pH, buffers, acid dissociation
Treatment
How a doctor might treat the pH imbalance E.g in case of hyperventilation- calming patient (decreasing breathing rate) or make patient breathe into paper bag (decreasing loss of CO2)
Compensation
How the body responds to the pH imbalance. e.g excreting more HCO3- to compensate for pH increase caused by an increased breathing rate (e.g in hyperventilation)
Effect of increased ventilation
Increased BR expels surplus CO2 from the body, eqm shifts to right (decreases H+)
How may a gain in acid occur (3)
Ingestion of acid Increased retention of acid by kidneys Increased production of acid.
How may gain in alkali occur
Ingestion of alkali
Why is it a base
It can accept protons and act as a base.
What happens when all the acid has been deprotonated
It can no longer counteract addition of alkali, so any addition will sharply increase the pH.
Kidneys/ lungs comparison of the bicarbonate buffer system
Kidneys can slowly affect H+ & HCO3- but the lungs can respond more rapidly to change in pH by expelling or retaining CO2
Bicarbonate buffer system equation
Look in notes
Metabolic alkalosis
Loss in acid Gain in alkali Gain in HCO3-
How can the pH of the buffer be controlled?
pKa is a constant for every buffer so pH is controlled by altering the rel concs of the weak acid and its conjugate base.
Causes of acidosis and alkalosis (2 groups)
respiratory metabolic.
What is K
the equilibrium constant
What is the pKa value
the pH where [A-] / [HA] = 1
Mechanism by which buffers work
the weak acid and its base exist in an equilibrium. Adding acid drives the reaction backwards and adding base drives the reaction forwards. Effectively, buffers resist changes in pH by replacing lost protons or mopping up extra ones.
Loss of HCO3- results in...
(base) so it drives the equilibrium backwards, resulting in an increase in H+ and decrease in pH.
pH equation
- log [H+]
pK equation
- log [K]
If you have an acid, and you add alkali, what are the changes in protonation that occur. TITRATION PROCESS.
1) Acid begins with all of it being in the *protonated* form 2) As you add alkali and there is a decrease in H + conc, *dissociation* of acid occurs to replace lost H+ ions. This is known as *deprotonation* 3) When half the acid has dissociated/ deprotonated, pH= pKa 4) Above pKa, the acid will be mostly *deprotonated* as > 1/2 will have dissociated in response to the alkali
2 ways of making a buffer
1) dissolving the acid with its corresponding salt 2) adding a strong base/ acid to the weak acid/ conjugate base.
When do amino acids lose protons from its acidic and basic groups
From acidic groups at low pH From basic groups at higher pH
Metabolic acidosis
Gain in acid Loss in alkali Loss in HCO3-
H+ conc
10 ^ -pH
How many pKa's do amino acids have
2 (sometimes 3)
Blood pH is kept within
7.35 and 7.45
What is a buffer
A solution that resists changes in pH when small amounts of acid/ alkali are added.
Respiratory acidosis/ alkalosis
Acidosis - retention of CO2 Alkalosis - loss of CO2
Buffer pH range?
All buffers have a pH range over which they are most effective and the midpoint of this range is the pKa of the buffer.
Why is regulation of pH in body fluids essential?
Bc many proteins, e.g ion channels, enzymes are sensitive to changes in pH.
How is pH maintained within the body.
Both intracellular & extracellular fluids contain buffers (e.g phosphate and proteins) which can accept protons when pH is too low or release when pH is too high.
How do you determine the strength of an acid?
By the pH at which it completely dissociates. Strong acids can completely dissociate even in acid conditions but weak acids require higher pH (more alkaline solution) before they completely dissociate.
What experiments are buffers commonly used in
Enzyme experiments.
Why are buffers useful in enzyme experiments
Enzymes function best at certain narrow pH ranges so their activity can only be measured at these pHs. Buffers can keep the pH at the enzymes optimum pH
Is the pH of intracellular fluids the same in each cell type?
No. pH of intracellular fluids varies between cell types but is affected by the pH of the extracellular fluid.
What do we mean by the fact that the body's responses to pH changes are indirect?
Respiratory mechanisms compensate for metabolic causes and vice versa
Effect of decreased ventilation
Retains more CO2, eqm pushed to left, increasing H+
Strong acid / weak acid definition
Strong acid- completely dissociates in solution Weak acid - partially dissociates in solution.
What are oxonium ions
When hydrogen ions are attached to water molecules (H3O +)
Effect of administering acid.
Will react with extra HCO3- and directly decrease the pH.
What does a buffer contain
a weak acid in solution with its conjugate base
Metabolic response to acidosis & alkalosis
acidosis- administer HCO3- alkalosis - administer acid.
Respiratory response to acidosis and alkalosis
acidosis- increased ventilation alkalosis- reduced ventilation
Why would an amino acid have 2 pKa's
bc it has 2 groups that can act as proton donors/ acceptors. hence 2 pKas
Why might some amino acids have a 3rd pKa
because the R groups of some are either acidic or basic.
Alkalosis
blood pH too high
Acidosis
blood pH too low.
What would you see in a compensated acid-base disorder
both [HCO3-] & [CO2] will be abnormal, but pH will be near the normal pH range for healthy patient
When might larger changes in pH occur
buffers have a pH range over which they act. outside this range, the addition of strong acids/ bases will result in larger pH changes.
How can the pH of the blood be regulated
by maintaining a particular HCO3 - and CO2 ratio
What is A-
conjugate base- deprotonated form of the acid
Loss of acid results in...
directly results in increased pH
Retention of CO2 results in...
equilibrium shifted backwards, increased H+ leads to decrease in PH.
Loss of CO2 results in
equilibrium shifted forwards, decrease in H+, so increase in pH
Gain of alkali results in...
excess alkali reacts with H+, decreasing its conc so increase in pH
Loss of alkali results in...
increase in conc of H+ so lower pH
What does the Henderson Hasselbach equation show
it relates the pKa of the buffer and the relative concs of the acid and its conjugate base to the actual pH of the solution.
Gain of acid results in
more H+, decrease in pH, equilibrium shifts forwards, results in more CO2 production
Gain in HCO3- results in...
more reacts with H+, decreasing its conc so increase in pH.
Effect of administering HCO3-
more will react with H+, shifting eqm to right, away from production of H+
