Acid-base Theory, pH, pKa & pKb- go over it as coculations are needed Flashcards
Weak Organic Acids
Aspirin, Ibuprofen, Diclofenac, Benzylpenicillin
Weak Organic Bases
Morphine, procaine, Benzocaine, Chloramphenicol
their salt
Ephedrine hydrochloride, sodium ibuprofen, potassium diclofenac
A Lowry-Brønsted ACID
is a proton DONOR
strong acid full ionisation
weak acids partial ionisation
A Lowry-Brønsted BASE
is a proton ACCEPTOR
ampholyte
act as an acid or base
is called an AMPHOLYTE
and is said to be AMPHOTERIC in nature.
Acid1 /Base1 and Acid2/Base2 in such an equilibrium are
known as Lowry-Brønsted conjugate acid-base pairs
The Dissociation of Weak Acids
The dissociation of a WEAK ACID in aqueous conditions can be represented as follows: HA + H2O A- + H3O+
The equilibrium constant (for a weak acid) may be expressed as follows:
[H3O+][A-] Ka = ---------------- [HA] pKa = - log Ka
The lower the pKa-the stronger the acid
The Dissociation of Weak Bases
The dissociation of a WEAK BASE in aqueous conditions can be represented as follows: B + H2O OH- + BH+
The equilibrium constant (for a weak base) may be expressed as follows:
[OH-] [BH+] Kb = -------------
[B]
pKb = - log Kb
The lower the pKb-the stronger the base
The pKa and pKb values of a conjugate acid-base pair are linked by the following expression
pKa + pKb = pKw
Where pKw is the negative log of the dissociation constant for water (Kw).
At 25oC : pKw = 14.00
Amphoteric electrolytes
are electrolytes which can function as either acids or bases ( amino acids and proteins).
Example: Over the pH range 3-9, glycine exists in solution predominantly in the form +NH3CH2COO-.
Such a structure, having both positive and negative charges on the same molecule, is referred to as “ZWITTERION”:
acidic conditions becomes main base
basic conditions main molecule becomes acidic
capable of donating or accepting more than one proton are
polyprotic
pH-Dissociation profiles for weak acids and bases
pKa = pH at which 50 % of species are ionised.
At 2 pH units away from pKa weak electrolytes are completely dissociated/undissociated
The acidic drug is completely unionised at PHs up to 2 units below its PKA and virtually completely ionised at PH greater than 2 units above its Pka
The Conjugated Base of a Strong Acid
is a weak
The Conjugated Acid of a Strong Base
is a Weak Acid
Electrolyte
is a compound that is ionised in solution.
Electrolytes yield ions when dissolved in water and therefore could conduct an electric current through solution.
Non-electrolytes
are substances that do not yield ions when dissolved in water and therefore do not conduct an electric current through the solution.
Examples of non-electrolytes are:
- Sucrose
- Glycerin
- Naphtalene
- Urea
- Steroids
weak acid + strong base
will make a salt and the addition of water will make salt and oh-
Buffers
Resistant to changes in pH.
Usually a mixture of a weak acid and its salt (conjugate base), or of a weak base and its salt (conjugate acid).
common ion effect
is a decrease in the solubility of an ionic compound as a result of the addition of a common ion
addition of an equal
concentration of a salt with a common ion
Buffer Capacity -
Also known as “buffer efficiency”, “buffer index” and “buffer value
is defined as the ratio of the increment of strong base (or acid) to the small change in pH brought about by this addition.
HH EQN- weak acids
HH EQN- weak base
HH EQN buffer equation for weak base
HH EQN buffer equation for weak acid
