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chemistry aqa a-level
C21 acids, buffers + bases
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the pH scale is
logarithmic
an
acid
is a
proton donor
a
base
is a
proton acceptor
acid-base
equilibria involve
transfer
of
protons
a strong acid/base is one that
completely dissociates to ions
when in solution
a weak acid/base is one that
partially dissociates to ions
when in solution
the pH scale measures
hydrogen ion concentration
water
slightly
dissociates
K
w
K_w
K
w
is derived from the
equilibrium constant
for the dissociation of
water
the value of
K
w
K_w
K
w
varies with
temperature
the dissociation constant of a
weak acid
is represented by
K
a
K_a
K
a
acid/base titrations involve an
acid/base
being added to a
base/acid
until an
end
point is reached, shown by an
indicator
a pH curve for a titration has the
pH
on the y axis and the
volume of substance added
on the x axis
a buffer solution maintains an approximately constant
pH
despite
dilution
or
addition of small amounts of acid/base
acidic buffer solutions contain a
weak acid
and the
salt of that weak acid
basic buffer solutions contain a
weak base
and the
salt of that weak base
buffer solutions are used for keeping systems
regulated
in nature, as
enzymes
require a specific
pH
otherwise they
denature
the equation for pKa is
pKa = -log(Ka)
the equation for Kw is
Kw = [OH-][H+]
the concentration of OH- ions of a
strong base
is represented by
[OH-]=[XOH]
the equilibrium constant for the dissociation of
water
is represented by
[OH-]=[H+]
the concentration of H+ ions of a
strong acid
is represented by
[H+]=[HA]
the equilibrium constant of a
weak acid
is represented by
Kc = [H+][A-]/[HA]
the equation for pH is
pH = -log[H+]