Reactions of acids

• • oxidation is the loss of electrons
  • reduction is the gain of electrons.
• Reactions with metals


  • Reactive metals react with acids forming a salt and releasing hydrogen gas.
  • The metal atoms donate electrons to the H+ ions in the acid solution.
  • The metal atoms are oxidised and the H+ ions are reduced.

  
• Reactions with carbonates

  Carbonates react with acids to produce carbon dioxide, water and a salt.

  
• Reactions with bases and alkalis

  • Acids produce H+ ions when dissolved in water and alkalis produce OH- ions.
  • Acids and alkalis neutralise each other to form water.
  • The other ions present form a salt.

  The ionic equation for the reaction of an acid with an alkali is:

  H+ (aq) + OH- (aq) -> H2O (l)

  
• Acids can react with insoluble bases in a similar way:

  How an acid neutralises an insoluble base:

  2H+ (aq) + O2- (s) -> H2O (l)

  
• Development of acid-base theory (1)

  • Lavoisier came up with the first theory of acids and bases in the 18th century. He didn't know the formulas of compounds like hydrochloric acid but he did know that sulfuric acid had the formula H2SO4 and nitric acid had the formula HNO3.
  • So he proposed that acids had to have oxygen in them. It was later shown that acids like hydrochloric acid (HCl) and hydrogen sulfide (H2S) don't have any oxygen in them at all.
• Development of acid-base theory (2)

  • At the end of the 19th century, a chemist called Arrhenius suggested that acids release protons in aqueous solution, whilst bases release hydroxide ions.
  • He said that when acids and bases react together they form water and a salt. This is true for loads of examples, but doesn't work for bases such as ammonia (NH3), which don't contain any hydroxide ions.
• Development of acid-base theory (3)

  • Bronsted and Lowry came up with their definition of acids and bases independently of one another. It's clearly based on Arrhenius' theory, but broadens the definition of a base to be a proton acceptor.
  • They also came up with the idea that acids and bases react to form conjugate pairs, rather than a salt and water.
  • This definition currently explains most of our observations, so is one of the theories we still use today — around 100 years later.