We are here on earth to do good for others.What the others are here for, I don't know.

W. H. Auden

WATER UNDERGOES A SLIGHT DISSOCIATION.

THE REACTION IS:

H2O = H+ + OH-

IN PURE (NEUTRAL) WATER, THE CONCENTRATIONS OF HYDROGEN ION, H+, AND HYDROXIDE ION, OH-, WILL BE EQUAL.

THESE CONCENTRATIONS ARE SMALL – ONLY 1 X 10-7 M.

WHEN WE TALK ABOUT WATER BEING ACIDIC OR BASIC, WE DESCRIBE THE SITUATION IN TERMS OF pH.

pH = - log (H+)

THE pH IS THE NEGATIVE LOG OF THE HYDROGEN ION CONCENTRATION.

IN PURE WATER,

pH = - log (10-7) = 7

SO, NEUTRAL WATER HAS A pH of 7.

ION - atom or group of atoms carrying a charge

ACID - produces hydrogen ion, H+ , on solution, has pH less than 7

BASE - produces hydroxide ion, OH-, on solution, has pH greater than 7

NEUTRAL - produces same number of hydrogen and hydroxide ions, has pH of 7

INDICATOR - a dye that gives a particular color with a given pH

pH paper - paper that gives a particular color with a given pH

WHY ARE WE STUDYING pH?

WHY ARE WE STUDYING pH?

BECAUSE pH CAN HAVE A MAJOR IMPACT ON THE ENVIRONMENT.

pH OF LAKES, STREAMS AND GROUNDWATER CAN CHANGE DEPENDING ON WHAT WE PUT IN THE AIR OR POUR ON THE GROUND.

ACID RAIN IS CAUSED BY BURNING FOSSIL FUELS AND AUTOMOTIVE EXHAUST.

BURNING FOSSIL FUELS PRODUCES SULFUR DIOXIDE (SO2) AND NITROGEN DIOXIDE (NO2) THESE CAN BE CONVERTED TO SULFURIC ACID AND NITRIC ACID - TWO STRONG ACIDS.

A NARROW RANGE OF pH IS REQUIRED BY MANY BIOLOGICALLY IMPORTANT CHEMICAL REACTIONS.

WHEN THE pH IS OUTSIDE OF THIS RANGE, THESE PROCESSES ARE DISRUPTED.

AT LOW pH, METALS SUCH AS MERCURY AND LEAD BECOME MORE SOLUBLE.

SOURCES OF ACIDS IN SURFACE WATERS:

1. ACID RAIN

2. MINE DRAINAGE

YOU HAVE A COUPLE OF DEFINITIONS OF ACIDS AND BASES.

AN ACID PRODUCES HYDROGEN IONS ON SOLUTION.

A BASE PRODUCES HYDROXIDE IONS ON SOLUTION.

AN ACID HAS A pH LOWER THAN 7.

A BASE HAS A pH GREATER THAN 7.

‘The vapor pressure of a liquid is the equilibrium pressure of a vapor above its liquid (or solid); that is, the pressure of the vapor resulting from evaporation of a liquid (or solid) above a sample of the liquid (or solid) in a closed container.’

http://www.chem.purdue.edu/gchelp/liquids/vpress.html

LOW TEMPERATURE

LIQUID

HIGH TEMPERATURE

LIQUID

TEMPERATURE IS A MEASURE OF THE AVERAGE KINETIC ENERGY OF THE MOLECULES.

THE HIGHER THE TEMPERATURE, THE MORE MOLECULES THAT HAVE THE ENERGY TO ESCAPE FROM THE SURFACE OF THE LIQUID, SO THE HIGHER THE VAPOR PRESSURE.

THE LOWER THE TEMPERATURE, THE FEWER MOLECULES THAT HAVE THE ENERGY TO ESCAPE FROM THE SURFACE OF THE LIQUID, SO THE LOWER THE VAPOR PRESSURE.

A LIQUID BOILS WHEN ITS VAPOR PRESSURE EQUALS THE PRESSURE ABOVE THE LIQUID.

IF YOU PUT A LIQUID UNDER A VACUUM, IT WILL BOIL AT A LOWER TEMPERATURE, AS THE PRESSSURE ABOVE THE LIQUID IS LOWER.

AS YOU GO UP IN ALTITUDE, ATMOSPHERIC PRESSURE DECREASES, SO LIQUIDS BOIL AT LOWER TEMPERATURES AT HIGHER ALTITUDES.

THIS IS WHY FOODS WOULD TAKE LONGER TO COOK AT HIGHER ALTITUDES.

SOLIDS ALSO HAVE A VAPOR PRESSURE.

IT IS LOWER THAN THAT OF LIQUID, BUT IT EXISTS.

ICE, IF LEFT OUTSIDE OR IN A REFRIGERATOR WILL SUBLIMATE OVER A PERIOD OF TIME.