acids

• Acid


  A substance that dissolves in water to produce hydrogen ions as the only positive ions
• Acids


  • Colourless solutions
  • Have a sour taste
  • Conduct electricity
  • Corrosive
  • pH value less than 7
  • Blue litmus paper turns red
  • Red litmus paper does not change
• Acid + Metal


  Salt + Hydrogen gas
• Acid + Base (metallic oxide or metallic hydroxide)


  Salt + Water
• Acid + Carbonate


  Salt + Water + Carbon dioxide
• Acid + Hydrogen Carbonate


  Salt + Water + Carbon dioxide
• Hydrochloric acid + Magnesium

  • Magnesium chloride + Hydrogen gas
• Metals below hydrogen in the reactivity series of metals cannot displace hydrogen and therefore do not react with dilute acids (copper + HCl does not react)
• Test for hydrogen gas


  Put a lit splint near the top of a test tube containing hydrogen. The hydrogen reacts with oxygen and explodes, causing a squeaky pop. A colourless, odourless gas was evolved which extinguished a lit splint, test tube felt warm. An exothermic reaction took place
• Test for carbon dioxide

  Carbon dioxide gas is bubbled into calcium hydroxide solution (limewater). CO2 forms a milky precipitate in Ca(OH)2
• Classification of Acids


  • Organic Acids (obtained from natural sources, such as fruits and animal products e.g. lactic, citric, and tartaric acid)
  • Inorganic Acids (Mineral acids prepared from minerals e.g. Hydrochloric acid (HCl), Sulphuric Acid (H2SO4), and nitric acid (HNO3))
• Strong acids


  Completely ionized in aqueous solution (e.g. HCl -> H+ + Cl-)
• Weak acids


  Partially ionised (e.g. CH3COOH)
• Basicity of an acid

  The number of hydrogen (H+) ions that can be produced by one molecule of acid in an aqueous solution
• Basicity of acids


  • Monobasic (liberate 1 hydrogen ion per molecule)
  • Dibasic (liberate 2 hydrogen ions per molecule)
  • Tribasic (liberate 3 hydrogen ions per molecule)
• Basic oxides


  • Formed when metals react with oxygen, usually ionic in nature, Group 1, 2 and lanthanides form basic compounds, large amount of energy released, readily react with water (e.g. M2O3, MO2, ThO2, Na2O + H2O -> 2NaOH)
• Acidic oxides


  • Formed when non-metals react with oxygen, covalent bonds, low melting and boiling point (except B2O3 and SiO2), can be called acid anhydrides (e.g. NO, CO2, SO3 + H2O -> H2SO4, B2O3 + H2O -> 2H3BO3)
• Amphoteric oxides


  • Exhibit both acidic and basic characteristics, react with acids to form water and salt (exhibiting basic property), react with alkalis to form salt and water (exhibiting acidic property) (e.g. Al2O3)
• Neutral oxides


  • Do not exhibit acidic nor basic characteristics (e.g. NO, CO)