Ch. 3-Ionization of Drugs Flashcards
What does the pH scale measure, and what numbers on the scale correspond?
it measures how acidic or basic a substance is -scale from 0 to 14 7=neutral 0-6=acidic 8-14=basic
What does pH stand for?
power of hydrogen
How are the concentration of hydrogen ions and pH related?
- the higher the concentration of H ions, the lower the pH (acidic)
- the lower the concentration of H ions, the higher the pH (basic)
If one solution has a pH of 6 and another solution has a pH of 5, which one has more H ions?
solution with pH of 5 has more H ions and is therefore more acidic
1 degree difference in pH equals how much of a difference in H ion concentration?
10x difference
-ex) solutions with pH’s of 5 and 6 have 10x difference, with pH of 5 and 7 have 100x difference
acid
“donor”
it donates H ions to a base
base
“recipient”
it receives H ions from the acid
What is the normal pH of human blood, and what happens if it were to change?
7.35-7.45 (slightly basic)
if the pH changes the drug would become ionized, and it is impossible for ionized drug to cross cell membrane
buffers
“shock absorbers”
prevent pH changes in the body when H ions are added or removed
-extracellular buffers and intracellular buffers
major and minor extracellular buffer
- HCO3- (bicarbonate, major)
2. phosphate (urinary buffer, minor)
major and minor intracellular buffers
- hemoglobin (major)
- organic phosphate
- proteins
How do buffers work?
acid lowers the pH, so it would react with the base bicarbonate (HCO3-) to turn the acid into a weak acid
-base reacts with carbonic acid (H2CO3) to turn the base into a weak base
What two buffers are a pair and are always present in the system?
bicarbonate (HCO3-) and carbonic acid (H2CO3)
bicarbonate
HCO3-
reacts with acids to make them weaker
carbonic acid
H2CO3
reacts with bases to make it a weak base
weak acid
partially dissociates in water
thiopental and barbiturates
-more nonionized when H increases (lower pH)
-more ionized when H decreases (higher pH)
——-charge goes up and down with pH level
weak base
local anesthetics
partially dissociate in water
-more nonionized when H decreases (higher pH)
-more ionized when H increases (lower pH)
——charge goes up or down with H concentration
titration curve
describes how pH changes when H is added or removed
- H added=HA form, lowers pH, more acidic
- H removed=A- form, raises pH, more basic
pK of a solution
when both sides of reaction are in equilibrium-there are equal numbers of ionized and nonionized ions
-also located at center of titration curve
strong acids
completely dissolve in water
common acids-H2SO4 (sulfuric acid), HCl (hydrochloric acid), and HNO3 (nitric acid)
strong bases
completely dissociate in water
NaOH (sodium hydroxide), KOH (potassium hydroxide), and Ca(OH)2 (calcium hydroxide)
law of mass action
characterizes chemical equilibrium
