acids and bases Flashcards
litmus paper in acids
turns blue litmus paper red
litmus paper in bases
turns red litmus paper blue
Arrhenius acids
a substance that produces H + ions in aqueous solutions
Arrhenius base
a substance that produces OH- ions in aqueous solution
limitations of Arrhenius’s theory
- H+ does not exist in the water we always find H3O+
- only classifies acids and bases in water
- explains the basic properties of substances without OH- like NH3
bronsted lowry theory
refers to proton donors and proton acceptors
bronsted lowry acid
proton donor
bronsted lowry base
proton acceptor
amphoteric
can act as an acid or as a base
what does the strength of an electrolyte depend on?
on the extent of its dissociation into its component ions
strong electrolyte
completely dissociates into ions in solution
weak electrolyte
partially dissociates into ions in solution
what does it mean if the equilibrium lies to the right
acid is strong
what does it mean if the equilibrium lies to the left?
the acid is weak
what influences the degree to which an acid is strong or weak
the attraction between the anion of the acid and the hydrogen ion
what is the conc of water in water
55.5 mol
why do we ignore water concentration in the equilibrium constant?
because the concentration of water in water is 55.5 mol and when we add acid, the conc of water barely changes
high Ka
the equilibrium is lying on the right: strong acid
low Ka
the equilibrium lies to the left: weak acid
autoionisation of water
H20 + H20 ⇌ H3O+ +OH-
neutral
[H3O+] = [OH-]
acidic
[H3O+] > [OH-]
basic
[H3O+] < [OH-]
ionization constant for water
Kw = [H3O+] [OH-] = 10^-14 mol
pH
pH= -log[H3O+]
when does a substance behave as an acid
if it is a stronger acid than water: if its Ka is higher than Kw
Ka higher than 1
strong acid
Ka lower than 10^-14
it will behave as a base
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)
lewis acid
electron pair acceptor
lewis base
electron pair donor
buffer
resists pH change by neutralizing added acid or added base
what does a buffer consist of
of a weak acid and a conjugate base in similar concentrations or a weak base and its conjugate acid.
what do we need when we want to buffer something
a substance with a pKa close to the pH we want to buffer
Henderson Hasselbach Equation
pH = pKa + log [base]/[acid]
blood pH
7.35- 7.45
example of a buffer in biological fluids
carbonic acid/bicarbonate system:
CO2 + H2O ⇌ H2CO3
