12.1 Flashcards
an acid is a proton…
donor
a base is a proton…
acceptor
when does a molecule which contains hydrogen act as an acid
if the hydrogen carries a slightly positive charge
what makes a molecule a base
it must contain a lone pair in order to form a dative covalent bond
what is a conjugated acid-base pair
consists of either a base and its conjugate acid or an acid and its conjugated base
state the conjugated pairs for this reaction
HCl + H2O <=> H3O+ + Cl-
Cl- & HCl
H2O & H3O+
what is meant by monoprotic
a species that can donate 1 proton
what is meant by diprotic
a species that can donate 2 protons
what is an amphoteric substance
one that can act both as an acid and as a base
how do you define a strong acid
one that almost completely dissociates in aqueous solutions
how do you define a weak acid
one that only partially dissociates in aqueous solutions
what is the equation for pH
pH = -log[H+]
what does Ka stand for
acid dissociation constant
what is the general equation for Ka
Ka = [H+(aq)] [A-(aq)] / [HA(aq)]
what is the equation for Ka in strong acids
Ka = [H+(aq)] / [HA(aq)]
what is the equation for pKa
pKa = -logKa
How does pKa and Ka effect the pH of an acid
as Ka increases pH decreases
as pKa decreases pH decreases
what is the equation for self-ionization of water
Kw = [H+(aq)] [OH-(aq) / [H2O(l)]
How is the equation for ionisation of water simplified at a stated temperature
Kw = [H+(aq)] [OH-(aq)]
what does Kw stand for
the ionic product of water
how do you define a neutral solution
one in which the hydrogen ion concentration is equal to the hydroxide ion concentration
what is the equation for pKw
pKw = -log Kw
why do even the most alkaline solutions still contain some hydrogen ions
because of the fact that water self-ionises
how can the relative strengths of different acids or bases be determined
by measuring the pH of equimolar aqueous solutions of the acids/bases, at the same temperature
what is the pH of a salt formed from a strong acid and a strong base
7
what is the pH of a salt formed from a weak acid and a strong base
> 7
what is the pH of a salt formed from a strong acid and a weak base
<7
what is the pH of a salt formed from a weak acid and a weak base
dependent on the relative strengths of the acid and base
how is pH effected when a strong acid is diluted by a factor of 10
pH increases by a factor of 1 for each 10-fold decrease in concentration
how is pH effected when a weak acid is diluted by a factor of 10
pH value increases by a factor of about 0.5 for each 10-fold decrease in concentration
how can Ka of a weak monobasic acid such as benzoic acid by determined experimentally
accurately weigh between 0.4-0.5g of the acid
dissolve it in roughly 50cm^3 of deionised water
transfer solution to a 250cm^3 volumetric flask and add washings from the beaker using deionised water to make the solution up to the mark
mix by inverting the flask then withdraw a sample and use a calibrated pH meter to measure the pH of the solution
then caluclate the Ka value
what are the issues with calculating Ka experimentally
you must assume that the concentration of the acid at equilibrium is identical to the original concentration of the acid however it is not as it may have dissociated slightly
the accuracy of the measurement of pH as this largely effects the Ka calculated due to small amounts being used
