Top2-Ch2-P58-66EndReverse

Question 22

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

Answer 22

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

Question 23

• 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)

Answer 23

Titration curve of acetic acid, explain?

Question 24

• 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.

Answer 24

A handy rule of thumb for understanding the pH log scale

Question 25

• pH
• True

Answer 25

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

Question 26

large

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

Answer 26

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

Question 27

pH 7.2

buffers

Answer 27

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

Answer 28

The pH of the lysosome lumen is maintained at

Question 29

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

Answer 29

What are buffers?

Question 30

pH

Answer 30

Buffers resist changes in

Question 31

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

Answer 31

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

Question 32

1 pH unit either side pKa value
pKa = maximal buffering

Answer 32

Buffers only work if both forms are present, ie.

Question 33

• 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

Answer 33

See picture of blue part which is buffering

Question 34

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

Answer 34

A buffer system is?

Question 35

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

Answer 35

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

Question 36

equal; H+ and OH-; absorb

Answer 36

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

Question 37

phosphate
proteins

Answer 37

Name two Intracellular buffers:

Question 38

bicarbonate

Answer 38

Name an extracellular buffer

Question 39

pH, pKa, and buffer concentration

See formula below

Answer 39

Henderson-Hasselbach equation expresses the relationship between ?

State the formula

Question 40

Answer 40

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)]

Question 41

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

Answer 41

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;

Question 42

1. energy
2. release of energy

See diagram below of formation of ATP

Answer 42

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

Question 43

condensation reactions

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

Answer 43

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.