Significance of pH Flashcards
What do buffers do?
Maintain pH of body within normal pH ranges
What is the normal pH range for blood?
Around 7.4
What is the normal pH range for urine?
Around 6.0 (range 4.4 - 8.0)
What is the normal pH range for gastric fluid?
Around 2.0
What is the normal pH range for saliva?
Around 6.2 - 7.2
What are 2 inorganic buffers found in the body?
Phosphate and bicarbonate
What is the equation for the pH scale?
pH = -log10[H+]
What does the dissociation of acids release?
Hydrogen
What is an acid?
A substance which in water tends to produce H+ ions
What is a base?
A substance which in water tends to combine with H+ ions
What do you ned for the dissociation of an acid?
The forward reaction must be balanced by the reverse reaction
What is the acid dissociation constant (Ka) equation?
Ka = [H+][B-]/[A]
What is the Ka of a strong acid?
Ka is greater and so the reaction is pushed to the right
What is the Henderson-Hasselbalch Equation?
pH = pKa + log10[B-]/[A]
where pKa = -log10Ka
What is the Ka and pKa of a stronger acid?
Larger Ka and therefore smaller pKa
What is an indicator?
Weak acids or bases which in the ionised form and unionised form show a difference in colour
What is the dissociation equation of an indicator?
pH = pKa + log10[In-]/[HIn]
Why is very little indicator added to a reaction?
So that the pH of the solution is unaffected
Why is an electrical method (e.g. a pH meter) a better way of measuring pH?
They are more accurate
What do buffer solutions do?
Resist changes in pH when acids or bases are added
What do buffer solutions consist of?
A conjugate acid-base pair of either a weak acid or a weak base
Why are buffering systems in the body important?
They maintain pH homeostasis
What do buffering systems in the mouth do?
Limit pH changes due to acid production by plaque bacteria
When do buffers operate optimally? (when are they most effective?)
At their pKa e.g. when they are HALF DISSOCIATED
