What else do you know about water? • How does the molecule look? • How does it function? • What can it do in our everyday lives? The Extraordinary Properties of Water Learning Objectives • Understand the nature of the water molecule and its unique properties and how these are altered by the presence of salt in solution. Water • In case you missed yesterday: • A water molecule (H2O), is made up of three atoms --one oxygen and two hydrogen. H H O Water is Polar • In each water molecule, the oxygen atom attracts more than its "fair share" of electrons • The oxygen end “acts” negative • The hydrogen end “acts” positive • Causes the water to be POLAR • However, Water is neutral (equal number of e- and p+) --- Zero Net Charge Hydrogen Bonds Exist Between Water Molecules • Formed between a highly Electronegative atom of a polar molecule and a Hydrogen • One hydrogen bond is weak , but many hydrogen bonds are strong Interaction Between Water Molecules Negative Oxygen end of one water molecule is attracted to the Positive Hydrogen end of another water molecule to form a HYDROGEN BOND What are the Properties of Water? Water’s Physical Properties • Water is unique in that it is the only natural substance that is found in all three states -- liquid, solid (ice), and gas (steam) -- at the temperatures normally found on Earth. Water’s Physical Properties • Water's freezing and boiling points are the baseline with which temperature is measured: 0o on the Celsius scale is water's freezing point, and 100o is water's boiling point. Do you think the boiling point remains the same at higher elevations? Properties of Water • Cohesion Properties of Water • Cohesion • Adhesion Properties of Water • Cohesion • Adhesion • High Specific Heat Properties of Water • Cohesion • Adhesion • High Specific Heat • High Heat of Vaporization Properties of Water • Cohesion • Adhesion • High Specific Heat • High Heat of Vaporization • Less Dense as a Solid Cohesion • Attraction between particles of the same substance ( why water is attracted to itself) • Results in Surface tension (a measure of the strength of water’s surface) • Produces a surface film on water that allows insects to walk on the surface of water Cohesion & Surface Tension Helps insects walk across water Cohesion • What will happen when water molecules come in contact with each other? • Grab a dropper from the middle of your table, use proper technique to fill it with the blue-colored water. • Lay out a sheet of wax paper. Slowly begin adding drops of the water to the wax paper (spread out the drops). • What will happen when you move the drops around with the toothpick? Try it. • Floating paper clip made of steel with copper plating. The high surface tension helps the paper clip - with much higher density - float on the water Compare the Surface Tension of Water to other liquids Materials: • • • • • • • Paper towel Tray Penny Water Alcohol Vinegar Soap water Compare the Surface Tension of Water to other liquids Before you begin, make a prediction: How many drops of water will fit on the penny before it overflows? Adhesion • Attraction between two different substances. • Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and blood in the body. Water on a String • Materials (for 1 table): 1. 2 plastic cups (1 half way filled with water) 2. Long piece of cotton string 3. Tape Water on a String • Think about the properties of water we have talked about so far. What do you predict will happen? Water on a String • Instructions: 1. Dunk all but an inch of your string in water. 2. Tape the dry part of the string inside the empty cup. 3. Hold the other end of the string inside the water-filled cup with your finger. 4. Pour SLOWLY Capillary Action • Water molecules will “tow” each other along. It is the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension. • Example: transpiration process which plants absorb water from the soil; it moves through the plant to evaporate from leaves. Adhesion Causes Capillary Action Which gives water the ability to “climb” structures You can see capillary action in action (although slowly) by doing an experiment where you place the bottom of a celery stalk in a glass of water with food coloring and watch for the movement of the color to the top leaves of the celery. Adhesion Also Causes Water to … Form spheres & hold onto plant leaves Attach to a silken spider web Surface Active Agents • In cleaning, surface tension must be reduced so water can spread and wet surfaces. • Chemicals that are able to do this effectively are called surface active agents, or surfactants. They are said to make water "wetter." Surfactants • Surfactants perform other important functions in cleaning: – loosening, emulsifying (dispersing in water) – holding soil in suspension until it can be rinsed away • Surfactants can also provide alkalinity, which is useful in removing acidic soils. Surfactants in “Action” • Materials (for 3-4 people/1 table): 1. 2. 3. 