Lecture 3: Acids, Bases, And Buffers Flashcards
Most chemical reactions are ___
Reversible
What does dynamic equilibrium mean?
- Reactants can combine to give products
- Products can fall apart to give reactants
What does Le Chatelier’s Principle state about equilibrium?
When a system in a state of dynamic equilibrium is disturbed, it will react to re-establish the equilibrium condition; nature likes being in an equilibrium state
A system is in a state of equilibrium when there is a…
balance between reactants and products
As K increases, the reaction tends to increasingly favor…
Products
As K decreases, the reaction tends to increasingly favor…
Starting materials (the reverse reaction becomes more favorable)
K subscript a =
Weak acids
If you add products, the equilibrium will shift towards…
reactants
If you remove products, the equilibrium will shift toward…
products
What is Bronstead acids and bases?
The most generally useful definition of an acid
An acid is a ___
proton (hydrogen ion) donor
A base is a ___
proton (hydrogen ion) acceptor
Proton donor =
Acid
Proton acceptor =
Base
When an acid donates a proton, it is converted into its ___ ___
Conjugate base
When a base accepts a proton, it is converted into its ___ ___
conjugate acid
What is an amphoteric species (amphiprotic species)? Give an example.
Something that can behave as either an acid or a base, i.e.: water
The stronger the acid, the weaker the ___ ___
conjugate base
The weaker the acid, the stronger the ___ ___
conjugate base
Weak acids do not…
Ionize 100% in water
Weak bases establish an equilibrium by…
Accepting a proton from water
The pH scale quantitatively describes…
The “acidity” or “alkalinity” of a solution
PH 7
Neutral
PH < 7
Acidic
PH > 7
Basic
A system is in balance (equilibrium) when there is a balance between…
the reactants and products
What is K?
K is the equilibrium constant which provides a numerical description of that balance
As K increases, the reaction tends to increasingly favor ___
products
As K decreases, the reaction tends to favor ___
The starting materials
PKa is the point at which…
50% of a drug is ionized, and 50% of the drug is nonionized
A pH buffer is…
a solution that resists changes in pH
A pH buffer may contain…
a weak acid (HA) in its conjugate base
When the concentration of a weak-acid and its conjugate base are equal, the ___ is equal to the ___
pH is equal to the pKa
When is the pH equal to the pKa?
When the concentration of a weak-acid and its conjugate base are equal
Drug utilization by the body is determined by…
the degree of ionization/non ionization
Non ionized drug is…
lipid soluble and readily penetrates the blood brain and placental barriers
Lipid soluble =
non water soluble = hydrophobic
The ionized form of a drug is…
water soluble (hydrophilic)
What determines drug effectiveness?
Knowing the degree of ionization or non ionization
What are 3 steps to determine ionization?
- Is the drug a weak acid or a weak base?
- What is the pKa of the drug? (This is your reference point)
- What is the pH of the target solution that the drug is being placed in? (Usually the body where the pH is 7.4).
Weak acids become more ___ as pH falls (H+ increases)
more nonionized
acid + acid = nonionized
Weak acids unite with ___ charged ions such as…
positively charged
I.e.: Na+, Mg++, Ca++
So, if you see a salt drug (i.e.: sodium drug, calcium drug, magnesium drug), you would recognize the drug as…
the salt base form of a weak acid (i.e.: sodium pentobarbital is a salt of a weak acid)
Weak bases become more ___ as pH increases (H+ decreases)
more nonionized
Base + base = nonionized
Weak bases unite with ___ charged ions
Negatively
If you see salts: i.e.: “drug” chloride, “drug” sulfate, recognize them as…
the salt form of a weak base (i.e.: Lidocaine hydrochloride and morphine sulfate are salts of weak bases)
Sodium drug, calcium drug, magnesium drug =
Salt form of weak acids
“drug” chloride, “drug” sulfate =
Salt form of weak bases
What is the pKa of a weak acid or weak base?
The pKa of a weak acid or weak base is the pH at which 50% is ionized and 50% is nonionized
The nonionized form of a weak acid =
the acid
The ionized form of a weak acid =
Conjugate base
The nonionized form of a weak base =
The base
The ionized form of a weak base =
Conjugate acid
The nonionized drug of weak acids penetrates…
the blood brain barrier and placental barrier
The greater the nonionized portion of the drug, the greater the transfer to…
brain and fetus (ion trapping in fetus)
What are 3 examples of weak acid drugs?
- Thiopental
- Barbiturates
- PROPOFOL***
What are 3 examples of weak base drugs?
- Lidocaine (locals)
- Morphine (opioids)
- Versed (benzos)
What happens to local anesthetics in fetal circulation?
-Trapping of local anesthetics in fetal circulation
Why does ion trapping occur in fetal circulation?
The pH of the fetus is lower than maternal, so the circulating nonionized drug crosses the placental barrier
