Acids and Bases Flashcards
why arrhenius’ theory is not solid
- it cannot explain why substances without OH- like NH3 act as bases
- does not take account the role of solvent
- does not describe accurately the H+ ion state as it does not exist but exists as H3O+
what is the name of the compound that results from the reaction of a Lewis base and a Lewis acid?
lewis adduct
amphoteric substances
substances that can act as both acids and bases
water as an amphoteric substance
water donates H+ when it reacts with a stronger base
water accepts H+ when it reacts with a stronger acid
dissociation of carbonic acid
carbonic acid is a diprotic acid
H2CO3 + H20 –><– H3O+ + HCO3-
HCO3- is a weak acid a second dissociation can take place:
HCO3- + H20 –><– H3O+ + CO3 2-
dissociation of sulfuric acid
H2SO4 + H2O –> H3O+ + HSO4-
HSO4- + H20 –><– H3O+ + SO4 2-
what happens to the conjugate base as the strength of the acid decreases
the strength of the conjugate base increases
how can we determine the direction of the reaction
in any acid-base reaction, we have 2 acids and 2 bases; however, one acid is stronger than the other base. by comparing their relative strength, we can determine the direction of the reaction
why is water omitted from the expressions involving dissociation?
because the concentration of water in water is 55.5 mol and when we add acid, the conc of water barely changes
what does the equilibrium constant depend on?
temperature
antacids
substances that are used to neutralise excess acid. they are made up of Al(OH)3 and Mg(OH)2 mixtures. these hydroxides are not very soluble in water so the levels of OH- are not damaging to the intestinal tract
equation for strong acids
[H3O+] = Ca (initial)
equation for weak acids
H3O+ = square root( Ka x Ca)
equation for weak base
OH- = square root( Kb x Cb)
ionisation energies for polyprotic acids
1st ionization energy is the strongest because once you have a negative charge on an ion, pitting another negative charge on that ion by releasing a proton is more difficult
what happens to the acid-base equilibria as you add acid?
when adding acid, the equilibrium shifts to the left.
what happens to the acid-base equilibria as you add OH-?
the equilibrium shifts to the right
acid-base titration
a known volume of acid is placed in a flask with an indicator and titrated with a measured volume of a base solution, such as NaOH, to the neutralization endpoint
the endpoint of the titration
- the moles of the base= moles of the acid
- concentration of the base is known
- The volume of the base used to reach the endpoint is measured
- molarity of the acid is calculated using the neutralisation equation for the reaction
buffer
a solution that resists changes in pH when small amounts of acid or base are added
why are buffers important for proteins
because proteins lose their 3D structure as they are sensitive to pH changes because of an interruption of hydrogen bonds, dipole-dipole, and van der Waals.
what are the constituents of a buffer solution?
of a weak acid and a conjugate base in similar concentrations or a weak base and its conjugate acid.
addition of a base to a buffer solution
the small amount of base that is added is neutralised by the weak acid shifting the equilibrium in the direction of the products
addition of an acid to a buffer
the additional H3O+ combines with the conjugate base ion causing the equilibrium to shift in the direction of the reactants
