acids, buffers and bases Flashcards
monobasic, dibasic, tribasic acid
donates 1/2/3 H+ ion
which equation gives pH from [H+]?
pH = -log[H+]
write the Ka expression for a general weak acid HA
Ka = [H+][A-] / [HA]
which equation calculates [H+] if you know [OH-]?
[OH-]= Kw / [H+]
what does the approximation that [HA]eqm = [HA]start for a weak acid break down?
strong weak acids (lots of the [HA] will dissociate so this can’t be true)
formula and name of species made when H+ dissolves in water?
hydronium ion, H30+
how does simplified Ka= [H+] squared / [HA] rearrange to solve for [H+]?
[H+] = square root(Ka x [HA])
simplified Ka expression for weak acids
Ka = [H+] squared / [HA]
when does the approximation that [H+] = [A-] for a weak acid break down?
very dilute solutions or very wek acids (the H+ from water dissociation is significant compared with H+ from the acid)
when does the approximation that [H+] =[A-] for a week acid break down?
very dilute solution or very weak acids (H+ from water dissociation is significant compared with H+ from the
acid)
Kw expression
Kw = [H+][OH-]
how much would you need to dilute an acid solution with a pH of 1 to make it pH 4?
dilute 1 in 1000. (3 pH units means [H+] changes by a factor of 10^3 =1000)
what 2 approximations are made when calculating pH of weak acids?
[HA] at eqm is equal to that at the start and the end [H+] = [A-]
if you have a 0.5 moldm-3 solution of calcium hydroxide, what is [OH-]?
1 moldm-3 (because Ca(OH)2 is dibasic)
Kw changes with temp. Will the pH of pure water be 7 at all temperatures?
no
if Kw is 1x10^-14 at standard conditions, how does this make the pH of pure water = 7?
[H+] = root(Kw) = 1x10^-7, then pH = -log[H+] = 7
what is the name of the special constant Kw?
ionic product of water
bronsted lowry definition of base
proton acceptor
bronsted lowry definition of acid
proton donor
which equation gives [H+] from pH?
[H+] = 10^-pH
which equation gives Ka from pKa?
Ka= 10^-pKa
in the equation HCL + H20 —> H3O+ + Cl-, what do you call the pair that H2O and H3O+ make?
conjugate acid base pair
which equation gives pKa from Ka?
pKa = -log Ka
does a larger Ka mean a stronger or weaker acid?
stronger (acid dissociation eqm lies further to the right)
how are conjugate acid base pairs related?
the conjugate acid donates H+ to make the conjugate base; the base accepts H+ to make the acid
does a larger pKa mean a stronger or weaker acid?
weaker (the trend is the reverse of Ka as the equation has a negative sign: -logKa
