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)

Comments

Post a Comment

Popular posts from this blog

Common Literary Techniques in Tim Winton's 'The Turning'

Common techniques in Winton’s The Turning . Most of these examples are taken from ‘Aquifer’. Direct, concrete images: ‘In the afternoon the blue bush plain was hazy with smoke and the dust churned up with bulldozers.’ While these descriptions are simple and clear ways of describing the real world, Winton often highlights aspects that explore and reveal key aspects of the ideas or characters he is exploring. For example, the ‘hazy’ and ‘churned up’ elements in this description highlight 2 things: 1) the confused and often conflicting feelings of the narrator as he reflects back on a time of emotional and hormonal turmoil (growing up); 2) the murky and muddled interaction between past and present.  There is a tension or irony here in that the descriptions seem so straightforward and clear that the memories are certain, solid, can’t be argued with, which is true.  And yet how one grapples with these memories, how one mixes them/reconciles them with the present...
Read more

Ionic Compounds

Image
Ionic Bonding: occurs between a metal and a non-metal results in a positive cation (metal) and a negative anion (non-metal) forms a salt, that is a lattice structured crystal that is more stable than the reactants Electron Transfer Diagrams Used to represent a reaction, showing the transfer of electrons Reactants on the left, products on the right Ionic Lattice: ionic compounds form crystals, a lattice composed of positive and negatively charged atoms in a regular 3D structure. They are held together by strong electrostatic attraction between oppositely charged ions. The atoms are packed in a regular repeating pattern. They form into the most stable arrangement with oppositely charged ions as close as possible and those with the same charge, as far away as possible. Properties Rigid as ions are tightly held Does not conduct electricity- no free charged particles in solid state, however, in molten or aqueous they are able to as ions have...
Read more

Electrons

Image
Exciting Electrons: Every element emits light if it is heated. This is because the atom has absorbed energy, and then loses it in the form of light. The light can be separated to form an Electron Emission Spectrum. Each line on the EES corresponds to a particular frequency of light being given off by an atom; therefore each corresponds to one exact amount of energy being emitted. Emission Spectrum from various elements Niels Bohr proposed an explanation for the ES, stating that electrons of specific eneergy move around the nucleus in orbits or energy levels, and cannot exist between these levels. When given excess energy (from flame or electric current) electrons are able to move to a higher obit. this is from ground state (lowest energy level) to an excited state . As the electron moves back to ground state, the amount of energy given off is the difference in energy between the levels, and is given off as a photon of light. In an ionic compound, it is the anion (negatively ...
Read more