Properties of Water and pH

water molecules

(life depends on water)

individual water molecules are created through polar covalent bonds

water molecules are polar and because of this, multiple water molecules are bonded by H bonds

water attracts/is attracted to other polar molecules and ions

hydrophilic

polar molecule that readily interact with or dissolves in water (water loving)

hydrophobic

nonpolar molecule that doesn’t interact well with water (water hating - phobic = phobia of water)

heat

measure of the total kinetic energy due to molecular motion

(more movement = more kinetic energy = more heat)

liquid

water molecules constantly forming and breaking H bonds as water molecules move past each other which creates kinetic energy and causes bonds to break.

gas

when water heats up enough, the water molecules escape into the air as a gas

solid

as water cools, there is not enough kinetic energy to break H bonds.
so, water molecules freeze, expand, and form a crystalline structure (solid) maintained by H bonds
solid is less dense than liquid (unique to water - icebergs)

4 properties of water

1. high heat capacity

2. high heat of vaporization

3. solvent

4. cohesion and adhesion

specific heat

amount of heat one gram of a substance must absorb or lose to change it’s temperature by 1 degree C

high heat of vaporization

amount of energy required to change one gram of liquid substance to a gas

evaporation

conversion of liquid to gas

evaporative cooling

energy is taken up during evaporation, cooling the surrounding environment

solvent

substance capable of dissolving other polar molecules and ionic compoundssolut

solute

any component dissolved in a solvent

sphere of hydration

a ring of water molecules formed by charges associated with a solution

solution

homogenous mixture of one or more solutes dissolved in a solvent

dissociation

occurs when atoms or groups of atoms break off from molecules and form ions

surface tension

capacity of a substance to withstand rupturing when placed under tension or stress

cohesion

water molecules are more attracted to each other than the surrounding air/surface (think of a seemingly overflowing cup of water) (responsible for shape of water droplets)

adhesion

attraction between water molecules and other molecules (sometimes stronger than cohesion especially when exposed to charge surfaces)

capillary action

water molecules are more attracted to charged glass tube than other water molecules and “climb” up the tube

pH

indicates acidity or basicity of a solution

it measures the concentration of hydrogen ions in a solution

chemical equillibrium

when water molecules randomly dissociate into equal numbers of H ions and OH- ions, which happens in both directions at the same rate

acid

substances that increase the H+ concentration of a solution.

strong acids release more H+ than weak acids when dissociating.

low concentration of H+ = high acidity = low pH

base

substances that reduce the H+ concentration of a solution.

some release OH- while others bind H+

low concentration of H+ = low acidity = high pH

pH scale

ranges from 0-14

• >8 - basic

• =7 - neutral

• <7 - acidic

buffer

substances that minimize changes in concentration of H+ and OH- in solutions

readily absorb H+ and OH- ions to keep solution near neutral

example of buffer

bicarbonate bonds with H+ to form carbonic acid which removes H+ and stops blood from becoming acidic. if there is a buildup of carbonic acid it’s converted to CO2 gas and H2O which stops blood from becoming too basic.