Acids - Summary

Acids

Disciplinary Ideas

  • Acids contain H atoms that release H+ ions in water.
  • Acid-base reactions involve the transfer of H+ ions from an acid to a base.

Learning Objectives

  • Define acids in terms of ions produced in aqueous solutions and their effect on Universal Indicator.
  • Describe neutrality, relative acidity, and alkalinity:
    • Relative H^+ and OH^− ion concentrations.
    • Color in Universal Indicator.
    • The pH scale.
  • Describe characteristic properties of acids in reactions with metals, bases, and carbonates to form salts.
  • Describe neutralization reaction: H^+ + OH^− → H_2O.
  • Describe the importance of controlling pH in soils and treating excess acidity with calcium hydroxide.
  • Classify oxides as acidic, basic, amphoteric, or neutral.

Examples of Acids

  • Mineral acids:
    • Hydrochloric acid (HCl)
    • Nitric acid (HNO_3)
    • Sulfuric acid (H2SO4)
  • Organic acids:
    • Citric acid (C6H8O_7)
    • Ethanoic acid (CH_3COOH)

Properties of Acids

  • Sour taste.
  • Turn blue litmus paper red; Universal Indicator orange or red.
  • pH less than 7.
  • Conduct electricity in aqueous solutions.
  • Acids show their properties in the presence of water
  • Acids produce H^+ when dissolved in water.

Chemical Properties of Acids

  • Acids react with metals to produce salt and hydrogen gas.
  • Acids react with metal carbonates to produce salt, water, and carbon dioxide gas.
  • Acids react with bases (metal hydroxide / metal oxide) → salt + water

Chemical Reactions of Acids

  • Acid + Metal → Salt + Hydrogen gas
    • Example: 2HCl + Mg → MgCl2 + H2
    • Test for Hydrogen: Use a lighted splint; it extinguishes with a pop sound.
  • Acid + Metal Carbonate → Salt + Water + Carbon Dioxide gas
    • Example: 2HNO3 + Na2CO3 → 2NaNO3 + H2O + CO2
    • Test for Carbon Dioxide: Pass gas into limewater; a white precipitate forms.
  • Acid + Base (Metal Hydroxide / Metal Oxide) → Salt + Water
    • Example: H2SO4 + 2NaOH → Na2SO4 + 2H_2O
    • Example: H2SO4 + MgO → MgSO4 + H2O

Uses of Acids

  • Food stuffs: carbonic acid in fizzy drinks, acetic acid in vinegar, citric acid in fruit juices
  • Electrolyte in car batteries: sulfuric acid
  • Manufacture of soaps and detergents: sulfuric acid

Acids & the Environment

  • Factories burning coal liberate sulfur dioxide gas (SO_2).
  • Burning petrol in car engines produces oxides of nitrogen (NO_2).
  • SO2 and NO2 dissolve in rainwater to form acid rain.
  • Acid rain lowers the pH of water, corrodes metals and buildings, and removes essential minerals from the soil.