Top2-Ch2-P58-66End

Question 1

1. Titration is used to ?
2. Equilibrium is when

Answer 1

1. determine the amount of acid in solution through the addition of known concentration of base (usually NaOH) until equilibrium
2. [HA] = [A-] (shown by indicator dye or pH meter), the pH at this point is also the pKa

Question 2

Titration curve of acetic acid, explain?

Answer 2

• As NaOH is introduced, the added OH- combines with the free H+ in solution, forming H2O.
• As free H+ is removed, HAc further dissociates to satisfy its equilibrium constant until finally all that is left is conjugate base (pH7)
• When exactly 50% of the NaOH has been added, 50% of the original acetic acid has dissociated
• When [HAc] = [Ac-], the pH = the pKa of acetic acid (4.76)

Question 3

A handy rule of thumb for understanding the pH log scale

Answer 3

• pH is a log scale.
• At pH=pKa, the [HA]:[A-] ratio is 1:1
• At one pH unit from pKa, the ratio is 1:10
• At 2 pH units from pKa, the ratio is 1:100
• i.e. if pKa =4.76, at pH 6.76 acetic acid is 99% ionised
• At pH 2.76 it is ≈99% protonated.

protonated is addition of proton to atom, molecule or ion.

Question 4

• Almost all biological processes are __ dependant.
• Most enzymes have optimal activities in the compartments where they function. True or False

Answer 4

• pH
• True

Question 5

Small changes in pH produce _____ changes in the rate of biochemical reactions. Give an example.

Answer 5

large

Eg. Structure of protein dependant on ionic state as determined by pH of surrounding medium

Question 6

Most cells maintain the pH of the cytoplasm at approximately ____ and to do so it uses _____

Answer 6

pH 7.2

buffers

Question 7

The pH of the lysosome lumen is maintained at

Question 8

What are buffers?

Answer 8

Are aqueous systems that tend to resist changes in pH when small amounts of acid (H⁺) or base (OH^-) are added.

Question 9

Buffers resist changes in

Answer 9

pH

Question 10

In mixtures of weak acids and conjugate base eg. acetic acid/acetate, then acid is (explain) and base is (explain)

Answer 10

• *Acid** = reservoir of potential protons ready to counteract rises in pH
• *Base** = proton acceptor to counteract falls in pH

Question 11

Buffers only work if both forms are present, ie.

Answer 11

1 pH unit either side pKa value
pKa = maximal buffering

Question 12

See picture of blue part which is buffering

Answer 12

• The blue area is the buffering region for acetic acid
• The buffer effect is approximately linear for 1 pH unit each side of the pKa
• i.e. over 2 pH units

Question 13

A buffer system is?

Answer 13

• a weak acid (proton donor) and
• its conjugate base (proton acceptor).

Question 14

1. For acetic acid the pKa is ____ and the buffering region is between _________ .
2. so at the buffer region you can add either _____ or _____ to the solution with little effect to pH

Answer 14

1. For acetic acid (pKa 4.76) and buffering region: pH 3.76 - 5.76
2. acid or base

Question 15

At the pKa you have ____ amounts of acid and base and so have enough ____ and ____ to ____ incoming acid or base

Answer 15

equal; H+ and OH-; absorb

Question 16

Name two Intracellular buffers:

Answer 16

phosphate
proteins

Question 17

Name an extracellular buffer

Answer 17

bicarbonate

Question 18

Henderson-Hasselbach equation expresses the relationship between ?

State the formula

Answer 18

pH, pKa, and buffer concentration

See formula below

Question 19

Calculate the pH of a solution containing 0.1 M acetic acid and 0.2 M acetate ion, given that the pKa of acetic acid is 4.76. [Be able to perform such calculations for minitests (Calculators permitted)]

Answer 19

Question 20

So, water is an important solvent in which biological reactions occur, but it can also act as a reactant

Chemical reaction involving water are generally of two kinds;

Answer 20

1. Hydrolysis reaction: cleavage (splitting of chemical bonds) + addition of water
2. Condensation reaction: formation of a compound + release of water

Question 21

1. Condensation, requires ____
2. Hydrolysis is the reverse which is the ____ __ ____

Answer 21

1. energy
2. release of energy

See diagram below of formation of ATP

Question 22

1. The linking of sugars, nucleotides and amino acids to form their respective polymer macromolecules occurs by _____ ______
2. The monomers left are called _____ . Give an example.

Answer 22

condensation reactions

“residues”, E.g. amino acid residues in proteins