ACIDS & BASES  What is an acid?  What is a base?  What is a pH scale and how do we use one?  What is acid rain and the affects of acid rain?

CHEMIST POINT OF VIEW Chemists divide solutions into two groups: depending upon how they dissociate in water!

DISSOCIATE/DISSOCIATION break into ions Acids dissociate in water, producing H + and anions Bases dissociate in water, producing OH - and cations

I FORGOT! WHAT IS AN ION? An ION is a atom that has gained or lost electrons CATIONS = positive ion (atom donated electrons → positive charge) ANION = negative ion (atom stole electrons → negative charge)

DISSOCIATE/DISSOCIATION break into ions Acids dissociate in water, producing H + and anions Bases dissociate in water, producing OH - and cations

pH scale measures concentration of H + ions Acids high [H + ] Bases high [OH - ]

pH scale is LOGARITHMIC Each point is 10x more or less [H+] than the next point Ex. pH 2 concentration of hydrogen ions is 10 times greater than a pH 3

PRACTICE pH readings pH 3 to pH 1 would be a ______ times more acidic pH 1 to pH 3 would be a ______ times more basic pH 3 to pH 1 is ____________ times more acidic?

ACID Characteristics of Acids: Taste sour Reacts with metals to give of H 2 gas pH values= 0 to 6.9 Litmus paper turns red A solution with a high concentration of hydrogen ions [H + ]

BASES Characteristics of Bases: Taste bitter Feel slippery pH values= 7.1 to 14 Litmus paper turns BLUE A solution with a high concentration of hydroxide ions [OH - ] or a low concentration of hydrogen ions (H + )

NEUTRAL A solution that is neither acidic or basic in nature Characteristics of Neutral solutions: [H+] = [OH-] pH is around 7 No set texture, taste, or reactions Taste sweet or oily (may be tasteless) Feel slippery, sticky, or slick May react with metal or chemically smell strong

NEUTRALIZATION  When an acid and base are mixed, the H+ and OH- combind to form water (neutral) strong acid + strong acid = strong acid strong base+ strong acid = neutral strong acid + weak base = weak acid

STRENGHT OF AN ACID OR BASE Depends upon how much it dissociates in water! STRONG acids and bases dissociate completely (all molecules break apart) STRONG acids & bases conduct electricity WEAK acids and bases dissociate partially (only some molecules break up into ions)

pH & WATER Pure water is neutral Sea water is slightly basic Normal rainfall is slightly acidic due to carbon dioxide (CO 2 ) mixing with water vapor forming carbonic acid Acid rain is acidic

ACID RAIN any form of wet precipitation with a pH less than 5.6

ACID RAIN FORMATION Sulfur oxides (SOx) and Nitrogen oxides (NO x ) combine with water vapor to form an acid That acid is release in fog, rain, or snow

WHERE DO SOx and NOx come from? Natural sources: Volcanoes Forest fires Man-made sources Burning fossil fuels in factories Driving vehicles that use gas

In the US, acid rain is worse in Northeast, due to the large number of factories and use of coal to generate electricity.

EFFECTS OF ACID RAIN Harmful to aquatic life & vegetation Harmful to human health Corrodes (causes to break down) stones & metals

WHAT CAN WE DO? Reduce amount of SO x (sulfur dioxide) and NO x (nitrogen oxides) by Filtering pollutants from factories before released into air Using less energy (hence less fuel burnt) Using cleaner fuels Coal that contains less sulfur "Washing" the coal to reduce sulfur content Natural Gas Bio-fuel Using other sources of electricity (i.e. nuclear power, hydro- electricity, wind energy, and solar energy)