A1 Preparation of Buffers

Question 1

The participant in many biochemical reactions and makes up about 70 % of human body and other animals.

Answer 1

Water

Question 2

The H+ concentration of an aqueous solution may affect what? (4)

Answer 2

Conformation and structures of substances

Concentration of molecular and charged species

Affect the transport of substances through membranes

Efficiency of enzyme

Question 3

Mechanisms that prevent the sudden variation of H+ concentration (3)

Answer 3

Buffer systems of the body

Action of kidneys in which acids and bases are excreted in the urine

Respiratory mechanisms regulate H+ ion concentration is regulated by the rate of CO2 elimination in the lungs

Question 4

Resists drastic changes in H+ concentration when small amounts of acid or base are added

Widely employed in the laboratory to control pH of culture media for microorganisms and tissues

Used for many chemical reactions requiring controlled pH including those catalyzed by Enzymes

Answer 4

Buffer solution

Question 5

A buffer can be made out of which combinations (2)

Answer 5

weak acids and their salts (acetic acid + sodium acetate)

weak bases and their salts (ammonia + ammonium chloride)

Question 6

Body fluids and their buffer systems: Blood Plasma

Answer 6

7.4

HCO3(-1)/H2CO3,

HPO4(-2)/H2PO4(-)

Question 7

Body fluids and their buffer systems: Red Blood Cells

Answer 7

7.2

HCO3(-1)/H2CO3

Hb(-)/HHb

HbO2(-)/HHbO2(-)

Question 8

Body fluids and their buffer systems: Spinal fluid

Answer 8

7.4

HPO4(-2)/H2PO4-

Proteinate(-)/H PRoteins

HCO3(-)/H2CO3

Question 9

Body fluids and their buffer systems: Urine

Answer 9

4.8 - 7.4

HPO4(-2)/H2PO4(-)

Org.acid(-)/H Org. acid

Question 10

Industrial processes which use buffers: (5)

Answer 10

fermentation, electroplating, leather, photographic materials, dyes

Question 11

Steps to produce a buffer solution from a weak acid and its salt: (5)

Answer 11

1. Choose weak acid with pKa closest to desired pH(ensures max buffer capacity)
2. Consider concentration of salt and acid for buffer capacity. Concentration (0.05 to 0.50 M) Buffer capacity (0.01 to 0.10)
3. Use Henderson-Hasselbach equation to calculate ratio of salt and weak acid to obtain required pH (only for 4 to 10)
4. Mix volumes of acid and salt

5 Check pH

Question 12

Commonly used buffer acids: Acetic acid

Answer 12

pKa1: 4.74

Question 13

Commonly used buffer acids: Carbonic acid

Answer 13

pKa1: 6.1
pKa2: 10.4

Question 14

Commonly used buffer acids: Citric acid

Answer 14

pKa1: 3.1
pKa2: 4.7

Question 15

Commonly used buffer acids: Phosphoric acid

Answer 15

pKa1: 2.14
pKa2: 7.2
pKa: 12.4