Acids and Bases

 Acids and bases  Dissociation of water into hydrogen and hydroxide ions.  pH is related to the concentration of hydrogen and hydroxide ions in pure water, acids and alkalis.  Neutralisation  Titrations

 Water contains hydrogen and hydroxide ions.  H 2 O (l) H + (aq) + OH - (aq) 99% 1%  Hence why water is covalent but conducts electricity  A small percentage of water actually exists as Hydrogen and Hydroxide Ions

 In pure water ◦ [H + ] = [OH - ] ◦ The concentration of hydrogen ions equals the concentration of hydroxide ions ◦ Hence why water has a pH of 7

 In ACIDIC solutions ◦ [H + ] > [OH - ] ◦ The concentration of hydrogen ions is greater than the concentration of hydroxide ions

 pH less than 7  Contain more Hydrogen ions (H + ) than hydroxide ions (OH - )  When diluted ◦ Concentration of H + ions decreases ◦ pH INCREASES towards 7

 In ALKALINE solutions ◦ [H + ] < [OH - ] ◦ The concentration of hydroxide ions is greater than the concentration of hydrogen ions.

 pH greater than 7  Contain more hydroxide ions (OH - ) than Hydrogen ions (H + )  When diluted ◦ Concentration of OH - ions decreases ◦ pH DECREASES towards 7

 A neutralisation reaction is where an acid is neutralised by a base resulting in a neutral solution.  A base is a substance which can neutralise an acid ◦ Metal Oxides e.g. MgO CaO ◦ Metal Carbonates e.g. CaCO 3, BaCO 3 ◦ Metal Hydroxides e.g. NaOH, Mg(OH) 2

NameFormula Hydrochloric acidHCl Nitric acidHNO 3 Sulphuric acidH 2 SO 4

Acid + Metal Salt + Water Hydroxide Acid + Metal Oxide Salt + Water  Acid + Metal Salt + Water + CO 2 carbonate

 Ending comes from the Acid ◦ Hydrochloric = Chloride salt ◦ Nitric = Nitrate Salt ◦ Sulphuric = Sulphate Salt  Beginning comes from the Metal part of base NameFormula Hydrochloric acidHCl Nitric acidHNO 3 Sulphuric acidH 2 SO 4

 Lithium hydroxide + Hydrochloric acid  Calcium hydroxide + sulphuric acid  Potassium hydroxide + nitric acid  Ammonium hydroxide + hydrochloric acid  Sodium hydroxide + carbonic acid

 Lithium chloride + water  Calcium sulphate + water  Potassium nitrate + water  Ammonium chloride + water  Sodium carbonate + water

Acid will be measured in burette Alkali in pipette (10cm 3 )

Rough titration 1 st titration 2 nd titration Initial burette reading (cm 3 ) Final burette reading (cm 3 ) Titre (cm 3 ) Average Titre (1 st + 2 nd ) (cm 3 )

 If 25cm 3 of HCl is neutralised by 50cm 3 NaOH (0.2mol/l), what is the concentration of the acid? HCl + NaOHNaCl + H 2 O

 They watch the reaction and do not take part ◦ They are exactly the same on the reactant and product side. ◦ Same state, same number, same charge

Precipitate = a solid Precipitation reaction is when two solutions (aq) are reacted together and an insoluble product is formed – a solid (s) Easily identified by state symbols (aq) + (aq)  (s) + (aq)