Acids & Bases

Definition of an acid: An acid is a substance which produces H+(aq) as the only +ve ions in water. Examples : Name of salt HCl hydrochloric acid monobasic chloride H2SO4 sulphuric acid dibasic sulphate HNO3 nitric acid monobasic nitrate CH3COOH ethanoic acid monobasic ethanoate

Properties of dilute acids : 1. Sour taste 2. Litmus turns red , methyl orange turns red, phenolphthalein turns colourless 3. Metals above H in e.c.s. --- give H2 Mg + 2HCl  MgCl2 + H2 4. Carbonates/hydrogencarbonates --- give CO2& H2O K2CO3 + H2SO4  K2 SO4 + CO2 + H2O 5. Neutralize bases: NaOH + HCl  NaCl + H2O 6. Conduct electricity (with mobile ions)

Properties of concentrated nitric acid : 1. As a dilute acid: Mg + 2HNO3  Mg(NO3)2+ H2 K2CO3 + 2HNO3  2KNO3 + CO2 + H2O NaOH + HNO3 NaNO3 + H2O 2. As an oxidizing agent: I. Dilute nitric acid ---gives nitrogen monoxide 3Cu + 8HNO3  3Cu (NO3)2+ 2NO + 4H2O II. Concentrated nitric acid -- gives nitrogen dioxide Cu + 4HNO3  Cu (NO3)2+ 2NO2 + 2H2O

Properties of concentrated sulphuric acid : 1. As a dilute acid: Mg + H2SO4  MgSO4 + H2 K2CO3 + H2SO4  K2SO4 + CO2 + H2O 2NaOH + H2SO4  Na2SO4 + 2H2O 2. As an oxidizing agent: gives sulphur dioxide Cu + 2 H2SO4  CuSO4 + SO2 + 2H2O 3. As a dehydrating agent: removes elements of water C6H12O6  6C + 6H2O 4. As a drying agent -- removes moisture

Definition of a base: A base is a substance which can neutralize an acid to form a salt and water only. Examples : metal oxides ; metal hydroxides CaO calcium oxide Ca(OH)2 calcium hydroxide CuO copper(II) oxide KOH potassium hydroxide ZnO zinc oxide NaOH sodium hydroxide and NH3 ammonia

Alkalis : An alkali is a water-soluble base They give OH– (aq) in water ; pH > 7 e.g. K+ OH– caustic potash Na + OH– caustic soda -- to make bleach, glass, soap Ca 2+(OH–) 2 slaked lime -- to neutralize acid soil NH3 (aq) ammonia solution -- in glass cleaners NH3 + H2O == NH4+ + OH–

Properties of solutions of alkalis : 1. Bitter taste 2. Soapy feel 3. Litmus -- blue, methyl orange -- yellow, phenolphthalein -- pink 3. Neutralize acids -- OH- + H+  H2O 4. Give precipitates with most metal ions: Mn+ + nOH –  M(OH)n Cu(OH)2: pale blue Fe(OH)2: dirty green Fe(OH)3: reddish brown 5. Give ammonia with ammonium ion

The pH scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 [H+] > [OH-] 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 [H+] > [OH-] [H+] < [OH-] acidic alkaline [H+] = [OH-] neutral It is used to show the acidity of a soln.

The pH of Diet Coke is 3.12 3.12

Measurement of pH Methods pH meter 7.00 pH paper pH1 2 pH8 9

Experiment on measuring pH lemon juice acidic 3 vinegar acidic 3 soap 10 alkaline 12 alkaline baking soda aspirin 5 acidic household ammonia 12 alkaline

Test the pH of most common solution - pH panel http://www.miamisci.org/ph/phpanel.html