Chapter 2 The Chemistry of Life The Water - polarity H 2 O is a polar A water is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. Water Sec. 2-2 Properties of Water The Water Molecule - Polarity 2 H atoms and 1 O atom are covalently bonded O end has partial negative charge (-) H end has partial positive charge (+) Water The Water Molecule - Polarity The larger nucleus of the oxygen atom with its 8 protons (8 positive charges) has a greater attraction for hydrogen s electrons than does hydrogen s one proton nucleus (1 positive charge). Water t Weak Bonds between H 2 O s The partial negative charge (-) of the O end of one H 2 O and the partial positive charge (+) of the H end of another H 2 O are attracted to one another (like magnets). Hydrogen 1
- Partial Positive end of H 2 0 + - + Partial Negative end of H 2 0 + - + Hydrogen Hydrogen Bonds between H 2 O s These between attractions are known as hydrogen. Hydrogen Hydrogen Bonds between H 2 O s Bonding - Cohesion (between H2O s) are not as strong as covalent or ionic. Hydrogen is an attraction between s of the same substance (co- means common). Because of its hydrogen bonding, H 2 O is extremely cohesive. Cohesion Bonding - Cohesion One result of the cohesion of H 2 O s is surface tension The tight film that t forms on the surface of water that allows some spiders and insects to walk on a pond s surface. Cohesion Bonding - Adhesion is an attraction between s of different substances. (ad- means toward) Adhesion 2
Adhesion Bonding - Adhesion Capillary action, the tendency of H 2 O to be drawn up narrow tubes, results from the strong adhesive force of H 2 O. Adhesion Capillary Action Another Result of Hydrogen Bonding is that Before s of water gain or lose thermal energy (i.e. the goes up or down) H- must be broken or formed. This makes water resistant to increases or decreases. Resistance to Which will make larger droplets, hot or cold water? Which will stick to your windshield longer, hot or cold water? Are you pondering what I m pondering? Water in Amixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. Water in 3
Water in forms two types of mixtures: Solutions Suspensions Water in Water in A solution is a mixture in which all of the components are evenly distributed throughout. A solute (sol yoot) is the substance that is dissolved in a solution. (ex. table salt in a saltwater solution) A solvent is the substance in which the solute dissolves. (ex. the water in which salt dissolves to make a saltwater solution). Water in Solution Water in Cl - Cl - Na + Adhesion Water Water Water in Fig. 2-9, pg. 42 forms two types of mixtures: Solutions Suspensions Water in Water in (suspension) Acids, Bases, Flour in water Asuspension is a mixture of water and nondissolved material. Water in Acidity and Alkalinity (better than having to say basicity ) are determined by the relative number of H + (hydrogen) ions compared to the number of OH - (hydroxide) ions in a solution. Acids have more H + than OH - Bases have more OH - than H + Acids, bases, 4
Acids, Bases, Chemists devised a scale to measure acidity called the ph scale. The ph scale ranges between 0 and 14 with values below 7 indicating acids and values above 7 indicating bases. At ph 7, a solution is neutral (neither acid nor base). This is the point at which a solution has the same number of H + and OH - ions. Acids, bases, ph scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 acid neutral base Acids, Bases, Acids, Bases, Pure H 2 O has a ph of 7 because when H 2 O dissociates (which is quite rarely) H + - 2 O H + OH Water hydrogen ion + hydroxide ion Equal numbers of H + and OH - are formed Acids, bases, Inc reasingly Basic Neutral Increasingly Acidic Oven cleaner Bleach Ammonia solution Soap Sea water Human blood Pure water Milk Normal rainfall Acid rain Tomato juice Lemon juice Stomach acid Acids, Bases, Acids, Bases, When strong acids are placed in H 2 O, they dissociate almost completely. HCl H + + Cl - The concentration of H + increases greatly and there are now many more H + ions than OH - ions. Acids, bases, ph is below 7 Acids have a sharp or sour taste. ex. Lemons, vinegar, tomatoes, coffee Acids, bases, 5
Acids, Bases, When strong bases are placed in H 2 O, they also dissociate almost completely. NaOH Na + + OH - The concentration of OH - increases greatly and there are now many more OH - ions than H + ions. Acids, bases, ph is above 7. Bases have a bitter taste and feel slippery when in water. Ex. ammonia Acids, Bases, Al Kaline (get it?) Resistance to Acids, bases, and ph Acids, Bases, - Recap Acidic solutions contain higher concentrations of H + ions than pure water and have ph values below 7. Basic, or alkaline, solutions contain lower concentrations of H + ions than pure water and have ph values above 7. Acids, bases, Buffers The chemical reactions that keep living things alive only operate within a narrow ph range This involves the process of HOMEOSTASIS. keep the ph within this range. Buffers Buffers A buffer is a weak acid or base that reacts with strong acids or bases to prevent sharp, sudden s in ph. do this by taking up excess H + and OH - ions. Example buffered aspirin (Bufferine) Buffers Uneven distribution of electrons Recap The Properties of Water cohesion water polar H-bonding H 2 O adhesion Attraction between H 2 O s Capillary action Recap 6
- + + End of 2-2 7