Acids and Bases

||  ACIDS
Uses
Domestic – orange juice, vinegar
Industry to produce a range of products (fertilisers, drugs, explosives and plastics)
Environmental Damage
Acid rain – corrosion of buildings (stone, marble, steel)
Threat to aquatic life – Carbonic acid forms as CO2 dissolves in H2O, causing oceans/lakes to become acidic.
Properties
Change the colour of some indicators
Litmus paper goes red
Corrosive
Taste sour
React with bases
Molecular in structure
Low pH
Examples
Hydrochloric acid
Sulphuric acid
Carbonic acid
lactic acid
ascorbic acid
phosphoric acid
hydrochloric acid

||  BASES
Uses
Effective cleaners – react with fats/oils to produce water soluble soaps
Antacids
Fertilisers and explosives
Common Lab Acids
•              ammonia NH3
•              sodium hydroxide NaOH
•              hydrochloric acid (HCl)
•              Calcium hydroxide Ca(OH)2
•              sulphuric acid (H2SO4)
•              nitric acid (HNO3)
•              Calcium oxide CaO
•              Lead oxide PbO
Environmental Damage
Acid rain – corrosion of buildings (stone, marble, steel)
Threat to aquatic life – Carbonic acid forms as CO2 dissolves in H2O, causing oceans/lakes to become acidic.
Properties
Change the colour of some indicators
Litmus paper goes blue
Taste bitter
Caustic
Slippery feel
Relatively high pH
React with acids, causing neutralisation
Generally ionic compounds/salts
Alkali – a water soluble base

||  SAFTEY
Equipment
Safety glasses, lab coats and clearly label bottles
Why?
Ionisation/hydrolysis of acids is energy releasing (exergonic).
Heat is formed.
Always add acid to water, slowly, small amount of acid to lots of water.

||  INDICATORS
Use
Change different colours in the presence of an acid or base

Common indicators
•              Methyl Orange
•              Phenolphthalein
•              Litmus
•              Universal indicator (mixture of many indicators)

||  Brønsted Lowry Theory
Definition
•              Acids – Substances that donate a proton/hydrogen ion (H+)
•              Bases – Substances that accept a proton/hydrogen ion
Example
Take HCl and water:
         HCl (g) + H2O (l) →      H3O+ (aq) + Cl-(aq)
        Acid         base       Conjugate acid / base  
•              HCl donates proton to H2O - acid
•              H2O accepts proton from HCl - base
Explanation
•              The definition of an acid as a proton donor and a base as proton acceptor means that bases become the mirror companion of acids, merely simple receptors
•              The measurement of hydronium ion concentration become key to the defining the degree of acidity.
•              Bases à accept hydrogenà become conjugate acids
•              Acids à donate hydrogenà become conjugate base
Conjugate Acid base pair
Differ by one transferable H+ ion

||  REACTIONS
Ionisation
A reaction in which a substance reacts with water to produce ions.
      HCl(g) + H2O à H3O+ (aq) + Cl- (aq)
            A chloride and hydronium ion is produced
Hydrolysis
A reaction involving the addition of water, to form OH- or H3O+ ions
Dissociation of bases
Ionic bases separate into constituent ions. Do not ionise as the do not react with water to produce ions as acids do.
Neutralisation
When an acid and base react to produce a salt and water.



Hydronium ion
Occurs when water gains an extra hydrogen. A 4th hydrogen is never added as this would be too unstable.
water responds to the other substance, if the other is an acid, it becomes a base and vice versa
Deionised water
[H3O+] = 10-7
[OH-] = 10-7
+ lots of H2O
Amphiprotic substances
Substances that can act as an acid or a base
Depends whether the solute present is an acid or a base
•              If the solute is a stronger acid, the substance will act as a base
•              If the solute is a stronger base, the substance will act as an acid
When an amphiprotic substance is placed in water, it reacts as an acid and a base.
Diprodic acid
Example
HSO4-
HSO4- (aq) + H2O (aq) → H2SO4 (aq) + OH- (aq) >7
HSO4- (aq) + H2O (aq) → SO42- (aq) + H3O+ (aq) <7

Although both reactions will be happening simultaneously, one reaction will occur to a greater extent. We can identify the dominant reaction by measuring the pH of the solution.
HCO3, H2O,
pH Measurement
Measure the [H3O+] = 10-7 or [OH-] = 10-7 not the other acid/base products (they are a kind of spectator ion)

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