Chapter 3: Water

Water: The Molecule That Supports All of Life Water is the biological medium here on Earth All living organisms require water more than any other substance ¾ of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable

Properties of Water The polarity of water molecules Allows them to form hydrogen bonds with each other Contributes to the various properties water exhibits that make life as we know it possible Hydrogen bonds ++  H H ++ ++  – –  – –  –  – –

Properties of Water Cohesion Is the bonding of like polar molecules to neighboring like polar molecules Is due to hydrogen bonding

Properties of Water Adhesion Is the bonding of polar molecules to unlike neighboring polar molecules It is also due to hydrogen bonding

Cohesion and Adhesion Capillary action

Cohesion and Adhesion

Heat and Temperature Kinetic Energy Is the energy of motion Heat is the measure of the total amount of kinetic energy due to molecular motion Temperature measures the intensity of heat

Specific Heat Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC Water has a high specific heat, due to hydrogen bonding, which allows it to minimize temperature fluctuations Heat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds form

Specific Heat Simply put: If you add heat to water, it will be get warmer slower compared to a liquid without hydrogen bonds If you take away heat from water, it will cool slower compared to other liquids

San Diego 72° 40 miles Pacific Ocean 70s (°F ) 80s 90s 100s Santa Barbara 73° Los Angeles (Airport) 75° Burbank 90° San Bernardino 100° Riverside 96° Santa Ana 84° Palm Springs 106° Specific Heat

Evaporative Cooling Evaporation Is the transformation of a substance from a liquid to a gas For water, H bonds BETWEEN water molecules must be broken for evaporation to occur Evaporative cooling Is due to the molecules with the most kinetic energy entering the gas state, leaving behind those with less energy This phenomenon can cool biological organisms Evaporation is impeded by high humidity however Expression: It’s not the heat but the humidity!

Ice Solid water, or ice Is less dense than liquid water Floats in liquid water Since ice floats in water Life can exist under the frozen surfaces of lakes and polar seas

Ice The hydrogen bonds in ice are more “ordered” than in liquid water, making ice less dense In same space, fewer water molecules can fit when frozen compared to liquid water Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond

Water: Solvent of Life Water is a versatile solvent due to its polarity It can form aqueous solutions

Water as a Solvent The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them Cl – – – – – Na – – – – – – Cl –

Water as a Solvent A solution is a liquid homogenous mixture of 2 or more substances The solute is the substance that is dissolved in a solution The solvent is the dissolving agent of a solution, often water (aqueous)

Water as a Solvent A hydrophilic substance Does have an affinity for water Typically contains polar covalent or ionic bonds A hydrophobic substance Does not have an affinity for water Typically contains non-polar covalent bonds (like fats/oil) Expression: Oil and water (don’t mix); Meaning incompatible things or people (can’t be made to work well together)

pH Water can break apart into hydrogen ions (H + ) and hydroxide ions (OH - ) Changes in the concentration of these ions can have a great affect on living organisms

pH The pH of a solution Is determined by the concentration of hydrogen ions, [H + ] [H + ] high in an acid [H + ] low in a base pH = -log[H + ] e.g. A solution with [H + ] = 1 x M would have a pH value of 5

Acids and Bases An acid Is any substance that increases the H + concentration of a solution A base Is any substance that reduces the H + concentration of a solution

pH Scale pH scale is from 0-14 Solutions with pH values < 7 are acids pH values = 7 are neutral pH values > 7 are bases 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 For example, a testing kit indicates a pH level of 3 in a solution. This means: The solution is an acid The [H + ] = 1 x M or 0.001M Another solution measures pH 9. This means: The solution is a base The [H + ] = 1 x M or M pH3 has more H + than pH 9 (0.001M > M)

Pretend iClicker ? The concentration of H + ions in a solution is 1 x M. This tells you the pH of the solution is A.pH 8, and it is an acid. B.pH 8, and it is a base. C.pH 6, and it is an acid. D.pH 6, and it is a base E.pH 14, and it is an acid.