Acids, Buffers and Bases Flashcards
What is an acid?
A molecule or ion which tends to give up protons in solution;
water itself: H2O <—> H+ + OH- (a very weak acid)
acetic acid: CH3COOH <—> H+ + CH3COO-
H+ is actually H30+
What is a base?
A molecule or ion which tends to acquire protons in solution:
X- + H+ HX
hydroxyl ion: OH- + H+ <—> H2O
acetate ion: CH3COO- + H+ <—> CH3COOH
ammonia: NH3 + H+ <—> NH4+
amines: R-NH2 + H+ <—> R-NH3+
What is the conjugate acid and what is the conjugate base in this reaction?
HX <—> H+ + X-
Con. Base- X-
Con. Acid- H+
What is the acid dissociation constant?
How to calculate pKa from Ka?
pKa= -logKa
Relationship between pKa and acid strength?
The lower the value of pKa the stronger the acid, The HIGHER the value of Ka the stronger the acid
Name 3 Important acids in biology?
Carbonic Acid
Lactic Acid
Hydrochloric Acid
Describe carbonic acid in biology;
Eqn?
pKa?
How is it formed?
Function/Role?
Carbonic acid: H2CO3 <—> H+ + HCO3-
pKa = 6.37
-Formed when CO2 dissolves in blood tissue fluids.
-Acts as a buffer at physiological pH.
Describe Lactic Acid acid in biology;
Eqn?
pKa?
How is it formed?
Causes?
Lactic acid: CH3CH(OH)COOH <—> H+ + CH3CH(OH)COO-
pKa = 3.86
-Formed by human cells from glucose during anaerobic respiration, especially in muscle during rapid movement.
-Causes cramp.
-Is converted to glucose by gluconeogenesis in the liver (the “Cori cycle”).
In what conditions are acids produced by bacteria?
Anaerobic Conditions
Give some acids produced by oral bacteria and their pKa
Lactic acid: CH3CH(OH)COOH pKa = 3.86
Formic acid: HCOOH pKa = 3.75
Acetic acid: CH3COOH pKa = 4.73
Propionic acid: CH3CH2COOH pKa = 4.87
Butyric acid: CH3CH2CH2COOH pKa = 4.82
Describe the dissolution of calcium phosphate (hydroxyapatite) by acids
-Ca10(PO4)6 (OH)2 + 8 H+ <—> 10 Ca2+ + 6 HPO42- + 2 H2O
-Ca10(PO4)6 (OH)2 + 14 H+ <—> 10 Ca2+ + 6 H2PO4- + 2 H2O
An increase in [H+] causes the equilibrium to shift to the right, increasing the solubilisation of calcium phosphate
An increase in calcium or phosphate concentration causes the equilibrium to shift to the left, inhibiting solubilisation and promoting re-mineralisation
Saliva contains calcium and phosphate to aid remineralisation
Calcium-containing foods such as milk help to protect teeth from decay
Describe Hydrochloric Acid;
Eqn?
pKa?
Role?
HCl <—> H+ + Cl-
pKa = <1
-Secreted into the stomach as part of the digestive process.
-Major component in gastric use
What acid of the acids produced by oral bacteria is produced in the largest numbers?
Lactic Acid
How do oral bacteria produce acids?
By fermenting carbohydrates (mainly dietary)
What does excess amounts of the acids produced by oral bacteria cause?
Tooth decay
-Excess amounts of these acids that are not removed in the oral cavity following fermentation of dietary sugars and carbohydrates by oral bacteria, will cause dental caries if not cleared by saliva
What does calcium assist?
Remineralisation process by shifting equilibrium to the left
What does dental caries occur due to?
The production of acid by plaque bacteria
What is tooth erosion caused by?
The direct effect of acids in the diet on teeth