Water Chapter 3

Water Life began in water 2/3s of an organisms body Organisms grow or reproduce in a water-rich environment.

Water Molecule Covalent bonding Oxygen is more electronegative Polar molecule Polarity of water underlies its chemistry Chemistry of life.

Polar molecule

Hydrogen bonding

Fig. 3-2 Hydrogen bond – H + H O – – –

Properties of water Cohesion: Attraction between water molecules Responsible for surface tension of water

Properties of water Adhesion: Attraction of water between other molecules Capillary action

Properties of water Moderation of water temperature Water is a liquid at moderate temperatures Specific heat: Amount of heat needed to a raise 1 gram of a substance 1 0 Celsius Waters specific heat is 1 calorie/gram/ 0 C (4.18Joules)

Properties of water Evaporative cooling Heat of vaporization: Amount of heat needed to change 1 gram of a substance from a liquid to a gas. 586 Calories (2260 Joules)

Properties of water Ice floats Less dense

Fig. 3-6a Hydrogen bond Liquid water Hydrogen bonds break and re-form Ice Hydrogen bonds are stable

Properties of water Solvent Water surrounds ionic & polar molecules Table salt or sugar Aqueous solution Molarity

Fig. 3-7 Cl – Na Cl – – – – – – – – – Na + – – – +

Hydrophobic fear of water Common in non-polar molecules Non-polar molecules tend to aggregate in water Hydrophobic exclusion

Hydrophilic water-loving Common in polar molecules

Fig. 3-UN2 Hydronium ion (H 3 O + ) Hydroxide ion (OH – ) 2H 2 O H H H H H H H H O O O O Ionization Process of spontaneous ion formation H 2 OH + + OH - Dissociation

pH Measurement of the concentration of hydrogen ion. pH = -log[H + ] Acid: Increase concentration of H + ions or a lower pH. Base: Decrease in concentration of H + ions or a higher pH.

Fig. 3-UN5 Bases donate OH – or accept H + in aqueous solutions Acids donate H + in aqueous solutions Acidic [H + ] > [OH – ] Neutral [H + ] = [OH – ] Basic [H + ] < [OH – ]

pH

Fig. 3-9 Neutral solution Acidic solution Basic solution OH – H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Neutral [H + ] = [OH – ] Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ] pH Scale Battery acid Gastric juice, lemon juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Saliva Pure water Human blood, tears Seawater 9 10 Milk of magnesia Household ammonia Household bleach Oven cleaner

Buffer Substance helps maintain a balanced pH Accepts H + ions when excess Donates when there are too few.

Buffer Blood pH is approximately 7.4. Bicarbonate ion helps maintain the pH of the blood. Blood acidosis: pH drops 0.2 to 0.4 points on the pH scale Blood alkalosis: pH goes up 0.2 to 0.4 points on the pH scale

Buffer Bicarbonate ion H 2 CO 3 HCO H +

Acid rain Sulfuric acid Nitric acid

Acid rain