Topic 8 - Acids & Bases

Acid: substance that ionises in water to produce H+ Alkali: soluble base that ionises in water to produce OH- All alkalis are bases but not all bases are alkali.

the rxn between NH3 and HCl gas can’t be explained, as NH3 doesn’t contain OH- NH3 (g) + HCl (g) -> NH4Cl (s)

Acid: proton (H+) donor Base: proton (H+) acceptor In an aq soln, a proton can be represented as either hydrogen (H+) or hydronium (H3O+)

when a water molecule forms a coordinate bond with a proton

• monoprotic: donates 1 proton eg. HCl • diprotic: donates 2 protons eg. H2SO4 • triprotic: donates 3 protons eg. H3PO4

• the acid/base is weak as they don’t fully dissociate e.g. CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq) CH3COOH: BL acid H3O+: conjugate acid

if it’s a backwards rxn instead of forwards, the conjugate base will act as a base

• conjugate acids and bases will differ from one another by a single proton • they are called conjugate acid-base pairs

species that can act as either BL acid or BL base depending on the rxn e.g. HCO3 - (aq) + H2O (l) CO3 2- (aq) + H3O+ (l) HCO3 - (aq) + H2O (l) H2CO3 (aq) + OH- (aq)

acts as an acid in the presence of a strong base by donating a proton, and vice versa for strong acids eg. H2O

Acid: must be able to dissociate and release H+ Base: must be able to accept H+ (have lone e- pair) Amphiprotic: must possess both a lone e- pair and a H+ ion

• amphiprotic specifically related to BL theory (where emphasis is on proton transfer) • amphoteric has a broader meaning, describing a substance that can act as both acid & base even in rxns that don’t involve proton transfer

• metal oxides/hydroxides • ammonia • soluble carbonates • hydrogen carbonates

because of its oxidising properties

Acid + metal -> salt + H2

acid + base -> salt + water

enthalpy change occurring when an acid and base react together to form 1 mol of water for all strong acids & bases, enthalpy change is very similar: ΔH = -57 kJ/mol

acid + carbonate -> salt + H2O + CO2

colourless

red

red

sour

bitter

blue