eLFH - Acid and Bases Flashcards

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1
Q

At which pH do most body enzymes function optimally

A

At normal pH of intracellular and extracellular compartments

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2
Q

Intracellular pH

A

7.0

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3
Q

Extracellular pH

A

7.4

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4
Q

Examples of enzymes which work optimally at different pH to intra/extracellular pH

A

Proteases in stomach

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5
Q

Acid definition examples

A

A substance which:
- dissociates in water to form H+ ions
- donates a proton to a solution
- is a potential acceptor of an electron pair

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6
Q

Base definition examples

A

A substance which:
- accepts a H+ ion
- dissociates in water to form hydroxide ions

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7
Q

pH equation

A
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8
Q

pH indicator definition

A

Chemicals which change colour when put into acids or bases

Change in H+ ion concentration changes their spectral properties

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9
Q

Examples of pH indicators

A

Litmus
Phenolphthalein
Methyl orange
Methyl red

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10
Q

Complete dissociation definition

A

Characteristic of compounds with ionic bonds - e.g NaCl
#
Dissociates completely in aqueous solution into its component sodium ions and chloride ions

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11
Q

Strong ion definition

A

Ions that are completely dissociated in aquesous solution

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12
Q

Examples of strong ions in biological solution

A

Cations:
Na+
K+
Ca2+
Mg2+

Anions:
Cl-
SO4 (sulphate 2-)
Lactate

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13
Q

Weak ion definition

A

Compounds which dissociate incompletely

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14
Q

Example of weak ion

A

Carbonic acid with incompletely dissociates into bicarbonate and H+ ions

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15
Q

Dissociation constant (K)

A

Rate of forward reaction when partial dissociation occurs

Governs proportion of molecular and ionic compound i.e carbonic acid molecules and bicarbonate ions

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16
Q

Strong acid definition

A

Acid which completely dissociates into H+ ions and the anion of the acid

17
Q

Strong acid example

A

Hydrochloric acid
HCl -> H+ + Cl-

Lactic acid also behaves as a strong acid

18
Q

Weak acid definition

A

Does not completely dissociate in solution
Acid and ions are in equilibrium

19
Q

Equation for dissociation constant of an acid A

A
20
Q

Strong base definition

A

Fully dissociates in aqueous solution into component cation and hydroxyl ion

21
Q

Example of strong base

A

Sodium hydroxide

NaOH -> Na+ + OH-

22
Q

Weak base definition

A

Only partially dissociates in aqueous solution
Reacts with water molecules to generate hydroxyl ions in equilibrium

BH+ is cation of the base B

23
Q

Examples of weak bases

A

Ammonia

Many local anaesthetics including lidocaine

24
Q

Equation for weak base dissociation constant Kb

A
25
Q

pK definition

A

pK of a substance is the pH at which a weak acid or base exists in its ionised and unionised forms to an equal degree

pKa = pK for a weak acid
pKb = pK for a weak base

26
Q

Henderson-Hasselbalch equation

A
27
Q

Henderson-Hasselbalch equation for carbon dioxide and bicarbonate equilibrium

A

Substitute HA for CO2
Substitute A- for HCO3-

Then replace CO2 as:
[CO2] = PCO2 x solubility CO2

28
Q

pKa for reaction CO2 + H2O <-> H+ + HCO3-

A

6.1

29
Q

Buffer definition

A

Solutions able to resist changes in the concentration of H+ and OH-

Commonly solutions of weak acids (and less commonly weak bases)

30
Q

How do weak acids act as buffers

A

Addition of H+ to the solution shifts dissociation equilibrium to the left ‘mopping up’ some additional H+

31
Q

Main buffer systems in human body to maintain normal pH

A

Bicarbonate buffer system

Phosphate buffer system

Proteins

32
Q

Bicarbonate buffer system

A
33
Q

Phosphate buffer system

A
34
Q

Protein buffer system

A
35
Q

The pH glass electrode

A

Hydrogen ion sensitive glass

Solutions containing different concentrations of H+ and therefore pH are placed either side of this glass creating a potential difference

pH on one side kept constant using buffer solution

Electrical circuit used to measure pH of test solution on other side e.g blood in gas machine

36
Q

The pH glass electrode circuit components

A
37
Q

Why is body temperature important for accurate blood pH measurement

A

pH electrode is calibrated and maintained at 37 degrees Celsius

Dissociation of acids and bases increases as temperature rises

Therefore if body temp lower than 37 degrees a correction must be made for an accurate pH at patient’s body temp