1. P. Acid-Base Balance

Question 1

pH

Answer 1

pH is defined as the negative logarithm of hydrogen ion [H+] concentration.

The pH scale is in a reciprocal relationship with [H+].

Every 1 unit change in pH represents a 10-fold change in hydrogen ion concentration.

Because the pH scale is based on negative logarithms, lower the pH value higher the [H+].

Question 2

pH of water

Answer 2

H2O  ↔  H+ + OH-
Keq= ([H+][OH-]) / [H2O]
=conc of prods/conc of reacs
[H2O] Keq = [H+][OH-]
-[H2O] Keq= constant

ion-product constant for water
Kw= 1x10^-14 = [H+][OH-]
since conc of [H+] and [OH-] are equal in pure water, 14= pH+pOH
pH=7

There is always water present, hence in this equilibrium equation we can ignore the concentration of water.

The equilibrium constant (Keq)
The concentration of ions is extremely small, so the concentration of H2O remains essentially constant.

Question 3

Acids and bases

Answer 3

An acid donates protons 
An acid (HA) after donating proton becomes the conjugate base (A-)
HA  ↔  H+ + A-

A base accepts protons
A base (A-) after accepting proton becomes the conjugate acid (HA)

Question 4

Strong and weak acids and bases

Answer 4

Strong acids and bases dissociate completely in water
-HCl (a strong acid), NaOH (a strong base)

Weak acids and bases, in contrast, dissociate incompletely in water

• Acetic acid, Lactic acid (weak acids)
• NH3 (a weak base)

Question 5

Henderson-Hasselbalch (HH) equation

Answer 5

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

It’s the relationship between the pH of a solution and the relative amounts of the protonated (acid) and deprotonated (base) forms of a compound.
pH > pKa : More A- than HA
pH = pKa : [A-] = [HA]
pH < pKa : More HA than A-
**(Note: HH equation applies only to 
weak acids and not to strong acids)

Question 6

Buffers

Answer 6

(pic)
A buffer is a mixture that resists changes in pH

The mixture of a weak acid (protonated) and its conjugate base (deprotonated) constitutes a buffer

• Acetic acid (CH3CO2H) and acetate
• H2CO3 and HCO3- (H2CO3=carbonic acid; HCO3-= carbonate ion)
• NH4+ (ammonia) and NH3 (ammonium ion)

Buffering capacity is highest at pH values within ± 1 unit from the pKa
eg Titration of  
a weak acid with a strong base
NaOH -> Na+ + OH-
OH- + CH3COOH -> CH3COO- + H2O

Question 7

Application of HH equation to CO2/Bicarbonate buffer system

& Derivation of blood pH

Answer 7

(pic)

pic

Question 8

Definitions-
acidemia
alkalemia
acidosis
alkalosis

Answer 8

Acidemia: a decrease in blood pH below 7.4
Alkalemia: an increase in blood pH above 7.4
Acidosis: the physiological process responsible for the acidemia
Alkalosis: the physiological process responsible for the alkalemia

Question 9

“The Goldilocks Zone”

Answer 9

With every 10-fold decrease in [H+] the pH increases by 1 unit.

acidemia
pH 7.2
H+ (mols/L)- 6.3 x 10^-8
change in acidity +58%

normal
pH 7.4
H+ (mols/L)- 4.0 x 10^-8

alkalemia
pH 7.6
H+ (mols/L) 2.5 x 10^-8
change in acidity -38%