1. Chapter 7 How Molecules Mix
Lecture Presentation
Chapter 7 How Molecules Mix
Bradley Sieve
Northern Kentucky University
Highland Heights, KY

2. 7.1 Four Different Types of Dipole Attractions
Electron unevenly distributed in a molecule
Extreme cases are present in ionic compounds
Water exhibits a weaker dipole type called a polar molecule

3. 7.1 Four Different Types of Dipole Attractions
Molecular Attractions Involving Dipoles

4. 7.1 Four Different Types of Dipole Attractions
Ion-Dipole Attractions
Interaction between ionic charge and molecular dipole

5. 7.1 Four Different Types of Dipole Attractions
Collective attraction from many molecules

6. 7.1 Four Different Types of Dipole Attractions
Induced Dipole Attractions
Dipole induced in a nonpolar molecule by surrounding dipole containing molecules

7. Concept Check
How does the electron distribution in an oxygen molecule change when the hydrogen side of a water molecule is nearby?

8. Concept Check
Because the hydrogen side of the water molecule is slightly positive, the electrons in the oxygen molecule are pulled toward the water molecule, inducing in the oxygen molecule a temporary dipole in which the larger side is nearer the water molecule (rather than as far away as possible)

9. 7.1 Four Different Types of Dipole Attractions
Dipole–Induced Dipole Attractions
Interaction between a permanent dipole and a dipole–induced dipole
Weaker than dipole–dipole attractions

10. Concept Check
Distinguish between a dipole–dipole attraction and a dipole–induced dipole attraction.

11. Concept Check
The dipole–dipole attraction is stronger and involves two permanent dipoles. The dipole–induced dipole attraction is weaker and involves both a permanent and temporary dipole.

12. 7.1 Four Different Types of Dipole Attractions
Induced dipole–induced dipole attractions
Temporary dipoles are due to the momentary arrangement of electrons
Temporary dipoles can induce dipoles on other nonpolar molecules
Has largest effect in the largest atoms and molecules
Also called dispersion forces

13. 7.1 Four Different Types of Dipole Attractions

14. 7.1 Four Different Types of Dipole Attractions

15. Concept Check
Distinguish between a dipole–induced dipole attraction and an induced dipole–induced dipole attraction.

16. Concept Check
The dipole–induced dipole attraction is stronger and involves both a permanent and temporary dipole. The induced dipole–induced dipole attraction is weaker and involves two temporary dipoles.

17. 7.1 Four Different Types of Dipole Attractions

18. 7.1 Four Different Types of Dipole Attractions

19. Concept Check
Methanol, CH3OH, which can be used as a fuel, is not much larger than methane, CH4, but it is a liquid at room temperature. Suggest why.
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20. Concept Check
The polar oxygen–hydrogen covalent bond in each methanol molecule leads to hydrogen bonding between molecules. These relatively strong interparticle attractions hold methanol molecules together as a liquid at room temperature.

21. 7.2 A Solution Is a Single-Phase Homogeneous Mixture
Homogenous mixture of a single phase
Examples:
Sugar dissolved in water is a liquid solution
Gemstones are solid solutions
Alloys are solid solutions
Air is a gaseous solution

22. 7.2 A Solution Is a Single-Phase Homogeneous Mixture

23. 7.2 A Solution Is a Single-Phase Homogeneous Mixture
Parts of a solution
Solvent is the largest component of a solution
Solute makes up the other components
Sugar dissolved in water solution
Water is the solvent
Sugar is the solute

24. Concept Check
What is the solvent in the gaseous solution we call air?

25. Concept Check
Nitrogen is the solvent, because it is the component present in the greatest quantity.

26. 7.2 A Solution Is a Single-Phase Homogeneous Mixture
Types of solutions based on solute amount
Saturated solution
No more solute will dissolve in the solution
Unsaturated solution
Less solute present than will dissolve in the solution

27. 7.3 Concentration Is Given as Moles per Liter
The amount of solute dissolved per amount of solvent

28. 7.3 Concentration Is Given as Moles per Liter
Chemical amount of a substance
Equal to 6.02 × 10−23 particles

29. 7.3 Concentration Is Given as Moles per Liter
Molarity
Common unit of concentration
Number of moles per liter of solution

30. Concept Check
How many moles of sucrose are in 0.5 liter of a 2-molar solution? How many molecules of sucrose is this?

31. Concept Check
You need to understand that 2-molar means 2 moles of sucrose per liter of solution. To obtain the amount of solute, you should multiply solution concentration by amount of solution:
(2 moles/L)(0.5 L) = 1 mole,
which is the same as 6.02 × 1023 molecules.

32. 7.4 Solubility Is How Well a Solute Dissolves
Ability of a solute to dissolve in a solvent
If there is any appreciable amount, it is considered soluble
Depends on number and types of interactions

33. 7.4 Solubility Is How Well a Solute Dissolves
Types of Solubility
Infinitely soluble
No practical point of saturation
Insoluble
Solute does not dissolve in solvent to any appreciable extent

34. 7.4 Solubility Is How Well a Solute Dissolves
Temperature Effects on Solubility
Solubility increases with temperature due to increased kinetic energies
Solid that forms upon cooling is called a precipitate

35. 7.4 Solubility Is How Well a Solute Dissolves
Solubility of gases
Gas solubility decreases with increased temperature
Due to the increased kinetic energy and the solute molecules escaping the solution

36. 7.4 Solubility Is How Well a Solute Dissolves

37. 7.5 Soap Works by Being Both Polar and Nonpolar
Contains both polar and nonpolar ends
Can interact with both polar and nonpolar grime
Michelle forms to carry grime away in water

38. 7.5 Soap Works by Being Both Polar and Nonpolar
Soap is produced by the reaction of fats with NaOH
Chemists create synthetic soaps called detergents

39. 7.6 Softening Hard Water Hard Water
Water containing large amounts of Ca and Mg
Can form solid compounds, clogging pipes
Leads to soap scum by binding the soap molecules
Treatments include
Addition of Na2CO3 to soap
Water-softening system

40. 7.6 Softening Hard Water
Na2CO3 Treatment

41. 7.6 Softening Hard Water
Water-Softening Unit

42. 7.7 Purifying the Water We Drink
Purifying drinking water
Utilizes physical properties or water and solutes
Creating potable (drinkable) water is a several-step process

43. 7.7 Purifying the Water We Drink
Fresh water can be made from salt water
Desalination is the removal of salt from water
Primary methods include
Distillation, which utilizes vaporization of the water
Reverse osmosis, which passes water through a semipermeable membrane

44. 7.7 Purifying the Water We Drink
Home Distillation

45. 7.7 Purifying the Water We Drink
Reverse Osmosis
external pressures push the water

46. 7.7 Purifying the Water We Drink
Bottled water
More expensive than tap water
Discarded water bottles are a large source of waste
Often simply purified tap water from municipal sources