Chapter 12 The Liquids and Solids Around Us: Especially Water

1. Chapter 12 The Liquids and Solids Around Us: Especially Water

2. No Gravity, No Spills • Undisturbed by air and gravity, liquids take the shape of a sphere. • The geometrical shape of lowest surface area to volume ratio is the sphere. • Spills would not spread over surfaces, as on Earth • Liquids and solids are held together by cohesive forces. • Without these forces all matter would be gaseous.

3. Liquids and Solids

4. Each molecule within a liquid is attracted to its neighbors, but thermal energy keeps it moving in a random path. At the surface, there are fewer other molecules with which to interact. Evaporation

5. Solids in which the arrangement of molecules or atoms is well-ordered; each molecule or atom vibrates but its average position remains fixed in the crystalline structure. In solids, molecules move less allowing them to interact more. Crystalline Solids

6. Melting and Boiling • Thermal energy competes with cohesive forces to determine the phase of a substance. • At the melting point, thermal energy in a solid overcomes the forces of attraction between molecules. • At the boiling point, thermal energy in a liquid overcomes the forces of attraction between molecules.

7. In the cases of both melting and boiling, no chemical bonds within the molecules have been broken. • Temperatures required to break chemical bonds are frequently MUCH higher. • The strength of cohesive forces is related to the molecule’s structure.

8. Forces That Hold Us Together • The major cohesive forces in order of increasing strength are dispersion, dipole, and hydrogen bonding. • If not for cohesive forces among molecules, all matter would be gaseous.

9. The weakest cohesive force Present among all atoms and molecules Result from instances when electrons are not distributed evenly in the molecule or atom Dispersion (London) Forces

10. For chemically similar elements or compounds, the magnitude of dispersion forces is generally proportional to the molar mass of the molecule or atom.

11. Relative Boiling Points

12. Present in polar molecules that have permanent dipoles Molecules align such that positive ends of dipoles interact with the negative ends of neighboring dipoles. Polar bonds may or may not geometrically cancel within a molecule. Dipole Forces

13. Consequently, polar molecules have higher boiling points than nonpolar ones even given similar molecular weight.

14. Like Dissolves Like • A polar substance will not mix with a nonpolar substance. • Soap serves as a molecular liason between the two.

16. Hydrogen Bonding • A cohesive attraction between polar molecules containing hydrogen bonded to either fluorine, oxygen, or nitrogen leading to higher than expected boiling points.

18. Smelling Molecules • Perfume is a mixture of molecules with a range of cohesive forces. • The molecules with the weakest cohesive forces are the ones you smell first.

19. Volatility • Liquids that vaporize easily have a high vapor pressure. • Volatile • Weaker cohesive forces • More endothermic • Liquids that do not vaporize easily have a low vapor pressure. • Nonvolatile • Stronger cohesive forces • Less endothermic • Since perfumes have different components, their odors change through the day.

20. Chemists Have Solutions • A solution is defined as a homogeneous mixture of two or more substances. • Solvent: the majority component • Solute: the minority component • Concentration • An expression of the amount of solute relative to the amount of solvent

21. Expressions of Concentration • Percent by mass • Percent by volume • Molarity – the number of moles of solute divided by the number of liters of solution

23. Other Concentration Units • Parts per million (ppm)

24. Another Concentration Unit • Milligrams per liter

25. No other compound of similar molar mass comes close to the high boiling point of water. Wherever there is water, there is life. WATER

26. Unique Structure • Highly polar • Two O-H bonds that hydrogen bond to other water molecules • Expands when it freezes • Ice is less dense than liquid water and will float. • Ice on bodies of water insulates the marine life beneath.

27. Cells in biological tissue are damaged when frozen due to the expansion of water on freezing. Water dissolves many organic and inorganic compounds and is responsible for the flow of nutrients in the body. Unique Properties

28. Water:Where is it and how did it get there? • Only a tiny fraction of Earth’s water is usable in lakes and streams (0.014%). • The oceans hold 97.4%, and 2.6% is in ice caps, glaciers, and ground water. • Land water comes from oceans through the hydrologic cycle.

30. Water: Pure or Polluted? • Virtually no water is pure; it can only be made in a laboratory. • Like most liquids, water is a mixture containing a number of different elements and compounds. • Some components are harmful and some beneficial.

31. Hard Water • As water runs through soils rich in limestone, calcium and magnesium ions dissolve into it. • Such hard water has no adverse health effects, but scaly deposits on pipes, fixtures, utensils form. • Hard water decreases the effectiveness of soap. • bathtub ring

32. Softeners are charged with sodium ions that exchange place with calcium and magnesium. Sodium increases the risk of high blood pressure. Water Softening

34. Microorganisms that cause diseases like hepatitis, cholera, typhoid, and dysentery come from the dumping of human and animal waste into the ground or nearest river. Biological Contaminants

35. Chemical Contaminants • Dumping of wastes by industry into streams and rivers • Dumping of industrial waste into the atmosphere through emissions • Pesticides and fertilizers are significant contaminants and end up in drinking water supplies.

36. Organic Contaminants • Volatile • Benzene, carbon tetrachloride, others • Nonvolatile • Ethylbenzene, chlorobenzene, TCE • Both types come from fertilizers, gasoline, pesticides, paints, and solvents. • They increase cancer risk, liver and kidney damage, and CNS damage.

37. Inorganic Contaminants • Asbestos – from natural and man-made supplies • Nitrates – immediate danger to humans • Diminish hemoglobin’s ability to carry oxygen • Blue baby syndrome • Metals – mercury, lead • Kidney and CNS damage

38. Radioactive Contaminants • More common in areas rich in uranium deposits • Uranium, radium, and radon all come primarily from natural sources. • Ingestion increases cancer risk.

40. The Safe Drinking Water Act • 1974 • Set maximum contaminant levels (MCLs) • Public water suppliers sample and test water. • Responsible for notifying government agencies and YOU of violations • EPA requires water suppliers to actively prevent contamination during transport between treatment and your tap.

41. Public Water Treatment • To meet EPA requirements, providers purify and treat water before delivery.

42. Additional Treatments • Kill biological contaminants with ozone or UV light. • These do not offer protection after water leaves the treatment facility. • Adjustment to neutral pH • Addition of fluoride to aid in the prevention of tooth decay

43. Home Water Treatment • EPA considers drinking water from a public provider to be adequately treated for the protection of health. • But homeowners may desire treatment for hardness, clarity, and taste. • Some groups disagree and recommend removal of compounds overlooked by local water providers.

44. Carbon Filtration • Particularly effective in removing organic contaminants and chlorine

45. Water Softening • Most common home treatment • Hard water is passed through a zeolite. • An ion-exchange material with a rigid cage-like molecular structure that can hold metal ions. • Sodium ions exchange with magnesium and calcium. • Zeolite is recharged by flushing with concentrated sodium chloride

46. Reverse Osmosis • This process is the reverse of a naturally occurring one in which water flows from an area of low solute (salt) concentration to high solute concentration.

47. Desalination • A semipermeable membrane allows water to pass through it but blocks other substances. • The side containing the salt water will rise as fresh water flows into it. • In reverse osmosis, pressure is applied to the salt water side of the semipermeable membrane, forcing the production of fresh, desalinated, water.

48. Tap water can be purified this way. • Desalination plants can produce fresh water from seawater on a large scale.

49. Mole/Volume Concentration: Molarity Molarity (M)- mole-based concentration unit, defined by the number of moles of solute per liter of solution (use final solution volume) M = moles of solute L solution

50. Calculating molarity from moles Calculate the molarity of 3.0 L of solution containing 3.4 mol NaCl.