Acids, bases and salts

• How can carbon dioxide gas be identified?

  Passing it through limewater, which will turn milky.
• How can you test for the presence of carbonate ions?

  If carbon dioxide is produced when a solution is added to an acid, it must contain carbonate ions.
• Acids and alkalis that are dangerous are stored in containers which have hazard warning labels to show they are corrosive.
• Litmus turns red in acids and blue in alkalis.
• Indicators are substances that change colour when added to acids and alkalis.
• Solutions with a pH less than 7 are acidic.
• Solutions with a pH of 7 are neutral.
• Solutions with a pH greater than 7 are alkaline.
• Universal indicator gives an approximate measure of the pH of a solution. A more accurate value can be obtained using a pH probe.
• When added to a neutral solution, universal indicator is green in colour.
• All acids ionise when they dissolve in water, releasing hydrogen ions (H+).
• The presence of hydrogen ions in a solution makes it acidic.
• Bases are chemically opposite to acids.
• Some bases are soluble in water and dissolve to form alkalis.
• The presence of OH- ions in a solution makes it alkaline.
• Acids react with alkalis in neutralisation reactions.
• acid + alkali → salt + water
• For all neutralisation reactions, the H+ ions from an acid react with the OH- ions from an alkali to form water.

  The ionic equation for the reaction is written:

  H+(aq) + OH-(aq)​ → H2O(l)
• Number of moles = mass (g) / Mr
• Hydrogen gas is identified using a lit splint which produces a squeaky pop sound.
• The reactions of metals with acids are exothermic, which means they give out heat.
• When acids react with metals, they produce a salt and hydrogen gas.
• acid + metal → salt + hydrogen
• Insoluble bases are usually metal oxides.
• When acids react with metal oxides, they produce a salt and water.
• acid + metal oxide → salt + water
• When acids react with metal carbonates, they produce a salt, water and carbon dioxide gas.
• The salt produced when magnesium reacts with hydrochloric acid is magnesium chloride.
• The salt produced when potassium hydroxide reacts with sulfuric acid is potassium sulfate.
• The salt produced when copper(II) carbonate reacts with nitric acid is copper(II) nitrate.
• The salt produced when calcium oxide reacts with ethanoic acid is calcium ethanoate.
• The salts produced from nitric acid all have names that end in nitrate.
• The salts produced from sulfuric acid all have names that end in sulfate.
• Sodium sulfate is the name of the salt produced when sodium hydroxide reacts with sulfuric acid.
• Reactivity series: (most to least reactive)

  • potassium
  • sodium
  • magnesium
  • aluminium
  • carbon
  • zinc
  • iron
  • tin
  • lead
  • copper
  • silver
  • gold