1 Chemical and Physical Properties of Water Unit 1

1. What are some processes your body needs water for? 2. What type of bond holds the H 2 to the O in water? 3. What type of bond holds individual water molecules together? 4. When an atom gains or loses an electron, it is called an ___. 2

3  Water is essential to ALL life on earth!  Without water, life as we know it would not exist  Water is the most abundant compound in living things. Most organisms are %water  Water is used to transport materials (blood, sap), regulate temperature, and to produce cell products like saliva, tears, sweat, stomach acids, etc. ☺

4  Water can also be used to provide support and structure to body parts (jellyfish) and for movement (hydraulic systems such as those found in worms and starfish) ☺

5 Chemistry of Water  Water is forms molecules by 2 hydrogen atoms that are bonded to a single oxygen atom: H 2 O.  Molecules are formed when elements are combined by covalent bonds.  The oxygen and hydrogen atoms are held together because they “share” electrons ☺

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7  These “shared electrons” form a covalent bond  The water molecule has a shape like a widened “V” ☺

8  Because the oxygen atom is much larger than the hydrogen atoms, it tends to “share” the electrons a little more than the hydrogen atoms do  The unequal sharing of the electrons causes water to have a slight electrical charge on each end ☺

9  The oxygen end is negative, and the hydrogen end is positive  Polar molecule – has an electrical charge on each end; water is a polar molecule  Because water is polar, it can dissolve many substances.  It is considered to be the universal solvent.☺

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11 Hydrogen Bonds  The slight electrical charges on each end of a water molecule helps to attract other molecules, and gives water many of its unique properties ☺

12  The slight bonds that form between the negative end of one water molecule and the positive end of another water molecule are called hydrogen bonds ☺

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16  Cohesiveness – attraction between water molecules; causes water molecules to stick together  Viscosity –due to cohesion between water molecules; property by which water tends to resist objects entering the water (surface tension)☺

17  Example: belly flop, bugs that walk on water ☺  Jesus Lizzard

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21  Adhesiveness – causes water to stick to other materials  The adhesive properties of water cause capillary action-tendency of water to creep up this tubes. This is how plants rooks take in water, and the meniscus is formed in a glass graduated cylinder.  Both cohesiveness and adhesiveness are due to the hydrogen bonds that form between water molecules and between water molecules and other substances ☺

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23  Solvent – substance that dissolves other substances. Water is an excellent solvent because of its hydrogen bonds  Ions and other polar substances such as sugar are easily dissolved by water ☺

24  Two oppositely charged ions attract each other and form very powerful bonds: ionic bonds  Na + + Cl - Na + Cl -  (reactants) (products)  Sodium (positive ion) plus chlorine (negative ion) forms sodium chloride (table salt)  Na + Cl Na + Cl Na + Cl  Ionic Bond Ionic Bond Ionic Bond  NaCl Ionic Bond NaCl Ionic Bond NaCl Ionic Bond

25  The bonds formed by these electrical charges are easily broken by the polar water molecules; that is why salt dissolves in water.  When salt is dissolved in water it forms a solution because all of the particles are evenly distributed. ☺

26  Gases such as oxygen, carbon dioxide, and nitrogen are also easily dissolved into water  Oxygen is essential for most organisms, and the amount of carbon dioxide dissolved in the water affects the pH of the water  Soft drinks  Global Warming Makes Ocean Acidic ☺

27 Physical Properties of Water  On earth, water exists in 3 physical states 1. Solid – ice – below 32°F, 0°C 2. Liquid – water – between 32°F - 212°F 0°C - 100°C 0°C - 100°C 3. Gas – vapor – above 212°F, 100°C ☺

28  Temperature is a measure of the amount of kinetic energy in a substance  Kinetic energy refers to how much the atoms in a substance are “bouncing around”  A Thermometer is a molecular speedometer.☺

29  As the kinetic energy increases, the distance between the molecules increases and the temperature goes up (expands)  As the kinetic energy decreases, the distance between molecules decreases and the temperature goes down (shrinks) ☺

30  Density – describes the distance between molecules in a substance  Often expressed as Mass/Volume ☺

31  Generally, the lower the temperature, the greater the density  Water is unique because its density- temperature relationship does not follow normal rules at low temperatures  Water breaks away from “normal” behavior at about 4°C (36°F) ☺

32  At that temperature and lower, water actually becomes slightly less dense  This is due to the way that water molecules “line up” as the water molecules begin to repel each other as they come very close together  This is the reason that ice floats; it is actually less dense than liquid water ☺

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34  If water behaved like “normal” substances, lakes and oceans would freeze from the bottom up (because the denser cold water would sink)  Life as we know it would not exist, as most of the earth’s water would remain frozen most of the year ☺

