Acids and Alkalis

• Reaction between acid and metal

  Salt + hydrogen
• Reaction between acid and metal oxide


  Salt + water
• Reaction between acid and metal hydroxide

  Salt + water
• Reaction between acid and metal carbonate


  Salt + water + carbon dioxide
• Metal oxides


  Normally bases rather than alkalis because they are normally insoluble, while alkalis are soluble bases
• Magnesium sulfate


  Salt formed from magnesium and sulfuric acid
• Zinc nitrate


  Salt formed from zinc oxide and nitric acid
• Calcium chloride


  Salt formed from calcium carbonate and hydrochloric acid
• Methyl orange


  Red in acid, yellow in alkali
• Blue litmus paper


  Turns red in acid, stays blue in alkali
• Red litmus paper


  Stays red in acid, turns blue in alkali
• Acids in aqueous solution

  Produce H+ ions
• Bases in aqueous solution

  Produce OH- ions
• Acids and bases in terms of proton transfer

  Acids are proton donors, bases are proton acceptors
• Reaction between hydrochloric acid and ammonia

  HCl + NH3 → NH4Cl
• Reaction between sulfuric acid and sodium hydroxide

  H2SO4 + 2NaOH → Na2SO4 + 2H2O
• Strong and weak acids

  Strong acids are completely ionised, weak acids are only partially ionised
• Strong and weak bases

  Strong bases are completely ionised, weak bases are only partially ionised
• pH scale


  Used to quantify the relative acidity and alkalinity of a solution
• Measuring pH


  Universal indicator, pH probe
• pH values


  Acid: pH < 7, Neutral: pH = 7, Alkali: pH > 7
• Importance of controlling soil acidity

  If too acidic, crops will be unable to grow
• Acidic oxide


  Generally formed when a non-metal reacts with oxygen, e.g. SO2
• Basic oxide


  Generally formed when a metal reacts with oxygen, e.g. CaO
• Neutral oxide


  Some non-metallic oxides are neutral and can't neutralise acids or bases, e.g. H2O
• Amphoteric oxide


  Some metal oxides can neutralise both acids and bases, e.g. Al2O3
• Removing a soluble salt from a reaction mixture

  Add excess base, filter out unreacted base, evaporate to leave salt crystals
• Preparing a soluble salt from an acid and soluble base

  Use acid/base titration to find exact volumes, react exact quantities, evaporate to leave salt crystals
• Collecting an insoluble salt from a reaction mixture

  Filter the precipitate, wash with distilled water, dry to leave salt crystals
• Magnesium nitrate


  Salt formed from magnesium and nitric acid
• Sodium sulfate


  Salt formed from sodium hydroxide and hydrochloric acid
• Sodium hydroxide + calcium ions


  White precipitate
• Sodium hydroxide + chromium(III) ions

  Green precipitate
• Producing sodium sulfate from sodium hydroxide and hydrochloric acid

  Titration
• Precipitate formed when sodium hydroxide reacts with aluminium ions


  White precipitate at first, re-dissolves with excess NaOH to form a colourless solution
• Precipitate formed when sodium hydroxide reacts with zinc ions


  White precipitate at first, re-dissolves with excess NaOH to form a colourless solution
• Observation when ammonia reacts with aluminium ions


  White precipitate forms
• Observation when ammonia reacts with calcium ions


  No observations
• Observation when ammonia reacts with zinc ions

  White precipitate forms at first, re-dissolves in excess ammonia
• Carrying out a flame test

  1. Clean a nichrome wire using hydrochloric acid

  2. Turn the Bunsen burner onto the blue flame

  3. Dip the wire in the solid substance that you want to test

  4. Place the wire in the flame. Record the colour of the flame