water, the solution is aqueous
Gases, liquids OR solids
(examples: cheese, bread, shaving cream, fog, alloys)
Dissolution = dissolving

19. Explain: Intro to Solutions
When liquid solutes attempt to dissolve in liquid solvents, they are…
Miscible (can mix)
or immiscible (don’t mix)
Solvents (and solutes) can be…
Hydrophillic (water-loving = polar) or
Hydrophobic (water-hating = nonpolar)

20. Solvation
Hydration = solvation when the solvent is water

21. Solvation Animation
“Dissolution of Salt in Water”

22. 6.1 Review pg 7

23. 6.1 Review pg 7
Water has a bent molecular structure and permanent dipoles due to its highly electronegative H-O bonds. It is polar.
The partial + hydrogen ends attract the chloride anion away from the sodium cation. Those hydrogen ends face the chloride.
The partial – oxygen ends attract the sodium cation away from the chloride anion. The oxygen ends face the sodium.

24. Enthalpy of solvation = energy involved in solvation
It’s All About Energy
Enthalpy of solvation = energy involved in solvation

25. Solubility of Sugar in 100 g water
NOT the same as “rate of dissolution”
Solubility
The solubility of a substance is the maximum mass of material that will dissolve in a given amount of solvent at a given temperature to produce a stable solution.
Temperature
Solubility of Sugar in 100 g water
20°C
179 g
Close to 100°C
487 g

26. Factors Affecting Solubility
Nature of solute and solvent
Polar solutes dissolve in polar solvents
Nonpolar solutes dissolve in nonpolar solvents
(nonpolar = long HC chains, oil, gasoline)
“Like dissolves like”… why?

27. It’s All About Energy (yes… again)
Endothermic (solute absorbs energy to separate the molecules)
It’s All About Energy (yes… again)
Endothermic (solvent absorbs energy to separate the molecules)
Exothermic (to form solute-solvent IMFs, energy is released)
Bottom line… how much energy does it cost to do solvation? If the IMFs are all similar, there is sufficient energy available to be released and form the solution.

28. Factors Affecting Solubility
2. Pressure For gases: increase P, increase the solubility value More P = forces the gas molecules into the solution and dissolve
Nucleation = dissolved carbon dioxide clings onto the surface of the Mentos and comes out of solution to form bubbles… the bubbles build on top of each other and when the bubbles get big enough…

29. Factors Affecting Solubility
3. Temperature
For solids: increase T, increase the solubility value
More T = more kinetic energy available to help solute- solvent IMFs form = more mass of solid solute dissolves
(actually not true for ALL solids but for most of them)
For gases: decrease T, increase the solubility value
More T = more KE available BUT most gases are nonpolar = gases become more energetic and escape the solvent

30. Factors Affecting Rate of Dissolution
Increasing the surface area (aka: crush the solute)
More solvent molecules can surround solute if its surface area is larger.
Agitation (aka: stirring)
This brings fresh solvent into contact with solute.
Neither of these affects the mass of solute you can dissolve… only the speed with which you can dissolve.

31. Quiz Quiz Trade Review
You get a card, you get a card, everyone gets a card!
Walk around, partner up with one other person.
Take turns. Ask the other person the question that is printed on your card. Check their answer. Coach them if they didn’t know.
Switch roles.
Switch cards!
Move on to the next person 