IONIC EQUILIBRIUM & BUFFERS Flashcards
formation of ions
ionization
separation of a species into to two or more
dissociation
The equilibrium established between the unionized molecules and the ions in the solution of weak electrolytes.
ionic equilibrium
degree of ionization is pH dependent
weak electrolytes
particles have no charge
unionized
with charge
ionized
Acid + acid
unionized, lipophilic, insoluble
Base + base
unionized, lipophilic, insoluble
Acid + base
salt form, ionized, hydrophilic, soluble
Formed by a chemical reaction between: a base and an acid.
salts
will not completely dissolved in water; they only partially dissolved in water
weak acid & base
Protolysis or the transfer of protons
Protolytic Reaction
A basic solvent capable of accepting protons from the solute
e.g., acetone, ether, liquid ammonia
protophilic
A proton-donating compound and is represented by acids
formic acid, acetic acid, sulfuric acid, liquid HCl, and liquid HF
protogenic
Neither accept nor donates protons
hydrocarbons
aprotic
A specie that can function either as an acid or base and are said to be amphoteric in nature
ampholyte
Compounds or mixtures of compounds that by their presence in a solution, resist changes in pH upon the addition of small quantities of acid or alkali
buffers
acetic acid and sodium acetate
weak acid & conj base
ammonium hydroxide and ammonium chloride
weak base & conj acid
resistance to a change in pH
buffer action
acidity constant
Ka
basicity constant
Kb
self-ionization of water
Autoprotolysis
acts both as an acid and as a base
amphoteric
water dissociation constant
Kw
donates/accepts one proton (one Ka)
monoprotic
donates/accepts two or more protons
polyprotic
The degree of acidity and basicity depends on
H+, OH-, pH or pOH
pH value
negative logarithm of a value
p function
pH and pOH lie between
0 - 14
The ____ in the scientific notation gives you an idea of the pH, and vice versa.
exponential term
pH = 8
[H+] = 1 x 10-⁸
the higher the OH-, the more ____ the substance is
basic
the higher the H+, the more ____ the substance is
acidic
strong acid
pH = -logCa
strong base
pH = 14 + logCb
weak acid
pH = -1/2log(Ca x Ka)
weak base
pH = 14 + 1/2log(Cb x Kb)
The magnitude of resistance of buffer to pH changes
Buffer Capacity (β)
Buffer Capacity (β) is also known as
Buffer index
Buffer efficiency
Buffer value
Exact Equation for Buffer Capacity
B = 2.3C (Ka[H+] / (Ka + [H+])²
C = total conc. of buffer
Maximum Buffer Capacity
0.576C
BLOOD
maintained at pH ____
7.4
primary buffer in plasma
BLOOD
BLOOD
secondary buffer in
erythrocytes
BLOOD
life threatening at pH
less than 6.9, greater than 7.8
LACRIMAL FLUID (TEARS)
maintained at pH
7.4
LACRIMAL FLUID (TEARS)
discomfort & flow of tears at pH
less than 6.6, greater than 9
average pH of urine
6 (about 4.5 - 7.8)
Frequently used in formulation of ophthalmic solutions
pharmaceutical buffers
Boric acid + sodium carbonate (pH 5-9)
GIFFORD
Salts of sodium phosphate + NaCl (pH 6-8)
SORENSEN
Salts of sodium phosphate + NaCl (pH 6-8) is also called
PHOSPHATE BUFFERED SALINE (PBS)
Boric acid + sodium borate + NaCl (pH 7-9)
PALITZSCH
CLARK-LUBS MIXTURES
HCl & KCl
1.2 - 2.2
CLARK-LUBS MIXTURES
HCl & potassium hydrogen phthalate
2.2 - 4.0
CLARK-LUBS MIXTURES
NaOH & potassium hydrogen phthalate
4.2 - 5.8
CLARK-LUBS MIXTURES
NaOH & KH₂PO₄
5.8 - 8.0
CLARK-LUBS MIXTURES
H₃BO₃, NaOH, & KCl
8 - 10
General Procedures for Preparing Pharmaceutical Buffer Solutions
Select a weak acid having pKa approximately ____ to the desired pH at which the buffer is used
equal
General Procedures for Preparing Pharmaceutical Buffer Solutions
Calculate the ____ of salt and weak acid.
molar ratio
General Procedures for Preparing Pharmaceutical Buffer Solutions
Concentration of individual salt and acid of ____ is sufficient
0.05 - 0.5M
General Procedures for Preparing Pharmaceutical Buffer Solutions
Determine the ____ and ____ Adjust if necessary.
pH & β
Expressing the quantities of the hydroxide and hydrogen ions into a logarithmic scale
SORENSEN’S pH
- One of the most important properties of a drug
- Can be related to
o Physiologic and pharmacologic activity
o Solubility
o Absorption - Predicts which direction an acid-base reaction lies and what extent the reaction goes to completion
o Measures the extent on how a weak acid or weak
base will undergo ionization or not
Acid dissociation constant
Acidity constant
Ka