1.2 Acids and Bases

What happened to the forest?

What causes an upset stomach?

Acid Rain "Acid rain" is a broad term referring to a mixture of wet and dry deposition (deposited material) from the atmosphere containing higher than normal amounts of nitric and sulfuric acids. The precursors, or chemical forerunners, of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion.

Effects of Acid Rain Acid rain causes acidification of lakes and streams and contributes to the damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. In addition, acid rain accelerates the decay of building materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's cultural heritage. Prior to falling to the earth, sulfur dioxide (SO2) and nitrogen oxide (NOx) gases and their particulate matter derivatives—sulfates and nitrates—contribute to visibility degradation and harm public health.

So what do we mean by Acid? An acid is a compound that dissolves in water to form a solution with a pH lower than 7. The opposite is a base, a compound that dissolves in water to from a solution with a pH higher than 7. Well what is pH then? pH: is the measure of the percent of hydrogen ions in a solution.

pH That pH scale we talked about is actually a measure of the number of H+ ions in a solution. If there are a lot of H+ ions, the pH is very low. If there are a lot of OH- ions, that means the number of H+ ions is very low, so the pH is high.

pH pH is measured on a scale of 0 to 14. 0 = very acidic 7 = neutral 14 = very basic

Acids cont… Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases. Bases feel slippery, change litmus blue, and become less basic when mixed with acids.

Measuring pH To identify a substance as an acid, a base, or neutral, an indicator is used. It changes color according to the type of substance it is put into. Indicators can be solids, such as litmus paper, or universal indicator (which change color over a wide pH range which can identify many different substances and is more precise), or they can be liquids

A universal indicator is used to measure pH Red litmus paper will turn blue in the presence of a base. Blue litmus paper will turn red in the presence of an acid,

Applications of pH Hot Tubbing!!!!!

Neutralizing Reactions Acids and bases react together when they are mixed. This type of reaction is called neutralization. Both the acid and the base are used up in this type of reaction and a salt and water are produced. Hydrochloric Acid + Sodium Hydroxide --» Sodium Chloride + Water HCl + NaOH ------ » NaCl + H2O

Neutralizing Acid Rain Rainwater is naturally slightly acidic. When this water combines with chemicals in the atmosphere such as sulfur dioxide or nitrogen dioxide, the effect results in Acid Rain (with a pH as low as 3 - in some parts of Canada). To neutralize this acid rain, lime (calcium hydroxide - which is a base) is added to lakes.

Neutralizing Acid Rain Hydroxide + Sulfuric Acid ------ » Calcium Sulfate + Water Ca(OH)2 + H2SO4 ------ » CaSO4 + H2O This is not necessary in Alberta because the mountains contain rich deposits of limestone, making the water naturally basic. When the acid rain falls, it is neutralized almost immediately.