Chapter 3 WATER AND THE FITNESS OF THE ENVIRONMENT Themes: Emergent Properties Structure and Function Science, Technology and Society
Objectives: • Polarity of water molecules • Cohesion of water • Water moderates temperature on Earth • Ice floats… why? • Solvent of life • Organisms are sensitive to pH changes • Acid Rain
Root Words: • Kilo – • Hydro – • - philos • - phobos
Hydrogen Bonding is the Most Important Concept: Most of water’s characteristics are due to the principle of hydrogen bonding. • - • + • + • + • +
Formation of hydrogen bonds -Releases heat • Breaking of hydrogen bonds - Absorbs heat Cohesion - hydrogen bonds holding water molecules together, helps water move up a tree. • Surface tension - cohesion • Beading of water – cohesion • Water’s high heat of evaporation is due to hydrogen bonding. • Heat of Vaporization - quantity of heat a liquid must absorb for 1 gm of water to be converted from liquid to a gas.
Specific heat - amt. of heat that must be absorbed or lost by 1gm. Of a substance to change it’s temp. 1° C. Water is 1cal/g/1°C. • Water has high specific heat compared to other substances , thus it resists changes in temp. when it absorbs or releases heat. • Water also has high boiling point.
ICE - Water expands when it freezes. Ice is less dense than liquid water. WHY??? • NOTE - hydrogen bonding causing less H20/vol
A CRYSTAL OF TABLE SALT DISSOLVING IN WATER. • The H+ regions of the polar water molecules are attracted to the chloride anions (green), the O- regions cling to the sodium cations (yellow). The sphere of water molecules surrounding a solute ion (or molecule) is called a hydration shell.
HYDROPHILIC - “WATER LOVING” SUBSTANCES THAT HAVE AN AFFINITY FOR WATER EVEN IF THEY DO NOT DISSOLVE IN WATER. (IONIC OR POLAR MOLECULES). • HYDROPHOBIC - “WATER FEARING” WILL NOT DISSOLVE IN WATER OR HAVE NO AFFINITY FOR WATER. (NON-IONIC, NONPOLAR SUBSTANCES)
CALORIES & KILOCALORIES: Calories = amt. of heat needed to raise 1 gm. of water 1 ° C. Kilocalorie = 1000 calories. If 10 ml of water was raised 1 ° C this would be 10 calories.
MAKING AQUEOUS SOLUTIONS: To make a solution - dissolve solute in small amt. of water THEN add water to get the final volume. A mole is = in number to mol. weight of a substance in grams. Molecular weight = sum of weights of all atoms in a molecule. EXAMPLE - C2H5O2NH2 mol. Wt. : H =7; O = 32; N= 14; C = 24 (77)
MOLARITY - # of moles of solute per liter of solution. • 77 g of solute in 1 liter of water = 1 M solution. • 7.7 g of solute in 1 liter of water = 0.1 M solution. • REMEMBER - you are attempting to keep the same proportion of solute to solvent in the solution.
ACIDS, BASES & BUFFERS: • ACIDS: H+ (proton) donors in aqueous solution (increase H+ ions in solution.) • BASE : H+ (proton) acceptor in aqueous solution (reduces in H+ ions in solution.). Also reduce H+ ions indirectly by dissociating to form OH- ions (combine with H+ to form H2O). • Aqueous -of, like, or containing water; watery
pH Scale: -log [H] & is a ten fold difference between whole #’s. EXAMPLE: pH 6 to pH 5 = 10 times increase in acidity. • EXAMPLE:pH 6 to 4 = 100 times increase in acidity. • 0 1 2 3 4 5 6 • (Strong acid) (med. acid) (weak acid)
pH Scale - [H+] [OH-] = 10 -14 pH 7 [H+]-7 [OH]-7 = 10-14 pH 6 [H+]-6 [OH]-8 = 10-14 • Common acids - lemon juice, vinegar, coffee. • Common bases - seawater(pH8) ammonia, bleach.
DO ALL SUBSTANCES HAVE MEASURABLE pH? • NO !!!!! Why??? • Substance must dissolve in water (dissociate in water). • EXAMPLES: Hydrocarbons which are nonpolar - gasoline, kerosene, butane, methane.
BUFFERS: Chemicals that minimize changes in pH by: • Accepting H+ OR release H+ ions • (acid solution) ( basic solution) • NOTE: Bases are also called alkaline.
WATER-SOLUBLE PROTEIN • Even a molecule as large as a protein can dissolve in water if it has enough ionic and polar regions on its surface. The mass of purple here represents a single such molecule,which water molecules are surrounding.