pH and buffering Flashcards
What is pH?
-A measure of hydrogen ion concentration (acidity or alkalinity of a solution)
What does acidity depend on?
-Acidity depends only on free hydrogen ions
-Not those still bound to anions
What is the normal range of pH in the body?
7.0 - 7.8
7.4 is healthy
What regulates acid base balance?
-Lungs
-Kidneys
-Chemical buffers
How do buffers maintain pH of body fluids?
-Release H+ when pH begins to rise
-Binds H+ when pH drops
When H+ = 10^-2 M, what is the pH?
pH 2
When H+ is 10^-2, what is OH-?
10^-12
log reminder
How many more H+ ions are there for 7.4 to 7.3
- 10 times as many
Difference between acids and bases
-Acids are proton (H+) donors
-Bases are proton (H+) acceptors
Difference between strong acids and weak acids
-Strong acids dissociate completely in solution
-Weak acids dissociate incompletely in solution (can dissociate completely at the right pH)
What is the pKa?
-The pH at which you have equal amounts of dissociated and non-dissociated forms of acid (conjugate base and acid)
-Lower the pKa, stronger the acid
-At pKa buffering is best
How do you know if solution is buffering?
Flat graph = buffering
Line shoots up = Not buffering
Triple dissociation of phosphoric acid
What are buffers?
-Buffers are mixtures of weak acids and their conjugate bases
-Buffering is the ability of a solution to resist a change in pH when acid or alkali is added
What are some physiological buffers?
-Bicarbonate
-Phosphate
-Plasma proteins
How can plasma proteins be used as physiological buffers?
-Proteins lose hydrogen to form negatively charged protein
-Positively charged proteins can lose hydrogen to form neutral proteins
What makes haemoglobin a good blood buffer?
-The presence of a large number of histidine residues
If pH of blood is 7.4, is oxyhaemoglobin (pKa 6.8) or deoxyhaemoglobin (pKa 7.8) better able to pick up and carry H+ ions?
Deoxyhaemoglobin (pKa 7.8) carries more H+ ions than oxyhaemoglobin (pKa 6.8) at blood pH of 7.4
Aspirin has a pKa of around 3. At which pH would it cross a membrane more easily? pH 8 or pH 2?
pH 2
-At a pH above the pKa, an acid will dissociate and become charged
-Therefore, at pH 8 aspirin would dissociate and become charged, at pH 2 it would not
-Uncharged molecules pass more easily through membranes
If pH is above/below pKa of an acid, how will it affect its dissociation?
-At a pH below the pKa, an acid will remain undissociated
-At a pH above the pKa, an acid will dissociate and become charged
-It will carry more H+ ions
