AND pH Yogini D Lall Buffers are solutions which have the ability to resist changes in acidity and alkalinity Yogini D Lall Acid buffers and basic buffers are two types of synthetic buffers that are produced in the lab ID: 491705
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BUFFERS AND pH
Yogini D. LallSlide2
Buffers are solutions which have the ability to resist changes in acidity and alkalinity.Yogini D. LallSlide3
Acid buffers and basic buffers are two types of synthetic buffers that are produced in the lab.Yogini D. LallSlide4
Acid buffers keep the pH blow 7Yogini D. LallSlide5
Alkaline buffers keep the pH above 7.Yogini D. LallSlide6
ACID BUFFER SOLUTIONSweak acid – ethanoic acid, CH3COOHsalt of acid – sodium ethanoateCH3COOHNaYogini D. LallSlide7
Partial dissociation into ions: CH3COOH(aq) CH3COO-(aq) + H+ (aq) (A)Complete dissociation unit ions: CH3
COOHNa
(
aq
)
CH
3
COO
-
(
aq
)
+ H+ (aq) (B)
Yogini D. LallSlide8
Adding AlkaliOH- (aq) + H+ (aq) H2O (l)The OH- (aq) will remove the H+ (aq) ions and shift equilibrium to the right. This will regenerate more hydrogen to react with further hydroxide. The hydroxide is therefore “mopped up” by the hydrogen ions. In this way pH does not change.
Yogini D. LallSlide9
Adding Acid CH3COO + H+ CH3COOHThis time the buffer has to mop up extra hydrogen ions from the acid. Equilibrium shifts to the left, removing the majority of the added hydrogen ions by the ethanoate ions keeping the pH approximately constant. Yogini D. LallSlide10
ALKALINE BUFFER SOLUTIONSWeak alkali: Ammonium hydroxide NH3OHSalt of alkali: Ammonium chloride, NH3ClYogini D. LallSlide11
Partial dissociation into ions:NH3(aq) + H2O(l) NH 4+(aq) + OH -(aq)ion in solution, most of NH3 is solvated by water only a few reacts with water.
Yogini D. LallSlide12
Compete dissociation:NH4Cl(aq) NH 4+(aq) Cl- (aq) Yogini D. LallSlide13
ADDING ACIDHydrogen ions will be mopped up by hydroxide ion shifting equilibrium to the right causing the pH to remain constant.Yogini D. LallSlide14
ADDING ALKALIHydroxide ions are mopped up by ammonium ions and thus causing the pH to remain constant.Yogini D. LallSlide15
BUFFERS IN BIOLOGICAL SYSTEMS.Cell contents are buffered to provide a suitable pH by a) phosphatesb) hydrogen carbonatec) amino acid, peptides and proteins.Yogini D. LallSlide16
All chemical reactions are enzyme dependent and enzymes can only function at a pH range of 2 units (2-3 pH units) say pH 7.Buffers are also important in industries e.g. Medicines and cosmetics.Yogini D. Lall