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Acids and Bases Buffers BIOB111 Session 6 (Buffer (keeps the pH within…
Acids and Bases
Buffers
BIOB111 Session 6
Arrhenius
Acid-Base
Theory
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Arrhenius
Acid
water ionises the Arrhenius acid (breaks covalent bond)
result = cation (+) + anion (-)
a hydrogen containing compound that in H2O produces H+
HCL → H+ (cation) + Cl- (anion)
Arrhenius
Base
water dissociates the base (breaks the ionic bond)
result = cation (+) + anion (-)
a hydroxide containing compound that in H2O produces OH-
KOH → K+ (cation) + OH- (anion)
Ionisation (acid) and
Dissociation (base)
splits compounds (ionic and covalent) into individual ions
the production of ions from a molecular compound that has been dissolved in solution
Brønsted-Lowry
Acid-Base Theory
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Brønsted-Lowry
Base
a proton (H+ ion) acceptor
has a conjugate acid
Brønsted-Lowry acid and base production
must occur simultaneously
.
You cannot have one without the other
Brønsted-Lowry
Acid
has a conjugate base pair
a proton (H+ ion) donor
Conjugate
Acid-Base
Pairs
for most acid-base reactions, 100% H+ transfer doesn't occur
equilibrium is reached = forward and reverse reactions occur simultaneously
2 acids and bases involved in 2 conjugate acid-base pairs
an acid and a base that differ from each other through the loss or gain of a proton H+
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Classification
of acids
Proticity
acids can be classified by the number of H+ they can transfer per molecule during an acid-base reaction
Monoprotic acid
supplies 1 H+ per molecule
Diprotic acid
supplies 2 H+ per molecule
Triprotic acid
supplies 3 H+ per molecule
Strength
of acids
Strong
acid
stable, unreactive conjugate base
the more +ve the acid the more readily it will donate H+
yields a
weak conjugate base
ionisation equilibrium lies far to the right
transfers almost 100% of it's protons to water
Weak
acid
ionisation equilibrium lies far to the left
yields a
stronger conjugate base
transfers only a small % of it's protons to water
unstable, reactive conjugate base
the more -ve the acid the less readily it will give donate H+
the
stronger
the acid, the
weaker
the conjugate base
the
weaker
the acid, the
stronger
the conjugate base
Strength
of bases
Strong
base
yields a
weak conjugate base
stable, unreactive conjugate base
ionisation equilibrium lies far to the right
the more -ve the base the more readily it will accept H+
Groups IA and IIA on periodic table
gives up OH- easily
dissociates almost completely in water
Weak
base
ionisation equilibrium lies far to the left
yields a
stronger conjugate base
gives up OH- with difficultly
unstable, reactive conjugate base
does not dissociate completely in water
the more -ve the base the less readily it will accept H+
the
stronger
the base, the
weaker
the conjugate acid
the
weaker
the base, the
stronger
the conjugate base
Neutralisation
reactions
salt and water are the products
chemical reaction between an acid and a hydroxide base
Self-ionisation
of water
at equilibrium the concentrations of H+ and OH- are equal
exist as a combination of H3O+ and OH- ions
a very small percentage of water molecules in pure water interact
pH
scale 0 - 14
indicates the acidity (<7) or alkalinity (>7) or a solution
Buffer
keeps the pH within optimal desired values
buffers in bodily fluids are able to neutralise H3O+ and OH-
maintaining specific pH range in different body compartments is vital to adequate body function
an aqueous solution, composed of two compounds: a weak acid and it's stronger conjugate base
the weak acid part of the buffer neutralises the added base
the stronger conjugate base part of the buffer neutralises the added acid
Electrolyte
compounds that can conduct electricity in aqueous solution
acids, bases and salts
Strong
complete dissociation into ions within H2O
strong acid or strong base
Weak
does not completely dissociate in H2O
weak acid or weak base
