pH and buffering Flashcards
what is pH
measure of H ion conc
acidity or alkalinity of a solution
what does acidity depend on
only on free H+ not those still bound to anions
what is blood pH range
7.35 - 7.45
what is the living blood pH range
7.0 - 7.8
what is it called when blood pH too high and low
alkalosis and acidosis
where do acids come from in the body?
- diet
- breakdown of proteins
- incomplete oxidation of fats or glucose
- loading and transport of CO2 in the blood
how is acid-base balance regulated
by lungs and kidneys
and chemical buffers in the blood
what do buffers do
resist abrupt and large swings in pH by
- releasing H+ when pH rises
- binding H+ when pH drops
what happens when pH rises and pH drops in buffered solution
rises - OH inc
drops - H+ inc
what % of an infant is water
73
in old age what is water % of body mass
45
what is water % of healthy man and woman
60 and 50
why do men have a higher proportion of water than women
women have more fat which is anhydrous
what M is pure water
55.6M
what should a buffer contain
weak acid and its conjugate base
what gives the best buffer
pH at half disscociation
what is Ka
dissociation costan of an acid [H+][A-]/[HA]
what does a large Ka and small pKa value mean
stronger the acid
what is pKa
-logKa
what is the equivalence point
when the two reactants are mixed un exactly the proportions indicated by the equation - equal moles
what is the Henderson-Hasselbach equation
pH= pKa + log [A-]/[HA]
what occurs at pKa
equal amounts of dissociated and non dissociated forms of the acid (conjugate base and acid)
- buffering is best
what are pKa values of
H2CO3 > HCO3-
H2PO4- > HPO42-
6.1 and 6.8
which amino acids are involved in physiological buffering
histidine
- most amino side chains do not buffer in a physiological range
where does glycine buffer
2.3 and 9.6
alpha carboxyl and amino groups are not good physiological buffers
pKa of oxyHb
6.8
pKa of deoxyHb
7.8
changes due to orientation
neighbouring groups affect the pKa
what is critical pH
the highest pH at which there is a net loss of mineral from the teeth
what is the critical pH value
5.5
what does the critical pH depend on
amount of Ca in the saliva
- depends on ionic product of calcium phosphate in saliva
how can we lower critical pH so the tooth could withstand a lower H without demineralising
increasing local concentrations of calcium and/or phosphate
what happens if Ca or phosphate is too high
calcium phosphate in the saliva or plaque fluid becomes destabilised and will precipitate out to form calcus
what is Stephan’s curve
assesses cariogenicity of different food
