L I D E. Chapter 12 The Liquids and Solids Around Us: Especially Water. No Gravity, No Spills. Liquids and Solids. Chemistry in Focus 3rd edition Tro

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1 Chemistry in Focus rd edition Tro Chapter The iquids and olids Around Us: specially Water No Gravity, No pills 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. pills would not spread over surfaces, as on arth iquids and solids are held together by cohesive forces. Without these forces all matter would be gaseous. iquids and olids

2 ach 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. vaporation 5 6 Crystalline olids olids 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. n solids, molecules move less allowing them to interact more. 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.

3 7 n 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. f not for cohesive forces among molecules, all matter would be gaseous. 9 ispersion (ondon) Forces The weakest cohesive force Present among all atoms and molecules Result from instances when electrons are not distributed evenly in the molecule or atom

4 0 For chemically similar elements or compounds, the magnitude of dispersion forces is generally proportional to the molar mass of the molecule or atom. Relative Boiling Points 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. ipole Forces

5 5 Consequently, polar molecules have higher boiling points than nonpolar ones even given similar molecular weight. ike issolves ike A polar substance will not mix with a nonpolar substance. oap serves as a molecular liason between the two.

6 6 7 8 Hydrogen Bonding A cohesive attraction between polar molecules containing hydrogen bonded to either fluorine, oxygen, or nitrogen leading to higher than expected boiling points. melling 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.

7 9 0 Volatility iquids that vaporize easily have a high vapor pressure. Volatile Weaker cohesive forces More endothermic iquids that do not vaporize easily have a low vapor pressure. Nonvolatile tronger cohesive forces ess endothermic ince perfumes have different components, their odors change through the day. Chemists Have olutions A solution is defined as a homogeneous mixture of two or more substances. olvent: the majority component olute: the minority component Concentration An expression of the amount of solute relative to the amount of solvent xpressions of Concentration Percent by mass Percent by volume Molarity the number of moles of solute divided by the number of liters of solution

8 Other Concentration Units Parts per million (ppm) Another Concentration Unit Milligrams per liter

9 5 6 7 No other compound of similar molar mass comes close to the high boiling point of water. Wherever there is water, there is life. WATR Unique tructure Highly polar Two O-H bonds that hydrogen bond to other water molecules xpands when it freezes ce is less dense than liquid water and will float. ce on bodies of water insulates the marine life beneath. Unique Properties 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.

10 8 9 0 Water: Where is it and how did it get there? Only a tiny fraction of arth s water is usable in lakes and streams (0.0%). The oceans hold 97.%, and.6% is in ice caps, glaciers, and ground water. and water comes from oceans through the hydrologic cycle. Water: Pure or Polluted? Virtually no water is pure; it can only be made in a laboratory. ike most liquids, water is a mixture containing a number of different elements and compounds. ome components are harmful and some beneficial.

11 Hard Water As water runs through soils rich in limestone, calcium and magnesium ions dissolve into it. uch hard water has no adverse health effects, but scaly deposits on pipes, fixtures, utensils form. Hard water decreases the effectiveness of soap. bathtub ring ofteners are charged with sodium ions that exchange place with calcium and magnesium. odium increases the risk of high blood pressure. Water oftening

12 5 6 Biological Contaminants 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. Chemical Contaminants umping of wastes by industry into streams and rivers umping of industrial waste into the atmosphere through emissions Pesticides and fertilizers are significant contaminants and end up in drinking water supplies. Organic Contaminants Volatile Benzene, carbon tetrachloride, others Nonvolatile thylbenzene, chlorobenzene, TC Both types come from fertilizers, gasoline, pesticides, paints, and solvents. They increase cancer risk, liver and kidney damage, and CN damage.

13 7 8 9 norganic Contaminants Asbestos from natural and man-made supplies Nitrates immediate danger to humans iminish hemoglobin s ability to carry oxygen Blue baby syndrome Metals mercury, lead Kidney and CN damage Radioactive Contaminants More common in areas rich in uranium deposits Uranium, radium, and radon all come primarily from natural sources. ngestion increases cancer risk.

14 0 The afe rinking Water Act 97 et maximum contaminant levels (MCs) Public water suppliers sample and test water. Responsible for notifying government agencies and YOU of violations PA requires water suppliers to actively prevent contamination during transport between treatment and your tap. Public Water Treatment To meet PA requirements, providers purify and treat water before delivery. 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

15 5 Home Water Treatment PA 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. ome groups disagree and recommend removal of compounds overlooked by local water providers. Carbon Filtration Particularly effective in removing organic contaminants and chlorine Water oftening Most common home treatment Hard water is passed through a zeolite. An ion-exchange material with a rigid cagelike molecular structure that can hold metal ions. odium ions exchange with magnesium and calcium. Zeolite is recharged by flushing with concentrated sodium chloride

16 6 7 8 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. esalination 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. n reverse osmosis, pressure is applied to the salt water side of the semipermeable membrane, forcing the production of fresh, desalinated, water. Tap water can be purified this way. esalination plants can produce fresh water from seawater on a large scale.