Acids and Bases Flashcards
What is an acid?
A molecule or ion which tends to give up protons in solution (PROTON DONOR)
What is a base?
A molecule or ion which tends to acquire protons in solution (PROTON ACCEPTOR)
What does an acid dissociate into?
Hydrogen ions and the conjugate base
What is the formula for the rate of the forward and reverse reaction?
V1 = K1[HX] V2 = K2[H].[X]
What is the Ka?
An acid dissociation constant - quantitative measure of strength of acid in solution
Products/reagents so
Ka = k1/k2 = [H].[X]/[HX]
Larger Ka the more reaction favours the product and the stronger the acid/base
Smaller the pKa, the stronger the acid.
pKa = -log(Ka)
What are three important acids in biology?
Carbonic acid - formed when CO2 dissolves in blood tissue fluids, acts as a buffer at physiological pH due to bicarbonate ion
Lactic acid - formed by human cells from glucose during anaerobic respiration, especially in muscle during rapid movement, causes cramp
Is converted to glucose via gluconeogenesis in the liver (cori cycle)
Hydrochloric acid - secreted into the stomach as part of digestive process
How do acids cause destruction of calcium phosphate (hydroxyapatite)?
Increase in [H] causes equilibrium to shift to right, increasing solubilisation of calcium phosphate - hence why acidic food/drink is bad
Increase in calcium/phosphate concentration causes equilibrium shift to left, inhibiting solubilisation and promoting remineralisation
Saliva contains calcium and phosphate
Other than low pH how do fruit juices cause tooth erosion?
They contain organic acids (e.g. citric) which act as chelating agents, these bind to calcium ions which are then no longer available to couneract calcium solubilisation.
What is a buffer?
An aqueous solution containing a weak acid and its conjugate base, or a weak base and its conjugate acid.
pH changes very little when small amount of strong acid or base added - used to prevent any change in pH of a solution
What pH are acid/conjugate base pairs good buffers and how can they be made?
At the pH whereby there is 50% acid and 50% base (because they can equally mop up as much H as OH ions)
They can be made by either neutralizing an acid with OH or mixing together a solution of acid and one of its salts with the appropriate Ka
What is the henderson-hasselbach equation?
pH = pKa + log([H].[X])/[HX])
What are the buffering components of saliva?
Bicarbonate ion - main buffer
Phosphate and histatins
Where does bicarbonate in saliva come from?
Partly from the blood
Partly from the action of carbonic anhydrase - enzyme in salivary gland
Carbonic anhydrase dissociates into bicarbonate and hydrogen ions
What are the three different pH ranges that phosphate acts as a buffer?
- phosphoric acid, pKa =2
- Dihydrogen phosphate pKa = 7
- Monohydrogen phosphate pka = 12
On a graph of pH of solution against volume of solute added where is the region where the buffer is best?
Mid-point of a flat region
