eLFH - Acid and Bases

Question 1

At which pH do most body enzymes function optimally

Answer 1

At normal pH of intracellular and extracellular compartments

Question 2

Intracellular pH

Answer 2

7.0

Question 3

Extracellular pH

Answer 3

7.4

Question 4

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

Answer 4

Proteases in stomach

Question 5

Acid definition examples

Answer 5

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

Question 6

Base definition examples

Answer 6

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

Question 7

pH equation

Answer 7

Question 8

pH indicator definition

Answer 8

Chemicals which change colour when put into acids or bases

Change in H+ ion concentration changes their spectral properties

Question 9

Examples of pH indicators

Answer 9

Litmus
Phenolphthalein
Methyl orange
Methyl red

Question 10

Complete dissociation definition

Answer 10

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

Question 11

Strong ion definition

Answer 11

Ions that are completely dissociated in aquesous solution

Question 12

Examples of strong ions in biological solution

Answer 12

Cations:
Na+
K+
Ca2+
Mg2+

Anions:
Cl-
SO4 (sulphate 2-)
Lactate

Question 13

Weak ion definition

Answer 13

Compounds which dissociate incompletely

Question 14

Example of weak ion

Answer 14

Carbonic acid with incompletely dissociates into bicarbonate and H+ ions

Question 15

Dissociation constant (K)

Answer 15

Rate of forward reaction when partial dissociation occurs

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

Question 16

Strong acid definition

Answer 16

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

Question 17

Strong acid example

Answer 17

Hydrochloric acid
HCl -> H+ + Cl-

Lactic acid also behaves as a strong acid

Question 18

Weak acid definition

Answer 18

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

Question 19

Equation for dissociation constant of an acid A

Answer 19

Question 20

Strong base definition

Answer 20

Fully dissociates in aqueous solution into component cation and hydroxyl ion

Question 21

Example of strong base

Answer 21

Sodium hydroxide

NaOH -> Na+ + OH-

Question 22

Weak base definition

Answer 22

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

BH+ is cation of the base B

Question 23

Examples of weak bases

Answer 23

Ammonia

Many local anaesthetics including lidocaine

Question 24

Equation for weak base dissociation constant Kb

Answer 24

Question 25

pK definition

Answer 25

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

Question 26

Henderson-Hasselbalch equation

Answer 26

Question 27

Henderson-Hasselbalch equation for carbon dioxide and bicarbonate equilibrium

Answer 27

Substitute HA for CO2 Substitute A- for HCO3- Then replace CO2 as: [CO2] = PCO2 x solubility CO2

Question 28

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

Answer 28

6.1

Question 29

Buffer definition

Answer 29

Solutions able to resist changes in the concentration of H+ and OH- Commonly solutions of weak acids (and less commonly weak bases)

Question 30

How do weak acids act as buffers

Answer 30

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

Question 31

Main buffer systems in human body to maintain normal pH

Answer 31

Bicarbonate buffer system Phosphate buffer system Proteins

Question 32

Bicarbonate buffer system

Answer 32

Question 33

Phosphate buffer system

Answer 33

Question 34

Protein buffer system

Answer 34

Question 35

The pH glass electrode

Answer 35

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

Question 36

The pH glass electrode circuit components

Answer 36

Question 37

Why is body temperature important for accurate blood pH measurement

Answer 37

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