4. Tray with water 2 Index cards Scissors Cup with dish soap Surfactants in “Action” • Put one index card on top of the water at one end of the tray. • What happens? Surfactants in “Action” • Cut a small triangle out of one end of the index card (less than an inch) • Use the tip of your finger to add a SMALL amount of soap to the inside EDGES of the triangle/ the V notch (don’t put too much!) • Place the index card at one end of the tray. • What happens? Why? High Specific Heat • Amount of heat needed to raise or lower 1g of a substance 1° C. • Water resists temperature change, both for heating and cooling. IT’S A HEAT SINK! The Ocean acts as a tremendous heat sink to moderate the earth's temperature. • Water can absorb or release large amounts of heat energy with little change in actual temperature. High Specific Heat • Water has a high specific heat index. This means that water can absorb a lot of heat before it begins to get hot. – This is why water is valuable to industries and in your car's radiator as a coolant. High Heat of Vaporization • Amount of energy to convert 1g of a substance from a liquid to a gas • In order for water to evaporate, hydrogen bonds must be broken. • As water evaporates, it removes a lot of heat. High Heat of Vaporization • Water's heat of vaporization is 540 cal/g. • In order for water to evaporate, each gram must GAIN 540 calories (temperature doesn’t change --100oC). • As water evaporates, it removes a lot of heat with it (cooling effect). • Water vapor forms a kind of global ‘‘blanket” which helps to keep the Earth warm. • Heat radiated from the sunwarmed surface of the earth is absorbed and held by the vapor. Morning Do 9-11-15 Objective: TLW demonstrate the basic principles of fluid dynamics by determining which has a greater density -- fresh or salt water, warm or cold water. 1. What two properties of water play a part in capillary action? 2. What must break in order for water to evaporate? Water is Less Dense as a Solid • Ice is less dense as a solid than as a liquid (ice floats) • Liquid water has hydrogen bonds that are constantly being broken and reformed. • Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances. Water is Less Dense as a Solid •Which is ice and which is water? Water is Less Dense as a Solid Water Ice Temperature & Salinity affect Density of Water • Complete lab activity in your group • You will need to assign tasks: – 1 Reader (you will read ALL instructions on lab) – 1 Recorder (you will record all of the information on your lab sheet) – 1-2 Doers (you will be collecting materials and performing procedures) Density • Cold, salty water is more dense than warm, fresh water and will sink below the less dense layer. – Density is defined as the measure of a material's mass (e.g. grams) divided by its volume (e.g. milliliters). • Mixing of seawater influences the density of seawater thereby affecting ocean circulation. Density of Water • High density in cold, salty waters –why is this important? – Big Idea • Two of the most important characteristics of ocean water are its temperature and salinity. Together they help govern the density of seawater, which is a major factor controlling the ocean's vertical movements and layered circulation. Homeostasis • Ability to maintain a steady state despite changing conditions • Water is important to this process because: a. Makes a good insulator b. Resists temperature change c. Universal solvent d. Coolant e. Ice protects against temperature extremes (insulates frozen lakes) Solutions & Suspensions • Water is usually part of a mixture. • There are two types of mixtures: – Solutions – Suspensions Solution • Ionic compounds disperse as ions in water • Evenly distributed • SOLUTE – Substance that is being dissolved • SOLVENT – Substance into which the solute dissolves Solution Suspensions • Substances that don’t dissolve but separate into tiny pieces. • Water keeps the pieces suspended so they don’t settle out. Turbidity • The amount of particulate matter that is suspended in water. • Material that causes water to be turbid include: clay, silt, plankton, organic and inorganic matter, & microscopic organisms. • Turbidity is measured by shining a light through the water and is reported in nephelometric turbidity units (NTU). Acids, Bases and pH One water molecule in 550 million naturally dissociates into a Hydrogen Ion (H+) and a Hydroxide Ion (OH-) H2O H+ Hydrogen Ion Acid + OH - Hydroxide Ion Base The pH Scale • Indicates the concentration of H+ ions • Ranges from 0 – 14 • pH of 7 is neutral • pH 0 up to 7 is acid … H+ • pH above 7 – 14 is basic… OH• Each pH unit represents a factor of 10X change in concentration • pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6 Acids • Strong Acids have a pH of 1-3 • Produce lots of H+ ions Bases • Strong Bases have a pH of 11 to 14 • Contain lots of OHions and fewer H+ ions The pH Scale Buffers • Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization). • Produced naturally by the body to maintain homeostasis Weak Acid Weak Base