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38  In the winter time, the bottom of a frozen lake will have a layer of water that is around 36°F.  Since water is most dense at this temperature, this prevents all but the most shallow of lakes and ponds from freezing solid ☺

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40 Temperature & Density in Solutions  Since the distance between molecules increases as the temperature increases, warmer water can hold more dissolved substances than colder water  Example: hot water can dissolve more salt than cold water ☺

41  One exception to this general rule deals with dissolved gases  As the temperature of the water (along with its dissolved oxygen) increases, the kinetic energy of the oxygen molecules increases ☺

42  Oxygen molecules near the surface “bounce out” into the atmosphere  The water molecules don’t “bounce out” as quickly as the oxygen molecules because of cohesion ☺

43  Oxygen molecules diffuse from deeper water to replace those that escape near the surface, where they also heat up and “bounce out”  This causes the entire water mass to lose oxygen when the temperature rises ☺

44  This loss of oxygen in warm/hot water affects all organisms that live in the water  Example: catfish ponds in the summer often suffer from low oxygen levels ( put oxygen back into the water)  Organisms that are not adapted to these condition can die out rapidly ☺

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46  Even though hot water is capable of holding more oxygen than cold water, cold water usually has more dissolved oxygen than hot water ☺

47 Salinity  Salinity refers to the amount of salt dissolved in water.  Freshwater differs from saltwater due to the amount of dissolved salt present ☺

48  All water has some dissolved salt present  Most of the salt is sodium chloride (table salt), but trace amounts of other salts, such as magnesium chloride, are also present  Salt enters the oceans from run-off (rivers bring it from the land) ☺

49  Salinity is usually measured in parts per thousand (‰)  Example: 14 parts =14 ‰ = 1.4% salt  This seawater would contain 98.6% water and 1.4% salt ☺

50  Salinity in the oceans is NOT uniform  Areas near rivers may have much lower salinity than areas of the open ocean far away from land  Normal ocean salinity runs from ‰ to as low as 1 ‰ in estuaries (where rivers meet the ocean)  Name some salty lakes.☺

51  Some landlocked lakes are also salty  The Great Salt Lake in Utah - 23 ‰  The Dead Sea ‰  Salinity in the ocean is slowly increasing as more salt is washed in from rivers ☺

 No river drains the Dead Sea.  Swimming in the Dead Sea Swimming in the Dead Sea Swimming in the Dead Sea 52

53  As the salinity of water increases, so does its density  Saltier water tends to sink to the bottom, while less salty water will rise  In areas where rivers meet the ocean, there is often a layer of fresh water “floating” on denser, salty water near the bottom ☺

54  Near the polar regions, the ice caps are formed from frozen sea water  However, the salt does NOT freeze! It stays in the water ☺

55  As the ice forms, the salinity of the remaining water increases. This denser water then sinks towards the bottom, forcing the water at the bottom to move towards the surface in a process called upwelling. ☺

56  These upwellings bring nutrients up from the bottom, and carry oxygen to the bottom  Because of these upwellings, these areas are full of life despite being very cold ☺

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58 Density Summary Density will INCREASE if: 1. Temperature decreases OR 2. Salinity increases Density will DECREASE if: 1. Temperature increases OR 2. Salinity decreases ☺

59 Ocean History and Features  All water on earth appeared due to volcanic activity  Water vapor expelled by volcanoes condensed and fell as precipitation, collecting in the ocean basins ☺ ☺

60  Life first appeared in the oceans. The water helped protect this earl life from the sun’s damaging ultraviolet radiation  These early photosynthetic bacteria slowly added oxygen to the atmosphere, producing the ozone layer which allowed life to develop on land ☺

61  Light levels, temperature, salinity, and pH in the oceans vary greatly  Light only penetrates about 1,000 feet in the clearest ocean waters; most water below 300 feet is always dark ☺

62  Aphotic zone – area of the ocean with no light; majority of the ocean  All photosynthetic organisms must remain in the photic (lighted) zone ☺

63  Temperatures range from -2°C in the deepest ocean and polar regions to 40°C in shallow tropical lagoons  Water near the surface is generally the warmest ☺

64  Thermocline – depth at which water temperature changes rapidly  The thermocline forms a barrier in the water column. Below it, there is generally little oxygen ☺

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66  Pycnocline – depth at which the salinity of water changes rapidly; acts very similar to thermocline in preventing the mixing of water  Often found at similar depth as the thermocline ☺

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68  pH – measure of how acid or basic (alkaline) a substance is  pH is measured on a scale of 0 – 14  7 is neutral (pure water)  Below 7 is acid, above 7 is basic (alkaline) ☺

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70  Normal ocean pH ranges from 6 – 8.5, depending on the area ☺