2.5 Acids & Bases Flashcards
What was the earlier definition of an acid?
Arrhenius
Acids release H+ when dissolved in water
Base releases OH- when dissolved in water
What are the Bronsted-Lowry definitions of acids and bases?
Acid = H+ donor
Base = H+ acceptor
How does Lewis describe acids and bases?
Acids = electron pair acceptor
Base = electron pair donor
What are the opinions on neutrality by the 3 acid base theories?
Arrhenius - Acids and bases can neutralise one another
Bronsted-Lowry & Lewis- Acids and bases can not reach neutrality
3 Strong acid examples
HCl
H2SO4
HNO3
What do strong acids do in solution?
Completely dissociate
Organic acid and bases are usually….
Weaker
Only partially dissociate in solution and form an equilibrium
What is the concentration of H+ or OH- ions released in strong acids and bases?
Same as concentration of starting acid or base
Acid + base =
Salt (+water)
In strong acids and bases, the base’s OH- is protonated by the H+ of the acid to produce water
When is water not produced in acid + base reactions?
When there’s weak acids or bases.
If base doesn’t contain a hydroxide, it can form a salt by accepting a proton. So water is not produced.
If base contains a carbonate or hydrogen carbonate, then CO2 is released.
What is a salt defined as?
The product of when you replace the proton component of an acid
What is the difference between Bronsted-Lowry and Lewis?
Bronsted-Lowry describes the accepting or donating of a proton.
Lewis describes accepting or donating electron pairs
Get head around previous slide
What are conjugate acids and bases?
Species that act as acids or bases in the reverse direction of reaction
What are conjugate pairs?
Species that are related but act as opposites (one as acid and other as base) on either side of the reaction
Learn Ka and Kb Equations
See pic
What is pH a measure of?
Concentration of H+
pH =
pH = -log10 [H+]
eg. 1 × 10^-6 M = pH 6
pOH =
pOH = - log10[OH-]
Low pH =
Stronger acids
Ka and [H3O+] increase
Higher pH =
Stronger bases
Kb and pH increase
pKw =
pKw = pH + pOH = 14
REMEMBER
What is an indicator?
A weak acid molecule that changes colour with the change of equilibrium position
The indicator’s energy levels change significantly when it’s protinated 2hich changes its colour
[H+] produced from a strong acid =
Starting concentration of the strong acid
In monoprotic acids
Who do u work out pH of a weak acid?
By working out the Ka
What is the 1st assumption used when calculating pH of a WEAK acid?
The only thing producing H+ is the dissociation of acid
This means H+ = A-
What is the 2nd assumption used when calculating pH of a WEAK acid?
The acid dissociation is really small so…
The starting concentration = equilibrium concentration
The amine group of an amino acid is…
A weak base
The carboxylic group of an amino acid is….
A weak acid
What does the degree of dissociation in an amino acid depend on?
The pH of the solution relative to their Ka
When pH < pKa
It’s more acid
Functional group more protonated than unprotonated
When pH = pKa
Functional group is 50/50
Protonated = unprotonated
When pH > pKa
The functional group is more deprotonated
Knowing if a molecule is ionised at a particular pH, allows a pharmacologist to predict…
How easily something is absorbed
And how soluble it is
(These are important properties for understanding the behaviour of a drug)
Learn graph shapes
See pic
What do buffers rely on? And what do they do?
They rely on le chateliers principle to maintain pH of a system against external change.
This change can be addition of acids of bases
What are buffers formed from
Weak acids or weak bases
What does the buffer capacity of a solution depend on?
How much of the acid and how much of the conjugate base (HA and A-) you have present
What are buffers used for in labs?
To hold experiments at certain pH
How is the pH of a buffer calculated?
Using the Henderson Hasselbalch equation
pH = pKa + log ([A-]/[HA])
Where is bicarbonate used as a buffer?
Lungs and kidney
It buffers acids produced by metabolism and respiration
What is looked for in blood tests to check for Acidosis OR Akolosis?
pH of blood & Concentration of anions in the body’s buffer system
What is the Haemoglobin buffer system in blood important for?
Carbon dioxide
What acts as buffer in intracellular fluid?
Amino acids of proteins can be protonated or unprotonated as a result of change in pH
And phosphates
What is used as buffers in the kidney?
Ammonia
Ammonium
Phosphates
Longer response period
What buffer systems are present in bones?
Inorganic components of skeleton are basic. A prolonged acidosis, will cause leaching of calcium and phosphates from skeleton
What maintains pH in the blood?
Bicarbonate in blood plasma
Rapidly responding- dependant on amount of CO2 breathed out
What is the product of CO2 dissolving in water?
Carbonic acid, H2CO2
What can change the blood’s pH?
Restricted exchange of CO2
What happens when too much CO2 is breathed out (hyperventilation) due to panicking?
H2CO3 is lost
Blood becomes slightly Alkaline
Can pass out as respiratory drive resets
What happens when breathing is restricted?
Too much CO2
Too much carbonic acid
Too high a pH
Metabolic acidosis happens from?
Build up of other Acidic waste products
What can u get oalic acid from?
Poisoning
Ingestion
Metabolism of ethelene glycol
Diabetic keto acidosis signs
Very slow very deep breathing - to exchange more CO2
What parts of proteins can be protonated?
Haemoglobin and intracellular proteins (Histidine)
Which amine can be protonated?
Lysine
It can form reversible bond with CO2 - this changes affinity of haemoglobin to transport O2
