Essential Question: What makes water unique compared to other substances? Do Now: Explain why do you think water is important for life? HW: Water properties worksheet Binder check Wednesday

Properties of Water Cohesive nature of water Ability to moderate temperature Unusual phase changes Versatile solvent http://www.thewaterfallpractice.co.uk/assets/images/waterfall_ireland_pdphoto.jpg

THE PROPERTIES OF WATER 1. Cohesion of Water Water is a polar molecule, electrons are shared unequally Cohesion is the ability of water molecules to attach to other water molecules Attach by hydrogen bonds http://www.nsf.gov/news/special_reports/water/images/cp_photo.jpg

In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen This makes the oxygen end of the molecule slightly negatively charged The hydrogen end of the molecule is slightly positively charged Water is therefore a polar molecule (–) (–) O H H (+) (+) Figure 2.9

H+ atom is covalently bonded to the oxygen via a shared pair of electrons. Oxygen is an "electronegative" or electron "loving" atom compared with hydrogen "polar" molecule, meaning that there is an uneven distribution of electrons This attraction forms weak bonds called hydrogen bonds

Surface Tension The cohesion of water molecules at the surface of a body of water Due to hydrogen bonding, water molecules can move from a plant’s roots to its leaves Insects can walk on water due to surface tension created by cohesive water molecules

Adhesion Water can also be attracted to other materials. http://farm1.static.flickr.com/200/480451566_e66f7cc4f3.jpg?v=0 http://en.wikivisual.com/images/9/96/Water_drops_on_spider_web.jpg Water can also be attracted to other materials.

Capillary Action When one water molecule moves closer to the straw molecules the other water molecules also move up into the straw. Water Mercury

Water’s hydrogen bonds moderate temperature Water has high specific heat Specific heat = heat needed to raise temp. of 1g of substance by 1ºC Boiling Point High .... water stays liquid longer water can moderate Earth’s global temperature able to absorb a great deal of heat energy without a large increase in temperature As water cools, a slight drop in temperature releases a large amount of heat http://bio.winona.msus.edu/berg/IMAGES/earth_from_space.jpg

Unusual Phase Change Gas Liquid Solid Like no other common substance, water exists in nature in all three physical states: as a liquid as a gas as a solid Gas Liquid Solid

Hydrogen bonds are stable Hydrogen bonds constantly break and re-form Density of Water Ice is Less Dense than Liquid Water Molecules in ice are farther apart than those in liquid water Water is densest at 4°C. Hydrogen bond ICE Hydrogen bonds are stable LIQUID WATER Hydrogen bonds constantly break and re-form BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

Water is a Versatile Solvent Also known as the “Universal solvent”. Polar substances are enveloped by hydration spheres. “Like dissolves like!”

Solutions and Suspensions Two types of mixtures can be made with water Solutions All the components of a solution are evenly distributed throughout the solution. In a salt–water solution, table salt is the solute—the substance that is dissolved. Water is the solvent—the substance in which the solute dissolves

Solutions and Suspensions Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out. The movement of water molecules keeps the small particles suspended. Suspension of flour in water http://www.answers.com/topic/mixture

Acids, Bases, and pH Acids, Bases, and pH A water molecule can react to form hydrogen and hydroxide ions. H20  H+ + OH- Water is neutral because the number of positive hydrogen ions (H+) produced is equal to the number of negative hydroxide ions (OH-) produced.

Acids, Bases, and pH The pH scale Measurement system to indicate the concentration of H+ ions in solution. The pH scale ranges from 0 to 14. Solution pH range H+/OH- ratio Acid 0-6.999 concentration of H+ ions greater than OH- ions Neutral 7.0 concentration of H+ ions and OH- ions is equal. Base 7.001-14 concentration of H+ ions less than OH- ions

Acids, Bases, and pH Acids Any compound that forms H+ ions in solution.  Contain higher concentrations of H+ ions than pure water Strong acids tend to have pH values that range from 1 to 3. The hydrochloric acid produced by the stomach to help digest food is a strong acid. BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

Acids, Bases, and pH Bases A base is a compound that removes H+ ions from a solution.  Basic, or alkaline, solutions contain lower concentrations of H+ ions than pure water Strong bases, such as lye, tend to have pH values ranging from 11 to 14. BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

(Higher concentration of H+) (Lower concentration of H+) pH scale Acidic solution Neutral solution Basic solution (Higher concentration of H+) Increasingly ACIDIC (Lower concentration of H+) Increasingly BASIC NEUTRAL [H+] = [OH–] Lemon juice; gastric juice Grapefruit juice Tomato juice Urine PURE WATER Seawater Milk of magnesia Household ammonia Household bleach Oven cleaner Human blood H+ OH– The pH scale Each pH unit represents a tenfold change in concentration of H+ BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

Cabbage juice pH paper phenolphthalein pH Indicators -turns pink in presence of base http://www.bio-world.com/images/061036.jpg http://ull.chemistry.uakron.edu/organic_lab/distribution/dist13.gif

Acids, Bases, and pH Buffers The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5. If the pH is lower or higher, it will affect the chemical reactions that take place within the cells. enzymes denature & reactions stop (That’s a bad thing!) http://diverge.hunter.cuny.edu/~weigang/Images/05-06_denaturation_1.jpg

Connection: Acid precipitation threatens the environment Some ecosystems are threatened by acid precipitation Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003.

Properties of Water A molecule in which the charges are unevenly distributed is called a polar molecule. cohesive molecule. hydrogen molecule. covalent molecule.

Properties of Water 2 Hydrogen bonds between water molecules result from adhesion between water molecules. magnetic attractions between water molecules. uneven electron distribution in each water molecule. ionic bonds in the water molecule.

Acids, Bases, and pH 1 A dissolved substance is called a solvent. solution. solute. suspension.

Acids, Bases, and pH 2 A compound that removes ions from a solution is called a(an) base. buffer. acid. salt.

Acids, Bases, and pH 3 On a pH scale, a value of 2 means that the solution has equal concentrations of H+ and OH- ions. the same concentration of H+ ions as pure water. higher concentration of H+ than in pure water. lower concentration of H+ than in pure water.

Acids, Bases, and pH 4 Tomato juice has a pH of 4, while soap has a pH of 10. How much more acidic is the juice? 6 times more acidic 1,000,000 times more acidic 60 times more acidic 1,000 times more acidic