MODERN BIOLOGY Ch. 2.3 Water, Solution, pH
Polarity: “Electron hogs and electron weaklings” • In covalent bonds where the “sharing” is unequal (like in water). • This creates a shift in the electron cloud around the stronger atom making it partially negative (-). • The shift also partially exposes the proton of the hydrogen making the hydrogen areas partially positive (+). • This makes water a polar (think of the + and – poles on a magnet) covalent (shared valence electrons) molecule.
Solubility of Water: • The polar nature of water allows it to dissolve polar substances (sugars), ionic compounds (salts), and some proteins. • Water does not dissolve nonpolar molecules (no poles / equal sharing: like O2). • “Like dissolves like.”
Hydrogen Bonding ( opposites attract too.) • The force of attraction between the + area of one molecule and the - area of neighboring molecules. • Hydrogen Bonding accounts for the unique properties of water. • cohesion: water sticks to itself (a glass of water fuller than full.) • adhesion: water sticks to other things (meniscus) • temperature moderation or the ability to absorb and release large amounts of heat with only slight changes in its own temperature: • moderation between day / night • summer / winter • coastal vs. inland climates • global moderation • evaporative cooling • density of ice
Solutions • Solute into solvent makes a solution. • Salt in water makes a salt solution. • Alcohol in water makes a solution. • (Solvent: whichever is in greater quantity) • Concentration: the amount of solute in a volume of solvent. • 2g salt diluted up to 100 ml with water = 2% salt solution • saturated solution: no more solute can dissolve. • Aqueous solutions: water is the solvent
Acids and Bases • Ionization of Water: H2O H+ + OH- (hydrogen ion and hydroxide ion) water is neutral in pH. • ORH+ + H2O H3O+ (hydronium ion) • Acid: substances that put H+ into solution • Base: substances that put OH- into solution. • pH: range is 0 to 14. • Near zero is very acidic • Near 14 is very alkaline or basic. • 7 is neutral (an equal # of H+and H3O+ ) • Buffers: neutralize small amounts of acid or base