pH and Ka Flashcards
define bronsted Lowry acid
an acid is a proton donor
define bronsted Lowry base
a base is a proton acceptor
what is an amphoteric substance
a substance which can behave as either an acid or a base
define a strong acid
an acid which fully dissociates when it dissolves in water (they have weak conjugate bases)
define a weak acid
an acid which only partially dissociates when it dissolves in water (they have strong conjugate bases)
equation for pH
-log [H+]
equation for [H+]
10 ^-pH
equation for Kw (ionic product of water)
Kw = [H+] [OH-]
does neutral always mean pH 7
no
pure water is always neutral as [H+] always equals [OH-]
however when temperature changed, [H+] changes so pH is not constant
pKa equation
-log (Ka)
Ka equation (from pKa)
10 ^ -pKa
Ka equation (using concentrations)
Ka = [H+][A-] / [HA]
define conjugate acid-base pair
two chemical species that are joined by loss or gain of a proton
define monoprotic acid
releases 1 proton per molecule
define diprotic acid
releases 2 protons per molecule
what 2 assumptions do you make in a Ka calculation
1) [H+] = [A-]
2) [HA] initial = [HA] equilibrium
does a weaker acid have a smaller or larger Ka value (and therefore smaller or larger pKa value)
smaller (and therefore larger pKa value)
enthalpy of neutralisation definition
when one mole of water is formed from the neutralisation between an acid and an alkali under standard conditions (298k 100kpa 1moldm-3)
explain why HCl and HNO3 have the same enthalpy change of reaction (2)
- both strong acids, and monoprotic
- same reaction is occurring (H+ + OH- -> H2O)
what is Kw
the ionic product of water
what is Kw at 298K
1.0 x 10^-14
how to find Ka from pH curve
the pH at the half equivalence point
is equal to the pKa value
Ka = 10 ^ -pKa
