Acids and Bases Flashcards
Amphoteric and example
Can act as either an acid or a base.
Eg. Water
Dissociation constant for water
Kw, ionic product.
Dissociation constant, Kw equation
Kw = [H30+][OH-]
Kw value at 25°C
1*10^-14
Relationship between pH and hydrogen ion concentration
pH=-log10[H30+]
[H30+] = 10^-pH
Brønsted-Lowry definition of acids and bases
Acid is a proton donator and base is a proton acceptor.
For every acid there is a….
Conjugate base formed when a proton lost.
For every base there is a ….
Conjugate acid formed when a proton is gained
What do strong acids and bases do in solution?
Completely dissociate into ions.
What do weak acids do in solution?
Partially dissociate into ions.
Strong acid examples
Hydrochloric, sulfuric and nitric acid.
Weak acid examples
Ethanoic, carbonic and sulforous acid.
Strong base examples
Metal hydroxides.
Weak base examples
Ammonia and amines.
Similarities and differences between weak and strong acids/bases
Differences - pH, conductivity and reaction rates.
Similarities - Stoichiometry e.g. in titration weak bases neutralises strong acid.
Approx pH of weak acid equation
pH=1/2pKa-1/2log10c
Salt pH explanation
Draw out equilibrium equation of water and draw out dissociation equation of salt. Each of the dissociated salt ions will react with the water ions. Weak one will form equilibrium but strong will not as once it turns into strong acid or base it will immediately dissociate. Since the weak acid or alkali has set up an equilibrium it is removing hydroxide or hydrogen ions from the equilibrium and adding water to it. Subsequently shifting water equilibrium to the right producing more base or acid.
Buffer solution definition
A solution that remains relatively constant pH despite small amounts of acids, bases or water being added.
What does an acid buffer solution consist of?
A weak acid and one of its salts made from a strong base
What does a basic buffer solution consist of?
A weak base and a salt of its base made from a strong acid.
How does an acidic buffer solution work?
Weak acid will provide hydrogen ions when these are removed by the addition of a small amount of base. The salt will provide the conjugate base which can absorb the excess hydrogen ions produced by the addition of a small amount of acid.
How does a basic buffer solution work?
Weak base removes excess hydrogen ions and conjugate acid provided by the salt supplies the hydrogen ions when these are removed.
Approx buffer pH equation
pH=pKa -log10(acid/salt)
Indicators are ..
Weak acids
Indicator dissociation equation
HIn(aq) + H2O(l) <=> H30+(aq) + In-(aq)
How is the colour of an indicator determined?
By the ratio of HIn to In-
pH range over which a colour change occurs can be estimated by the equation
pH = pKin +-1
