pH and Buffers

Question 1

Definition of pH

Answer 1

Measure of H+ conc that are free in a solutionq

Question 2

Definition of buffers

Answer 2

Weak acid + conjugate base
can resist abrupt and large pH changes in the body fluids by releasing H+ when pH in creases, binding H+ when pH decreases

Question 3

Definition of a strong acid

Answer 3

H+ completely dissociates in solution

Question 4

Definition of a strong base

Answer 4

OH- completely dissociates in solution

Question 5

Definition of a weak acid

Answer 5

H+ partially dissociates in solution

Question 6

Definition of a weak base

Answer 6

OH- partially dissociates in solution

Question 7

Definition of ionization of water

Answer 7

Process by which water splits into their H+ and OH- in solution

Question 8

Definition of Ka

Answer 8

Acid dissociation constant, greater the constant, the stronger the acid, smaller the constant, the weaker the acid

Question 9

Definition of pKa

Answer 9

pH at which the acid is half dissociated, same amount of undissociated acid and conjugate base.

Question 10

Why is blood pH maintained

Answer 10

In contact with nearly every body cell

Acidosis/alkalosis can occur is not maintained

Question 11

Living range and regulated pH levels

Answer 11

7. 0-7.8

7. 35-7.45

Question 12

Where does acids in the body come from

Answer 12

By food
Protein breakdown
incomplete oxidation of fats/glucose
Loading/transport of CO2 in blood

Question 13

How is the acid base balance regulated

Answer 13

Lungs (ventilation)
Kidney (monitor and adjust blood pH)
Chemical buffers

Question 14

Buffer operation

Answer 14

When pH too high, H+ released

When pH too low, H+ binds

Question 15

Range of buffer operation

Answer 15

1-2

Question 16

Water content of humans

Answer 16

Infants=73%
Healthy male=60%
Healthy female=50%
Old age=45%

Question 17

Conc of pure water

Answer 17

55.6M

Question 18

Keq equation

Answer 18

[H+]/[H2O] = Keq

[1.0 x 10-7]/[55.6] = 1.8 x 10-14

Question 19

Kw equation

Answer 19

[H+][OH-] = Kw = 1.0 x 10-7

Question 20

How to calculate pH and [H+]

Answer 20

-log[H+] = pH
10-pH = [H+]

Question 21

Analyzing titration curves

Answer 21

Mid point of horizontal section = pKa
pKa = pH at which the buffer is strongest
Midpoint = midpoint between total and 0 dissociation

Question 22

How to calculate pKa and Ka

Answer 22

pKa = -log(Ka)

Question 23

Henderson-Hasselbalch equation

Answer 23

pH = pKa + log [A-]/[HA]

Question 24

Physiologically important buffers

Answer 24

Saliva
H2CO3 => HCO3-
H2PO4- => HPO4 2-
Protein + => protein

Question 25

Amino acids and buffers on titration

Answer 25

NH3+ and COO- has pKa values

No buffering at zwitterion

Question 26

Amino acids involved in buffering

Answer 26

Histidine (pKa at 6) and cysteine

Question 27

How can haemoglobin be a buffer

Answer 27

Hb has many histidine residues, within physiological pH

Question 28

Change of pKa of a group

Answer 28

Histidine pKa in Hb has different pKa to free His

Neighboring groups affect pKa

Question 29

How does oxyhemoglobin and deoxyhaemoglobin affects buffers

Answer 29

Deoxy, greater pKa than Oxy, better buffer

Greater difference between deoxy pKa and blood pH when carbonic acid conc is high, absorbs H+ as weaker acid than oxy

Question 30

Lipid soluble molecules and diffusion at different pH

Answer 30

When lipids are charged, cannot pass through membrane at certain pHs

Question 31

Dissociation of AA as pH increases

Answer 31

NH3+ fully protonated
COO- NH3+
COO- fully deprotonated