Science 9 – Unit C: Environmental Chemistry

Topic 3: How do You Spell Relief?

I. Acids

Acids – Taste sour, are soluble in water, and undergo similar chemical reactions to each other, and have a pH less than 7.

Eg. Sulfuric Acid – An acid used in used in car batteries, paints, and industrial processes.

Eg. Phosphoric Acid – An acid used in fertilizers, detergents, and flavouring of foods.

II. Bases

Bases – Taste bitter, are soluble in water, feel slippery, react with acids, and have a pH of more than 7.

Eg. Sodium Hydroxide – Base used in household cleaners such as bleach and in making electronic circuit boards.

Eg. Aluminum Hydroxide – Used in antacid tablets. (Antacid means against acids which is exactly what a base is.)

III. Neutral Substances

Neutral – Substances that are neither acidic nor basic and that have a pH of 7.

Eg. Water, many substances insoluble in water.

pH Chart

Measuring acidity/alkalinity

Acidity = strength of the acid. Alkalinity = strength of the base The pH scale is a way of comparing the

relative acidity or alkalinity of a substance. 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 they can be liquids, such as phenol red.

Neutralization 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. A salt and water are produced.

HCl acid in your stomach has a pH of 2 making it a strong acid. This acid helps in the digestion of food and kills off bacteria. If you eat too quickly, or are under stress, your stomach produces an excess amount of acid (giving you heartburn). To neutralize the excess acid, an antacid tablet is swallowed. This antacid is a mild base.

The pH of Acids

Acidity is measured on the pH scale with anything below 7 being acidic. A decrease of one unit indicates the acidity has been multiplied by a factor of 10. Periods of extreme acidity (like in the spring when the acid snow melts and the acidic water enters the waterways) are called acid shock. Concentrations of chemical indicators are usually measured in parts per million (ppm).

Acid Precipitation/Acid Rain Sulfur, nitrogen, carbon dioxide and carbon

monoxide are emitted from industry and automobiles as byproducts. They are released into the air and react with water vapour in the sky forming acid rain. This was a major problem in the 80s.

These acids then come back to the ground as acid precipitation (with a precipitation lower than the pH of normal rain ~5.6) and have a variety of negative effects such as destroying wetland ecosystems, making soil infertile, wrecks historic buildings.

Neutralizing Acid Rain Lime, (Calcium hydroxide) is a base;

therefore in many parts of the world lime is added to lakes and soil to counter the acidity of rain. This is not necessary in Alberta because the mountains contain rich deposits of limestone, making the water naturally basic. When acid rain falls, it’s neutralized almost immediately.

Calcium Hydroxide + Sulfuric Acid ------ » Calcium Sulfate + Water

Ca(OH)2 + H2SO4 ------ » CaSO4 + H2O