Science 9

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Science 9 Unit C Environmental Chemistry

• Topic 3 How do You Spell Relief?

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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.

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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.)

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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.

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pH Chart
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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.

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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.

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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).

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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.

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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, its
  neutralized almost immediately.
• Calcium Hydroxide Sulfuric Acid ------
  Calcium Sulfate Water
• Ca(OH)2 H2SO4 ------ CaSO4 H2O