Acids, Bases and Buffers Flashcards
What is an acid?
A molecule or ion which tends to give up protons in solution
What is a base?
A molecule or ion which tends to acquire protons in solution
What is Ka?
Acid dissociation constant
Direct measure of strength of an acid
What is the acid dissociation constant equation?
Ka = [H+].[X-]/[HX]
What does a low pKa mean?
The lower the pKa, the stronger the acid
How do you work out pKa from Ka?
pKa = -log10Ka
When does a buffer work maximally?
When it is half dissociated
What is the pH of water?
7
What does a pH < 7 mean?
Acidic solution
What does a pH > 7 mean?
Basic solution
Which acids do oral bacteria produce when breaking down carbohydrates?
Lactic acid, formic acid, acetic acid, propionic acid, butyric acid
What is the pKa of hydrochloric acid?
pKa <1
What is the equation for pH?
pH = -log10 [H+]
How is carbonic acid formed in the body?
When carbon dioxide dissolves in the blood
When is lactic acid formed?
During anaerobic respiration - during exercise (in muscle during rapid movement)
What is lactic acid converted to in the liver in the “Cori” cycle?
Glucose by gluconeogenesis
Which component of teeth gives enamel its rigidity?
Hydroxyapatite
Describe the dissolution of calcium phosphate (hydroxyapatite) by acids
Ca10(PO4)6(OH)2 + 8H+ 10Ca2+ + 6HPO42- + 2H2O
- 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
What is tooth erosion caused by?
The direct effect of acids in the diet on teeth
What is a chelating agent?
Agents which bind strongly to divalent an trivalent cations
Which chelating agent is present in orange juice?
Citric acid
Citric acid is a chelating agent. What does this mean?
Chelating agents bind strongly to divalent and trivalent cations. Citric acid binds to Ca2+, preventing remineralisation of teeth
What is the definition of a ‘buffer’?
A solution which resists changes in pH when an acid or alkali is added to it/compounds that resist pH changes when exposed to extremes of pH
What is a buffer solution made up of?
Mixtures of either a weak acid and one of its salts, or a weak base and one of its salts