Chapter 3 WATER AND THE FITNESS OF THE ENVIRONMENT

Themes:

1. Emergent Properties

2. Structure and Function

3. 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 -Formation of hydrogen bonds - Releases heatReleases heat

•Breaking of hydrogen bonds - Breaking of hydrogen bonds - Absorbs Absorbs heatheat

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 Water’s high heat of evaporation is due to hydrogen bonding.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: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 ScalepH Scale - [H - [H++] [OH] [OH--] = 10 ] = 10 --

1414

•pH 7 [HpH 7 [H++]]-7-7 [OH] [OH]-7 -7 = 10 = 10-14-14

•pH 6 [HpH 6 [H++]]-6-6 [OH] [OH]-8 -8 = 10= 10-14-14

•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.

•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.

•WATER-WATER-SOLUBLE SOLUBLE PROTEINPROTEIN