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BDS1 BAMS: Molecules and Cells > Acids, Bases and Buffers > Flashcards

Acids, Bases and Buffers Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is an acid?

A

A molecule or ion which tends to give up protons in solution

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2
Q

What is a base?

A

A molecule or ion which tends to acquire protons in solution

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3
Q

What is Ka?

A

Acid dissociation constant

Direct measure of strength of an acid

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4
Q

What is the acid dissociation constant equation?

A

Ka = [H+].[X-]/[HX]

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5
Q

What does a low pKa mean?

A

The lower the pKa, the stronger the acid

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6
Q

How do you work out pKa from Ka?

A

pKa = -log10Ka

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7
Q

When does a buffer work maximally?

A

When it is half dissociated

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8
Q

What is the pH of water?

A

7

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9
Q

What does a pH < 7 mean?

A

Acidic solution

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10
Q

What does a pH > 7 mean?

A

Basic solution

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11
Q

Which acids do oral bacteria produce when breaking down carbohydrates?

A

Lactic acid, formic acid, acetic acid, propionic acid, butyric acid

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12
Q

What is the pKa of hydrochloric acid?

A

pKa <1

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13
Q

What is the equation for pH?

A

pH = -log10 [H+]

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14
Q

How is carbonic acid formed in the body?

A

When carbon dioxide dissolves in the blood

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15
Q

When is lactic acid formed?

A

During anaerobic respiration - during exercise (in muscle during rapid movement)

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16
Q

What is lactic acid converted to in the liver in the “Cori” cycle?

A

Glucose by gluconeogenesis

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17
Q

Which component of teeth gives enamel its rigidity?

A

Hydroxyapatite

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18
Q

Describe the dissolution of calcium phosphate (hydroxyapatite) by acids

A

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
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19
Q

What is tooth erosion caused by?

A

The direct effect of acids in the diet on teeth

20
Q

What is a chelating agent?

A

Agents which bind strongly to divalent an trivalent cations

21
Q

Which chelating agent is present in orange juice?

A

Citric acid

22
Q

Citric acid is a chelating agent. What does this mean?

A

Chelating agents bind strongly to divalent and trivalent cations. Citric acid binds to Ca2+, preventing remineralisation of teeth

23
Q

What is the definition of a ‘buffer’?

A

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

24
Q

What is a buffer solution made up of?

A

Mixtures of either a weak acid and one of its salts, or a weak base and one of its salts

25
Q

What is the Henderson-Hasselbalch equation?

A

pH = pKa + log10 [base]/[acid]
Allows you to estimate the pH of a buffer/to determine the amount of acid and conjugate base needed to make a buffer solution of a certain pH

26
Q

Within which range does a buffer have effective buffering capacity?

A

Within +/- 1 pH unit of its pKa

27
Q

When do buffers have greatest buffering capacity?

A

When 50% dissociated (pKa = pH)

28
Q

In a buffer, when does pKa = pH

A

When the buffer is 50% dissociated

29
Q

What is the main buffer in saliva?

A

Bicarbonate (HCO3-)

30
Q

Name 3 buffers present in saliva

A
  1. Bicarbonate
  2. Phosphate
  3. Protein
31
Q

Where does bicarbonate in saliva come from?

A

Bicarbonate in saliva comes partly from the blood and partly from the action of carbonic anhydrase, an enzyme in the salivary glands that forms carbonic acid. Carbonic acid dissociates into hydrogen ions and bicarbonate

32
Q

What is the pH of saliva?

A

pH 6.7

33
Q

Which pH does bicarbonate buffer optimally?

A

pH 6.7 - the pH of saliva

34
Q

What do water and carbon dioxide form and which enzyme is involved?

A

Carbonic acid
Carbonic anhydrase catalyses the reaction
H2o + CO2 H2CO3

35
Q

Why does phosphate act as a buffer at 3 different pH ranges?

A

There are 3 different equilibria involved

  1. H3PO4 H+ + H2PO4-
  2. H2PO3 H+ + HPO42-
  3. HPO42- H + PO43-
36
Q

Explain how proteins in the saliva can act as buffer

A
  • Many amino acids in proteins contain side chains which are acidic or basic
  • e.g. aspartic and glutamic acids contain carboxyl groups in their side chains
  • Histidine has an imidazole side-chain with a pKa of 6.0
37
Q

Which protein is an important buffer the saliva?

A

Histatins - rich in histidine

Help to buffer the saliva against the effects of acids

38
Q

What type of proteins are good buffers?

A

Proteins containing acidic or basic amino acids e.g. aspartic acid, glutamic acid, lysine, arginine, histidine

39
Q

What pH is blood maintained at?

A

pH 7.4

40
Q

Why is it important that blood is maintained at a pH of 7.4?

A

Cells require pH in the cytoplasm and organelles to be closely controlled to preserve enzyme and membrane function

41
Q

Which buffers are important in maintaining the pH of blood (pH 7.4)?

A

Bicarbonate and protein buffers

42
Q

What is the pH of saliva?

A

pH 6.7

43
Q

Explain how phosphate acts as a buffer in the saliva in resisting the pH as it becomes more alkaline

A

Phosphate donates H+ ions to resist the increasing alkalinity

44
Q

Explain how phosphate acts as a buffer in the saliva in resisting the pH as it becomes more acidic

A

Phosphate accepts H+ ions as the pH becomes more acidic

45
Q

Which side chain does histidine have which has important buffering capacity in saliva?

A

Imidazole

46
Q

Which amino acids in proteins are the main acidic buffers?

A

Aspartic acid

Glutamic acid

BDS1 BAMS: Molecules and Cells (13 decks)

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