Chapter 3 Water and the Fitness of the Environment

1.Why is water so important? –Living cells are 70-95% water –Water covers ¾ of the Earth –Life evolved in water –Water exists in all 3 states in nature Ch 3: Water and the Fitness of the Environment

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? Ch 3: Water and the Fitness of the Environment

Figure 3.2 Hydrogen bonds between water molecules Hydrogen bonds  + + ++ H H ++ ++ –– –– –– ––

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are 4 properties of water based on hydrogen bonding? –Cohesion – hydrogen bonds holding a substance together –Adhesion – hydrogen bonds hold a substance to another polar substance Ch 3: Water and the Fitness of the Environment

Figure 3.3 Water transport in plants. Water can defy gravity

Figure 3.4 Walking on water – surface tension

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? –Cohesion – hydrogen bonds holding a substance together –Adhesion – hydrogen bonds hold a substance to another polar substance –Moderation of temperature – high specific heat Water resists temperature changes when it absorbs or releases heat Temp. on Earth is stable (3/4 covered by water) Coast is milder than inland Marine environments are stable –Evaporative cooling – hottest molecules leave, cooling the surface –Solid water floats Ch 3: Water and the Fitness of the Environment

Figure 3.5 Ice: crystalline structure and floating barrier Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? –Cohesion – hydrogen bonds holding a substance together –Adhesion – hydrogen bonds hold a substance to another polar substance –Moderation of temperature – high specific heat –Evaporative cooling – hottest molecules leave cooling the surface –Solid water floats –Universal solvent - dissolves polar & ionic substances Ch 3: Water and the Fitness of the Environment

Figure 3.6 A crystal of table salt dissolving in water Negative Oxygen regions of polar water molecules are attracted to sodium cations (Na + ) Cl – – – – – Na + Positive hydrogen regions of water molecules cling to chloride anions (Cl – ) – – – – – – Na + Cl –

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? 5.What’s the difference b/w hydrophilic & hydrophobic? –Hydrophilic – “water loving” – polar –Hydrophobic – “water fearing” – non-polar Ch 3: Water and the Fitness of the Environment

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? 5.What’s the difference b/w hydrophilic & hydrophobic? 6.What is molarity? - Moles of solute per liter of solution Ch 3: Water and the Fitness of the Environment

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? 5.What’s the difference b/w hydrophilic & hydrophobic? 6.What is molarity? 7.What is meant by the “dissociation of water?” Ch 3: Water and the Fitness of the Environment

Reaction producing hydroxide and hydronium ions H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + At equilibrium, in pure water at 25°C # of H + ions = # of OH - ions [H + ] = [OH - ] = 1/10,000,000 M = M

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? 5.What’s the difference b/w hydrophilic & hydrophobic? 6.What is molarity? 7.What is meant by the “dissociation of water?” 8.What is the difference b/w an acid& a base? –Acid – substance that increases the [H + ] of a sol’n – pH < 7 –Base – substance that reduces the [H + ] of a sol’n – pH > 7 Ch 3: Water and the Fitness of the Environment

Figure 3.8 The pH scale and pH values of some aqueous solutions Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ] Neutral [H + ] = [OH – ] Oven cleaner pH Scale Battery acid Digestive (stomach) juice, lemon juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Pure water Human blood Seawater Milk of magnesia Household ammonia Household bleach

pH scale -log [H + ] In any aqueous sol’n: [H + ] x [OH - ] = Neutral sol’n: [H + ] = & [OH - ] = Acidic sol’n: [H + ] = then [OH - ] = Basic sol’n: [H + ] = then [OH - ] = What is the difference in [H + ] between sol’ns of pH2 & pH6? pH2 has 10,000 more H + than pH6 Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ] Neutral [H + ] = [OH – ] pH Scale

1.Why is water so important? 2.What kinds of bonds are within a water molecule? 3.What kinds of bonds hold water molecules together? 4.What are some properties of water based on hydrogen bonding? 5.What’s the difference b/w hydrophilic & hydrophobic? 6.What is molarity? 7.What is meant by the “dissociation of water?” 8.What is the difference b/w an acid& a base? 9.What are buffers? –Substances that minimize sudden changes in pH –Can both accept & donate H + Ch 3: Water and the Fitness of the Environment

Figure 3.9 Acid precipitation and its effects on a forest More acidic Acid rain Normal rain More basic