Acids, bases + salts

Acids, bases + salts

1. Acids and bases

   • Acids
     • Hydrochloric acid
       • HCl
     • Common acids
       • Sulfuric acid
         • H2SO4
       • Nitric acid
         • HNO3
     • Everyday acids
       • Ethanoic acid
         • CH3COOH
       • Methanoic acid
         • HCOOH
       • Citric acid
         • C6H8O7
     • When added to water, releases H+ ions -> solution
       • H+ = active ingredient in acids
         • Responsible for all acid reactions
     • Proton donor
   • Bases
     • Common bases
       • Metal oxides - MgO, CuO
       • Hyrdroxides - NaOH, Mg(OH)2
       • Ammonia - NH3
       • Amines
     • Opposite of an acid
       • Proton acceptor
       • Neutralises acids
   • Alkalis
     • Any chemical compound that gives a solution with pH greater than 7.0 when dissolved with water
     • Common alkalis
       • Sodium hydroxide - NaOH
       • Potassium hydroxide - KOH
       • Ammonia - NH3
     • Very corrosive
     • Special type of base that dissolves in water -> aqueous hydroxide ions OH-
       • In solution, OH- neutralise H+ from acids - water
     • Ammonia = gas that dissolves in water -> weak alkaline solution
       • Weak base as only small % of dissolved NH3 reacts

2. Salts

   • Ionic compound
     • Cation = usually a metal ion or ammonium ion
     • Anion = a salt derived from an acid
     • Formula = same as parent acid but H+ replaced by positive ion
   • Acid salts
     • 2 replaceable H+ ions = diprotic acid
     • One H+ replaced -> acid salt
     • Acid salt can behave as acid, as other H+ can be replaced to form conventional salt
   • Formation of salts
     • Produced by neutralising acids with carbonates, bases, alkalis
     • Acid + carbonate -> salt, water and CO2
       • See bubbles of CO2
     • Acid + base -> salt + water
       • See solid dissolve
     • Acids + alkali -> salt and water
     • Reaction of reactive metals and acids
   • Ammonium salts and fertilisers
     • Used as artificial fertislisers
     • Formed when acids = meutralised by aqueoous ammonia
     • Contain ammonium ion NH4+

3. Water of crystallisation

   • Compounds can't be crystallised if water isn't present
   • Empirical formula of compund = separated by water of crystallisation by a dot
   • Relative no. of water molecules of crystallisation shown after dot
   • Can work out the formula using % or mass compositions
     • Additional final step to show water separately in dot formula
   • Use no. of H atoms to work out no. of water molecules of crystallisation
     • Oxygen may be split between H2O molecules and ions
   • Determine the formula by heating it so that water is driven off and evaporates
     • Need to find mass of hydrated salt, mass of anhydrous salt, mass of water in hydrated salt
     • 1) Calculate amount, in mol, of anhydrous salt
     • 2) Calculate amount, in mol, of water
     • 3) Determine formula of hydrated salt