acids, bases and pH (A2) Flashcards
what is a bronsted-lowry acid?
a species that donates a proton
what is a bronsted-lowry base?
a species that accepts a proton
what is a conjugate acid-base pair?
two species which can be interconverted by transfer of a proton
e.g. HCl (aq) <—–> H+ (aq) + Cl- (aq)
conjugate acid: HCl
Conjugate base: Cl-
what is a monobasic acid?
an acid which has one hydrogen atom that can be replaced e.g HCl, CH3COOH, HNO3
what is a dibasic acid?
an acid which has two hydrogen atoms that can be replaced e.g. H2So4
what is a tribasic acid?
an acid which has three hydrogen atoms that can be replaced e.g H3PO4
redox reactions with acids and metals ionic and word equation
acid + metal —–> salt + hydrogen
e.g. zinc
2H+(aq) + Zn(s) ——> Zn2+ (aq) + H2(g)
neutralisation reactions between acids and carbonates ionic and word equation
acid + carbonate —> salt + water + carbon dioxide
e.g. solid copper carbonate
2H+(aq) + CuCO3(s) —> Cu2+(aq) + H2O(l) + CO2(g)
aqueous sodium carbonate (ionic)
2H+ (aq) + CO3 2- (aq) —–> H2O (l) + CO2(g)
neutralisation reactions between acids and metal oxides ionic and word equation
acid + base —> salt + water
e.g. magnesium oxide
2H+(aq) + MgO(s) —-> Mg2+(aq) + H2O(l)
neutralisation reactions between acids and alkalis ionic and word equation
acid + alkali ——> salt + water
H+(aq) + OH-(aq) —-> H2O(l)
how do you calculate Ka? (acid dissociation constant)
[H+][A-] / [HA]
what is the general equation for the dissociation of a weak acid?
HA(aq) <——> H+(aq) + A-(aq)
what are the units of Ka?
mol dm-3
how do you calculate pKa from Ka?
pKa = -logKa
how do you calculate Ka from pKa?
10 to the power of -pKa
what is the relationship between Ka/pKa and acid strength?
the stronger the acid, the larger the Ka value and the smaller the pKa value
the weaker the acid, the smaller the Ka value and the larger the pKa value
what is the expression for calculating pH using [H+]?
pH = -log[H+]
what is the expression for calculating [H+] using pH?
[H+] = 10 to the power of -pH
what is the expression for the ionic product of water, Kw?
[H+][OH-] = 1 x 10 to the power of -14
how do you calculate the pH of strong acids?
in aqueous solution, a strong monobasic acid, HA, will completely dissociate
HA(aq) —–> H+(aq) + A-(aq)
this means [H+] = [HA], so pH can be calculated directly from the conc. of the acid
expression for calculating pH of weak acids
[H+] = √Ka[HA]
then use pH = -log[H+]
expression for calculating pH of strong bases
[H+] = Kw / [OH-]
then use pH = -log[H+]
what are the approximations used in calculations involving weak acids?
- [H+]eqm ~ [A-]eqm
(negligible dissociation of H2O) - [HA]eqm = [HA]start
([HA]start»[H+]eqm)
