Importance

Question 1

Normal pH ranges for the blood, urine, gastric fluid and saliva

Answer 1

7.4, 6.0 (4.4 to 8.0), 2.0 and 6.2 to 7.2

Question 2

Why are pH buffers important in living systems

Answer 2

Ensures enzymes and other cellular processes function optimally

Question 3

What are examples of inorganic buffers

Answer 3

Phosphate (buffer reserve in skeleton), bicarbonate (major buffer)

Question 4

What are macromolecules

Answer 4

Amino acid side chains in proteins

Question 5

What influences the ionic properties of weak acids and bases

Answer 5

The hydrogen ion concentration [H+]

pH = -log10[H+]

Question 6

Dissociation of Acids

Answer 6

Acids dissociate to release hydrogen ions

Acid = A substance which in water tends to produce hydrogen ions

Base = A substance which in water tends to combine with hydrogen ions

A (reversible reaction) H+ + B-

Question 7

What is conjugate acid-base pair

Answer 7

The equilibrium equation always involves a conjugate acid-base pair, comprising a hydrogen ion donor (acid) and an acceptor (base)

Question 8

Dissociation of water

Answer 8

H2O <-> H+ + OH-

Question 9

Dissociation of a strong acid

Answer 9

HCL <-> H+ + Cl-

Question 10

Dissociation of a weak acid

Answer 10

H2CO3 <-> H+ + HCO3-

Question 11

What do higher values of Ka represent

Answer 11

That the acid is stronger and the more the reaction is pushed to the right (dissociated)

Question 12

Both reactions in the dissociation of an acid

Answer 12

The forward reaction is balanced by the reverse reaction

Question 13

Ka

Answer 13

An equilibrium is established such that the ratio of the concentrations of H+ and B- to A is constant

Ka = [H+] [B-] / [A]

Question 14

What is the equation called

Answer 14

Henderson-Hasselbalch equation

Question 15

Equation

Answer 15

pH = pKa + log10[B-]/[A]

Question 16

Equation

Answer 16

pH = pKa + log10[B-]/[A]

Question 17

pKa

Answer 17

pKa = -log10Ka

As [H+] increases so does Ka

This means the stronger the acid the larger Ka hence the smaller pKa

Question 18

Indicators

Answer 18

Weak acids or bases which in the ionised form (In-) and unionised form (HIn) show a difference in colour

HIn (colourless) <-> H+ + In- (red)

Question 19

Degree

Answer 19

The degree of ionisation and pH will be related by the equation

pH = pKa + log10[In-] / [HIn]

Question 20

Determination of pH (contd.)

Answer 20

The ratio of [In-]/[HIn] is determined by the pH. This ratio determines the colour

Question 21

Electrical methods

Answer 21

pH meter. Measurement made using a glass electrode (thin-walled glass bulb containing a platinum electrode immersed in 1.0M HCL)

Question 22

Buffer Solutions

Answer 22

Resist pH changes when acid or base added. Consist of a conjugate acid-base pair of either a weak acid or weak base. Buffering systems in the body play a vital role in maintaining homeostasis. Buffering in the mouth limits pH changes due to acid produced by plaque bacteria

Question 23

Plaque

Answer 23

Plaque bacteria ferment dietary carbohydrates to produce acid which causes plaque pH to fall leading to increased solubility of dental enamel which if not reversed, results in dental caries

Question 24

Saliva

Answer 24

Saliva acts as a buffer and neutralises the acid produced thereby (if buffering is adequate) preventing dental caries

Question 25

What does saliva contain

Answer 25

Saliva contains some unusual proteins which are histidine rich and known as histatins. These are important buffers in saliva

Question 26

Buffers in bodies 2

Answer 26

Essential for maintenance of body pH. Bicarbonate is an important buffer in body fluids like the blood