5.1.3 Acids, Bases And Buffers Flashcards
what is a Bronsted-Lowry Acid or Base?
A Bronsted-Lowry acid donates protons (H+)
A Bronsted-Lowry base accepts protons (H+)
what are conjugate acid-base pairs?
A conjugate acid base pair is a substance that contains 2 species that can be interconverted
species that are linked by a transfer of a proton
e.g HCl(aq) ⇌ H+(aq) + Cl-(aq)
[forward reaction] HCl releases a proton to form conjugate base Cl-
[reverse reaction] Cl- accepts a proton to form its conjugate acid HCl
how many acid base pairs are there in an acid-base equilibrium?
what are the pairs in this reaction?
HCl(aq) + OH-(aq) ⇌ H2O(l) + Cl-(aq)
there are 2 conjugate acid-base pairs so 2 acids (acid 1/2) and 2 bases (base1/2)
HCl = acid 1 bc it donates a proton to OH- so OH- = Base 2 as it accepts a proton
H2O = acid 2 bc it donates a proton to Cl- so Cl- = base 1
THERE CANNOT BE 2 ACIDS/BASES ON THE SAME SIDE, NOR CAN ACID1 AND BASE1 BE ON THE SAME SIDE AND VISEVERSA
What are monobasic, dibasic and tribasic acids?
Monobasic- can donate 1 H+
Dibasic - can donate 2 H+
Tribasic can donate 3 H+
What volume of 0.1 M HCl (monobasic acid) will neutralise 25cm3 of 0.1M NaOH?
25cm3 of HCl because 1 H+ (from HCl) ion neutralises 1 OH- (from NaOH) ion as HCL is monobasic
What volume of 0.1 M H2SO4 (monobasic acid) will neutralise 25cm3 of 0.1M NaOH?
25÷2 because H2SO4 is dibasic and so for each molecule of acid it can dissociate 2 H+ ions and so Neutralise 2 NaOH and so its 12.5cm3 H2SO4
What volume of 0.1 M H3PO4 (monobasic acid) will neutralise 25cm3 of 0.1M NaOH?
25÷3 because H3PO4 is a tribasic acos and so can dissasociate 3 H+ ions into solution so each H3PO4 can neutralise 3 NaOH so = 8.33cm3 H3PO4
How do you turn the reactions of acids (e.g with metal oxides, carbonates and Alkalis) into ionc equations?
Look at the full equation and cancel out any spectator ions and add in charges and state symbols
e.g
2HCl(aq) + Mg(aq) → MgCl2(aq) + H2(g)
Ionic equation:
2H+(aq) + Mg(s) → Mg2+(aq) + H2(g)
what does the pH scale tell us in terms of H+ ions?
-A low value of [H+] matches a high value of pH -A high value of [H+] matches a low value of pH -pH is a logarithmic scale for measuring the [H]+ in solution. -Each increasing pH value is a magnitude of 10 smaller.
so: pH = -log[H+(aq)]
and: [H+(aq)] = 10^-pH
how do you calculate pH from H+ ion concentration?
pH = -log[H+(aq)]
how do you calculate H+ ion concentration from pH
[H+(aq)] = 10^-pH
How do you calculate the pH of strong acids?
solve this:
HA(aq) → H+(aq) + A-(aq)
[HA]=1.35 x 10^-2moldm-3?
[Hint] Strong acid HA completely dissociates
since HA completely dissociates, the conc of HA = conc of H+ since all H+ came from HA
so pH of HA = -log(1.35 x 10^-2 )
= 1.87
How does diluting a solution have an effect on pH?
changing the concentration
(e.g diluting an acid/base)
can have an effect on the pH as A pH of 1 has 10 times the concentration of H+ ions as a solution of pH 2.
e.g
50cm3 of 0.1M hydrochloric acid is diluted TO A TOTAL VOLUME of 100cm3, what is the pH change?
0.1M has been halved to 0.05M
pH = -log[0.1] = 1
pH = -log[0.05] = 1.3
what is the relationship between Ka and pKa
pKa = -log Ka
Ka = 10^pKa
how do you find the new concentration in a dilution calculation?
e.g. find the pH of HCl if it’s 5cm3 of 0.025moldm-3 and is diluted to 100cm3?
do (original volume/new volume) = 5/100
Multiply this by the concentration = 0.05 x 0.025 = 1.25x10-3 moldm-3
then since [H+] = [HA] find the pH =-log 1.25x10-3 moldm-3 = 2.9