Acid Base Theory and Henderson Hasselbach Equation Flashcards
(26 cards)
Why is acid-base theory relevant to pharmacology and drug design?
Most drugs are weak acids or bases and as such experience acid-base interactions which must be considered.
What is the Bronsted-Lowry acid-base model?
The model in which acids and bases react to form their conjugate opposites (acids react to form conjugate bases).
What is an amphiprotic solvent?
A solvent which can act as either an acid or a base.
What is an ampholyte?
An electrolyte that can act as either an acid or a base.
What is an electrolyte?
A substance which dissociates to release ions.
What does it mean if a substance is polyprotic?
It can release or accept more than one proton.
Does a polyprotic substance have one pKa or multiple? Why?
Multiple. Once it has already released or accepted a proton its chemistry changes and is therefore modelled by a new constant.
What does a low pKa tell you about a substance?
It is acidic.
What does a high pKa value tell you about a substance?
It is basic.
State the Henderson Hasselbach equation for weak acid dissociation:
pH = pKa + log([A-]/[HA])
What is the main use of the Henderson Hasselbach equation?
To illustrate the effect of pH on the degree of drug ionisation
State the Henderson Hasselbach equation for weak base dissociation:
pH = pKa + log([B]/[BH+])
What is the % ionisation equation?
% ionised = (10^pH-pKa)/((10^pH-pKa)+1)
Why do strong acids/bases fully donate/accept protons?
Because their reactions are virtually irreversible.
What makes an acid/base weak?
It only partially dissociates in solution, releasing/accepting much fewer protons than a strong equivalent.
Define a strong electrolyte:
A compound that completely ionises in aqueous solution.
Define a weak electrolyte:
A compound that only partially ionises in aqueous solution.
What is the association between electrolytes and acids/bases?
All acids and bases are electrolytes (as they ionise in aqueous) but not all electrolytes are acids/bases since they don’t necessarily release or accept protons.
How is a buffer often made? Why can’t a strong acid/base be used to make a buffer?
Combination of a weak acid/base and their conjugate salt.
Since they dissociate fully, strong acids/bases do not have a reservoir of non-dissociated acid/base necessary for buffer action.
What is the function of a buffer?
To resist small(ish) fluctuations to changes in pH.
Why are acidic buffers preferred to basic buffers?
Acidic buffers are less prone to being affected by temperature changes and remain more functional.
Why are acetate buffers so commonly used?
They remain functional as pKw changes and can be used at a variety of temperatures.
What is the common ion in a buffer equation?
The ion shared by the dissociation of a weak acid/base and its conjugate salt.
Define buffer capacity:
The magnitude of the resistance of a buffer to pH changes.
