Properties of H 2 O Biology

Neutral in charge and polar covalent.  Covalent bonds between hydrogen and oxygen atoms result in uneven sharing of electrons.  Hydrogen Bonds between water molecules. See diagrams.

PolarNonpolar Water soluble Asymmetrical: uneven electron distribution, do not share electrons Examples: water, sugar, salt, ethanol, hydrogen sulfide The electrons of the polar covalent bonds spend more time near the oxygen than the hydrogen. Polarity allows water to form hydrogen bonds with each other. Ionic compounds dissolve in water to form ions: for most biological reactions to occur the reactants MUST dissolve in water. Fat soluble Symmetrical: electrons are evenly distributed. Strongly covalently bonded Examples: fats, oils, cell membranes and cell walls, carbon dioxide, gasoline.

Water is polar: regions have a slight positive (H+) and slight negative charge (O-) Oxygen atoms are slightly negative and hydrogen is slightly positive= hydrogen bond. Can form between any hydrogen atom that is covalently bonded to an atom that has a strong attraction for electrons. Each H 2 O molecule can form 4 hydrogen bonds with 4 other water molecules. Groups of hydrogen bonds are very strong.

Place below the hydrogen bonding notes We also find them in our DNA and proteins! Covalent Bond

Dissolves almost all substances (mostly polar) Provides a medium in which other molecules can interact. Solution: uniform mixture of two or more substances. Solvent: substance present in the greatest amount. Solute: substance present in lesser amounts. Examples: water= solvent, koolaid powder / sugar= solute, Koolaid= solution Hydrophobic: “water fearing” molecules, nonpolar molecules separate in water. Example= fats Hydrophilic= “water loving” molecules, polar molecules dissolve in water. Examples= DNA, sugars, proteins Amphipathic= molecules have both polar and nonpolar regions. Example= phospholipids

Cohesion & Surface Tension Water molecules stick together Why? Hydrogen bonding Causes: surface tension, which means how difficult it is to break the surface. Makes a skin on the surface of the water. Examples: – Skipping rocks, rain drops beading up on a car, water droplets on a penny, spider walking on water

Water molecules stick to other objects Examples: – Meniscus in a graduated cylinder – Wet microscope slides sticking together

Movement of liquid through a narrow passage / H 2 O molecules stick to tubes of small diameter. Result of cohesion of water molecules sticking to each other and adhesion of water molecules to another surface. Examples: – Drinking straw – Food coloring added to water to dye flowers – Plants transport water from roots to leaves (against gravity)

Water resists changes in temperature; therefore water must absorb more heat energy to increase temperature. Very important because our cells release a lot of heat, and water absorbs that heat, which allows us to regulate cell temperatures= HOMEOSTASIS Hydrogen bonds must break in order to raise 1 g. of water by 1 C. Examples: oceans cool slower than land due to the high heat capacity of water.

Vaporization = evaporation & boiling Water is changing from a liquid to a gas Liquid molecules enter the air Evaporation produces a cooling effect Hydrogen bonds must be broken before water can evaporate and this requires a lot of energy. Example: sweating (humans) or panting in dogs= dogs can’t sweat through their skin, they pant to circulate air through their bodies to cool down= evaporative cooling.

Water freezes = crystalline structure maintained by hydrogen bonding O C = Freezing Ice is less dense than liquid water because the hydrogen bonds are positioned in a way that pushes the molecules apart= lowers density. Advantages: protects aquatic ecosystems If ice filled the entire lake or ocean, from bottom to top, it would sink, fill the entire area, and kill all aquatic life. Also allows turnover of nutrients – In the spring, the ice melts, water sinks, and pushes up the nutrient rich water.

Exists in all three states

Guess the property?????

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pH: Acids and Bases Biology

1. Covalently bonded water molecules ionize -the atoms dissociate (break apart) into ions. 2. When water ionizes, it releases a small but equal number of H+ (hydrogen) and OH- (hydroxide) ions -because of equal numbers of + and – ions, its pH is neutral. What makes an acid?

3. When acid molecules dissociate in water, they release hydrogen ions (H+). 5. Bases are molecules that take up hydrogen ions or release hydroxide (-OH - ) ions. The pH scale is a logarithmic scale; an acid with a pH of 6 has 10 times more hydrogen ions than a pH of 7, and 100 times more H + ions than a base with a pH of 8.

Acid Substance that releases hydrogen ions (H + ) in a solution Properties: – pH 0 – 6.9 – Stings skin – Tastes sour – Corrosive Common Acids: – HCl- hydrochloric acid – Citric acid – Sulfuric acid – Battery acid – Urine – Lemon juice Base Substance that releases hydroxide (OH-) ions in a solution. Properties: – pH – Strong bases can burn skin – Tastes bitter – Slippery Common Bases: – Oven cleaner – Toothpaste – Human Blood – Pepto Bismol – Windex – Baking Soda

pH scale measures degrees of acidity and alkalinity 1-14 Scale Measures hydrogen ion concentration (H+) Neutral is 7, example water The pH Scale

How do we test pH? pH Paper: Turns a color when placed in a substance. Phenolphthalein: when a drop is placed in the substance, the color of the substance will change. Bases turn purple. Acids remain the same. Litmus Test: Base turns blue / Acid turns red

pH paper Litmus Paper How do we test pH?

pH and our environment If pH is too high or low in our drinking water, it can alter homeostatic levels. It can potentially kill wildlife. Acidic water can corrode your pipes, leaving contaminants in the water. Alter the function of enzymes. Controls cell processes such as metabolism. The closer the pH is to , the higher your level of health and ability to resist diseases. Ocean acidification. There has been evidence of ocean acidification during each mass extinction. – CO 2 + H 2 O  H 2 CO 3  HCO H +

ACID WATER!!! Acid Lakewater can kill fish Acid Rain can kill trees 6ma2an4rctge7ji53ievra0

How is pH regulated in our bodies? Through buffers-> compounds that can bind to H+ ion when the H+ concentration increases and can release an H+ ion when the H+ ion decreases. Buffer “locks up or stops” the H+ ions in order for our bodies to maintain homeostasis. Example-> normal pH of blood is (slightly basic), therefore a small change could disrupt cells and potentially be fatal.

A change of one pH unit changes the hydrogen ion concentration by a factor of 10. Example: A solution with a pH of 1 has 10 times more hydrogen ion concentration than a pH of 2; 100 x’s more hydrogen ion concentration than a pH of 3, etc. pH of 1 has one million times more hydrogen ion concentration than a pH of 7. To simplify, scientists converted the exponents -7, 0, and -14 to 7, 0, and 14

Draw the pH Scale