pH, pOH, Buffers, Equilibrium Flashcards
What’s equilibrium
The rates of the forward and reverse reaction are equal, so the concentrations of products and reactants don’t change. We consider the reaction “over” bc they are moving forward & backward at the same pace (constantly).
What’s a buffer?
A solution that resists changes in pH even when a strong acid or base is added
It’s made of a weak acid and its conjugate base
when do you use -log?
when you know the concentration (or molarity)
when do you use 10^-
when you know the pH or pOH
why must a buffer by made from a weak acid and its conjugate base?
If it was a strong acid, it would dissociate 100% completely and contribute to the h30+ concentration. Allows the weak acid which doesnt dissociate to be available to react with added base without adding h30+ to the solution in general.
why does the pH not change when a strong base or acid is added to the buffer?
strong base reacts with the weak acid
HC2H3O2 + NaOH -> H2O + C2H3O2- + Na+
strong acid reacts with conjugate base
C2H3O2- + HCl -> HC2H3O2 + Cl-
pH measures
potential of hydrogen measure h30+ concentration
pOH
potential of hydroxide measures OH- concentration
Are all chemical reactions reversible?
technically yes
what does it mean to be neutral?
equal amounts of h3o+ and OH- concentration
What reacts with what when involving a buffer?
strong base reacts with weak acid
weak acid reactions with conjugate base
what does it mean to reach equilibrium?
the reactions keeps going (doesnt stop). theres no change in concentration so its called equilibrium
what does it mean to reach equilibrium?
the reactions keeps going (doesnt stop). theres no change in concentration so its called equilibrium
in the reaction, what does it mean if there is onlyt a forward arrow?
it indicates that the reaction has reached equilibrium
why is the pH scale 1-14
because when water dissociation reaches equilibrium, the concentrations equal 10^-14
strong acids or bases when calculating pH/pOH
they dissociate 100%, we dont consider the reverse reaction so we just calculate pH and pOH using the acid/base concentration as the H+ or OH- respectively (allowed to plug in molarity because of that)
-no reverse reaction
weak acids and bases when calculating pH/ pOH
equilibrium constants (ka and kb) can be used to determine how much an acid or base dissociates into ions by comparing how much product is formed to how much reactant remains. This can let you find pH and pOH of weak acids and bases by giving you a h3o+ and OH- concentration
weak acids and bases formula
how much reactant left
this equals how much an acid or base dissociates
(this is all calculated one its reached equilibrium)
weak acids and bases formula
how much reactant left
this equals how much an acid or base dissociates
(this is all calculated one its reached equilibrium)
Dissociation of strong acids and bases vs weak
strong dissociate 100% so 2 M HCl or NaOH has an H+ or OH- concentration equal to 2M
weak do not dissociate 100% and therefore must be told the H+ or OH- concentration
Smaller concentration of H+ equals ________
higher pH (lower values) 1 is most acidic, 14 is least
Smaller concentration of H+ equals ________
higher pH (lower values) 1 is most acidic, 14 is least
affinity of the acetate ion for protons compared to water molecules for protons?
the Acetate doesnt give up its H’s very easily bc it dissociates less than 100% so the weak acid is very good at holding onto its protons compared to water molecules
