2-3: WATER + SOLUTIONS

The chemical reactions of all living things take place in an aqueous environment (i.e. WATER)

Let’s look at some of the unique properties of water….

POLARITY

RECALL - - H + O combine by covalent bond to make 1 water molecule = H2O These atoms do not share electrons

evenly Oxygen has moremore positive charges

(8 p+) than Hydrogen (1 p+), thus pulling the electrons more towards its nucleus

POLARITY (cont.)

This results in a slight, uneven electrical charge in the molecule

Shape of water = bent (angle created)

Even though water is neutral, regions have slight charges Oxygen – slightly negative Hydrogen – slightly positive

Still more Polarity… Because of these slight charged regions,

water is POLAR Is known as the “Universal

Solvent” because of this propertyIonic compounds dissolve into

dissociated ions, that are essential to normal body operations

Example: SALT

HYDROGEN BONDING

Hydrogen bonds hold water molecules together Positive region attracted to

negative region of molecules Very weak bond – easily

broken

Keep adding water molecules together…

And eventually, you get this…

Cohesion + Adhesion Cohesion – an attractive force between

like particles of the same kind Example? Surface tension

Adhesion – an attractive force between unlike substances

Example? If cohesion + adhesion work together, water

molecules can move upwards against gravity known as CAPILLARITY

Examples of Capillarity

TEMPERATURE MODERATION

In order to change its temperature, water must gain or lose large amounts of energy Must break/reinforce H-bonds to

increase/decrease temp. Cells can maintain temp. even if outside

temp. changes

Let’s watch a video…

Properties of Water

SOLUTIONS

Solution – mixture in which one or more substances are uniformly distributed in another substance

Parts of a solution: Solute – substance dissolved in solution Solvent – substance that does the

dissolving Ex. Sugar in Water

SOLUTIONS (cont.)

Concentration – measurement of the amount of solute dissolved in a fixed amount of solution Ex. 2g/100mL = 2% solution

The more solute dissolved, the higher the concentration Saturated – no more solute can be

dissolved

SOLUTIONS (cont.)

Aqueous – water is the solvent Universal Solvent

Marine microorganisms live in it Plants get nutrients from it Our cells are filled with it

ACIDS + BASES

Dissociation of water – breaking apart of water molecules into two opposite charges H2O H+ + OH-

OH- = Hydroxide ion Free H+ ion can react w/ other water

molecules H+ + H2O H3O+

H3O+ = Hydronium ion

ACIDS + BASES (cont.)

Acid Hydronium ions > Hydroxide ions Characteristics of Acids:

Low pH number (0-6) Sour taste Can be highly corrosive to metal

ACIDS + BASES (cont.)

Base (Alkaline) Hydroxide ions > Hydronium ions Characteristics of a base:

High pH number (8-14) Bitter taste Tend to feel slippery

pH pHpH – stands for power of Hydrogen

pH scale – measures concentration of solutions – can use litmus or pH paper Ranges from 0-14 a logarithmic scale

Change in 1 pH unit = tenfold change in acidity or alkalinity Ex. pH=3 vs. pH=4 pH of 3 has 10 times more H3O+ ions than

pH of 4 10x (x = pH # difference)

pH = 7

Neutral Hydronium ions = Hydroxide ions

Example: Pure Water

BUFFERS

Buffer – chemical substances that neutralize small amounts of acids or bases To neutralize an acid, add a base To neutralize a base, add an acid

Buffers used to maintain homeostasis in your body

Example – an upset stomach