pH & Buffering
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What is pH?
A measure of hydrogen ion concentration
What hydrogen ions does acidity not depend on?
Hydrogen ions not bound to anions
What is the normal pH range of blood?
7.35-7.45
Where does acid in the stomach come from?
Some acid enter in food. Breakdown of proteins, incomplete oxidation of fats or glucose. Loading and transport of carbon dioxide in blood.
What is the acid - base balance regulated by?
The lungs, kidney, systems in the blood called chemical buffers
What do buffers do when the pH rises or falls?
rise - released H+ fall - binding H+
What molar solution is pure water?
55.6M solution
What magnitude must the concentration of hydrogen ions and hydroxide ions equal?
10 to the -14
How is pKa shown on an acid dissociation curve?
The straight line where buffering is occuring
Where can a good blood buffer, buffer at?
pH 7
What is a definition for Ka?
The pH at which the acid is half dissociated. There are equal amounts of undissociated acid and its conjugate base.
The lower the pKa, the —- the acid?
Stronger
What is the Henderson Hasselbalch equation?
pH = pKa + log (acid / conjugate base)
How does pKa relate to buffering?
• Buffers are mixtures of acids and their conjugate bases • Buffering is the ability of a solution to resist a change in pH when acid/alkali is added • At the pKa, there are equal amounts of dissociated and non dissociated forms of the acid • At the pKa, buffering is best
At what pH does the alpha carboxyl and alpha amine group deprotonate?
carboxyl = pH 2 amine = pH 10
Which amino acids are the ones with can dissociate?
Electrically charged ones
What makes haemoglobin a good buffer?
The large number of histidine residues. When oxygen is delivered, the pKa value increases
What is critical pH?
Highest pH at which there is a net loss of mineral from the teeth
Why is the critical pH not an exact value?
The solubilty of enamel apatite varies with pH and teeth are buried in constantly replenished saliva which the concentration of calcium and phosphate ions varies.
How could we get a tooth to withstand a lower pH before demineralising?
Increasing local concentrations of calcium and or phosphate
What are all local anaesthetic agents? What two forms can the exist in?
Weak bases, unionised and ionised