Acids & bases Flashcards
What is a Bronsted-lowry acid?
A species that donates a proton
What is a Bronsted-lowry base?
A species that accepts a proton
Whats a conjugate acid-base pair?
Contains 2 species that can be interconverted by the transfer of a proton (H+)
What is the conjugate acid-base pair for:
HCl (aq) <=> H+ (aq) + Cl- (aq)
- In the forward direction, HCl releases a proton to form its conjugate base, Cl-
- In the reverse direction, cl- accepts a proton to form its conjugate acid, HCl
What are the conjugate acid-base pairs in:
HCl (aq) + OH- (aq) <=> H2O (l) + Cl- (aq)
Acid 1 - HCl
Base 1 - Cl -
Acid 2 - H2O
Base 2 - OH-
What is a monobasic acid?
An acid that can donate a total of 1 ion per molecule of acid in an acid-base reaction
What is a dibasic acid?
An acid that can donate a total of 2 hydrogen ions per molecule of acid in an acid-base reaction
What is a tribasic acid?
An acid that can donate a total of 3 hydrogen ions per molecule of acid in an acid-base reaction
What is a spectator ion?
Ions that do not change during the reaction - they are the same in the products as they were in the reactants
2H+ + Zn ->
Zn 2+ + H2
2H+ + CuCO3 ->
Cu 2+ + H2O + CO2
2H+ + MgO ->
Mg2+ + H2O
How can the dissociation of any weak acid be shown?
HA (aq) <=> H+ (aq) + A- (aq)
For equation HA (aq) <=> H+ (aq) + A- (aq) : what is the acid dissociation constant calculated at?
Ka = [H+ (aq)] [A-(aq)] / [HA(aq)]
What temperature of Ka values usually standardised at?
25 degrees
What does the larger the Ka value mean?
- The further equilibrium is to the right
- The greater dissociation and the greater the acid strength
How do you convert between Ka and pKa?
pKa = -log10 Ka
Ka = -10^pKa
The stronger the acid, the _________ the Ka value
Larger
How do you find pH from the concentration of hydrogen ions?
pH = -log 10 [H+]
[H+] = -10^pH
What is Kw?
The ionic product of water - it has avlue of 1 x 10^-14 mol^2 dm^-6
How do you find the pH of water?
H2O (l) <=> H+(aq) + OH-(aq)
so Ka = [H+] [OH-] / [H2O]
this becomes Ka x [H2O] = [H+][OH-]
the concentration of H2O is constant so
Kw = [H+][OH-]
On dissociation, water is neutral - it produces the same number of H+ and OH- ions
so Kw = [H+]^2
[H+] = √ 1 x 10^-14 = 1 x10^-7
pH = -log 10 [H+] = 7
What is the concentration of a strong acid equal to?
Its H+ concentrations
[HA] = [H+]
What can the pH of a strong base be calculated from?
- The concentration of the base
- The ionic product of water
[H+] = Kw / [OH-]
pH = -log 10 [H+]
What does the concentration of a strong monobasic alkali equal to?
[OH-]
How can you calculate the pH of a weak acid?
- The concentration of the acid
- The Ka value of the acid
Ka = [H+] [A-] / [HA]
The equilibrium concentrations of [H+] and [A-] will be the same since one molecule of HA dissociates to each ion
Ka x [HA] = [H+]^2
pH = -log 10 [H+] = √ Ka x [HA]
What are assumptions that are made when finding concentrations and pHs?
- HA dissociates to produces equilibrium concentrations of H+ and A- that are equal ; issue is that a tiny percentage of H2O molecules dissociate so the concentrations are only roughly equal
- [HA] original = [HA] equilibrium ; issue is this means there is no dissociation but this cant be true as it must dissociate to form an acid