Acids and Bases Flashcards
What is the oxonium ion?
H3O+
What is an Arrhenius acid?
An acid which ionize in water to give H+ and anions in water.
What is an Arrhenius base?
A base which ionizes to give OH- ions and cations in water.
What is a Brønsted-Lowry acid?
An acid that donates H+ ions in a reaction.
What is a Brønsted-Lowry base?
A base that accepts H+ in a reaction.
What is a Lewis acid?
A lone pair acceptor.
What is a Lewis base?
A lone pair donor.
What process and property does water have?
Autoionisation and amphoteric.
What is the reaction of boronic acid, B(OH)3 with water?
B(OH)3 + 2H2O -> H3O+ + B(OH)4-
State the strength of the conjugate base of a weak acid.
Strong
How can a greater distinction between the strength of strong acids be made?
If water is being used as the solvent, solvent levelling will occur. For greater distinction, use a weak acid which is harder to acidify.
When can we not assume [H3O+]=[A-]?
When in very dilute solution
What assumption can me made for very weak acids in the Ka equation?
[HA]initial=[HA]final, using [HA]initial-[H3O+] will be more accurate.
How do you work out the degree of dissociation?
([H3O+]/[HA]initial)x100
What is the equation relating Ka, Kb and Kw?
Ka+Kb=Kw(=14@298K)
What is the trend for the acidity of the hydrogen halides and what are the 2 reasons this trend occurs?
HI>HBr>HCl>HF
- The H-X bond becomes weaker down the group
- The stability and reactivity of X-, the higher the charge density of X-, the more stable it is in water(favouring F-) but if it has a high charge density, it can stop H3O+ moving freely so it lowers the acidity
What 2 features to oxo acids have?
O-H and E=O bonds
If an oxo acid is dibasic what does the structure contain?
2 O-H groups
What is Bell’s rule?
For the acid HmEOn, pKa~8-5(n-m) n-m denotes the number of E=O groups
How do halogenated organic acids compare in acidity to regular organic acids and why?
Halogenated organic acids are more acidic as halogens are electronegative which draws electron density towards it and makes carbons partially positive so a negative charge of a conjugate base is better stabilised.
What process can happen to Fe(OH)3(OH2)3(s)?
It can be dehydrated to Fe2O3(s)
Why is hydrated Al3+ a weaker acid than hydrated Fe3+?
Transition metals make stronger metal-oxygen bonds than other metals and the conjugate bases of iron can dimerise, increasing its stability.
What are the 2 products of Al2O3 reacting amphoterically?
[Al(OH)4]- and [Al(OH2)4(OH)2]+
What is the Henderson-Hasselbach equation?
pH=pKa+log([A-]/[HA])
What is a back titration?
Where you react a substance with an excess of acid/base, then react the remaining acid/base to work how much is left and therefore how much of the substance there was.
What will a weak acid/strong base titration graph look like and where is the equivalence point? Why is there a change in the pH of the equivalence point?
The lower half of the graph will move up with an equivalence point pH>7. When the acid has been neutralised the strong conjugate base remains in solution, making the solution basic
How do you find the equivalence pH of successive ionisations of an acid?
Find the average of the 2 pKa values
If an indicator is represented as HIn, when would you expect the colour of the solution to change? When does the colour actually change?
When [HIn]=[In-], at pH=pKin. When there is a 10:1 ratio of one form to the other form, this means the pH usually changes over 2 pH units.
For amino acids, what is pI occur? How can this be tested?
The pH when an amino acid is favoured as the zwitterion with no charge. This can be tested with electrophoresis.
