Acid/Base/Buffers

Question 1

The modified H-H equation for the bicarbonate system

is:

Answer 1

pH = 6.1 + log ( [HCO3-] mM ) / (.03 x Pco2 mmHg)

Question 2

What is [HCO3-] in the blood under normal conditions?

Answer 2

24 mM

Question 3

What is PCO2 in the blood under normal conditions?

Answer 3

40mmHg

Question 4

What is [CO2] dissolved in the blood under normal conditions?

Answer 4

1.2 mM

Question 5

Normal arterial blood pH:

Answer 5

7.34-7.44

Question 6

Normal venous blood ph:

Answer 6

Normal venous blood ph: 7.28-7.42 (lower due to higher [CO2])

Question 7

Describe the law of mass action [le Chatelier’s principle]:

Answer 7

For any reversible reaction, the forward and reverse rates of the reaction are directly dependent on the concentrations of the reactants and the products respectively.

ie: in A B, if you increase the concentration of A, the rate of A -> B goes up. If you increase the concentration of B, the rate of B -> A goes up instead.

Equilibrium constant (Keq) = [products] / [reactants].

Question 8

pH is the: (formula and written description)

Answer 8

negative log of the proton concentration in a solution.

pH = -log[H+]

In neutral solutions, [H+] = 1 x 10-7; log [H+] = -7, negative log = 7. So a small change in pH means a big chance in H+, which is tough for our bodies to manage.

Question 9

Ka measures:

pKa is:

Answer 9

Ka measures the tendency of a weak acid to dissociate in water.

pKa is the negative log of Ka for a given weak acid.

Question 10

The lower the pKa, the_____ the acid

The higher the pKa, the ___ the acid

Answer 10

stronger (more proton donation in water)

weaker (more proton acceptance in water)

Question 11

Write the Henderson-Hasselbalch (H-H) equation for any given weak acid or base:

Answer 11

pH = pKa + log ([A-]/[HA]).

Question 12

When pH = pKa, what is true?

Answer 12

when pH = pKa, the concentrations of deprotonated and protonated acid are equal.

(ie: when pH = pKa, the acid is half deprotonated and half protonated.)

Question 13

In what range does maximum buffering occur?

Answer 13

Plus or minus 1 pH unit from the pKa of the acid/base.

Question 14

_____ is the only amino acid side chain that protonates or deprotonates at physiological pHs- thus important for acid-base balance in body.

Answer 14

Histidine

Question 15

Higher levels of CO2 in the blood ____ the blood’s pH. This is because you make more _____, which drives the______ of carbonic acid to form ______.

Answer 15

lower; carbonic acid; deprotonization; bicarbonate + a proton (These extra protons float around in the blood and lower the pH.)

Question 16

When pH < pKa by 1 pH unit, what % of products remain protonated? What about at 2 pH units below pKa?

Answer 16

10% remain deprotonated. (90% are protonated). At 2 pH units, less than 1% remain deprotonoated (99% protonated).