salts in solution
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Salts in Solution. Hydrolysis and Buffers. Introduction. Strong acids added to water produce a weak conjugate base . HCl(g) + H 2 O(l) ➜ Cl - (aq) + H 3 O + (aq). strong acid. weak base. Strong bases added to water produce a weak conjugate acid . NaOH(s) ➜ Na + (aq) + OH - (aq). - PowerPoint PPT PresentationTRANSCRIPT
Salts in SolutionHydrolysis and Buffers
IntroductionStrong acids added to water produce a weak conjugate base.
HCl(g) + H2O(l) ➜ Cl-(aq) + H3O+(aq)strongacid
weakbase
Strong bases added to water produce a weak conjugate acid.
NaOH(s) ➜ Na+(aq) + OH-(aq)strongbase
weakacid
IntroductionWeak acids added to water produce a relatively strong conjugate base.
HNO2(aq) + H2O(l) ➜ NO2-(aq) + H3O+
(aq)weakacid
strongbase
Weak bases added to water produce a relatively strong conjugate acid.
NH3(aq) + H2O(l) ➜ NH4+(aq) + OH-(aq)
weakbase
strongacid
Salt HydrolysisWhen acids and bases become involved in neutralizations, they form salts and water.
HNO2(aq) + NaOH(aq) ➜ NaNO2(aq) + H2O(l)nitrous
acidsodium
hydroxide
HCl(aq) + NH3(aq) ➜ NH4Cl(aq)hydrochloric
acidammonia
sodiumnitrite
water
ammoniumchloride
HCl(aq) + NaOH(aq) ➜ NaCl(aq) + H2O(l)hydrochloric
acidsodium
hydroxidesodiumchloride
water
Salt HydrolysisWhen the salts themselves are dissolved in water, they hydrolyze.
NaNO2(aq) ➜ Na+(aq) + NO2-(aq)
sodiumnitrite
sodium
NH4Cl(aq) ➜ NH4+(aq) + Cl-(aq)
ammoniumchloride
ammonium
nitrite
chloride
NaCl(aq) ➜ Na+(aq) + Cl-(aq)sodiumchloride
sodium chloride
Salt HydrolysisThe ions that are weak conjugate acids and bases have no other effect on the solution.
cations(weak conjugate acids)
anions(weak conjugate bases)
sodium, Na+ chloride, Cl-
potassium, K+ nitrate, NO3-
calcium, Ca2+ bromide, Br-
strontium, Sr2+ chlorate, ClO3-
Salt HydrolysisThe ions that are relatively strong conjugate acids and bases have effects on the solution.
cations(strong conjugate acids)
anions(strong conjugate bases)
ammonium, NH4+ acetate, CH3COO-
methylaminium, CH3NH3+ nitrite, NO2
-
pyridinium, C5H5NH+ fluoride, F-
ethylaminium, CH3CH2NH3+ hypochlorite, ClO-
Salt HydrolysisStrong conjugate acids hydrolyze in solution, donate hydrogen ions, and lower the pH.
NH4+(aq) + H2O(l) ➜ NH3(aq) + H3O+(aq)
Strong conjugate bases hydrolyze in solution, accept hydrogen ions, and raise the pH.
CH3COO-(aq) + H2O(l) ➜ CH3COOH(aq) + OH-
(aq)
Salt HydrolysisIf we have a salt which results from the neutralization of a strong acid and a strong base
the resulting solution is neutral.
NaCl(aq) ➜ Na+(aq) + Cl-(aq)
Na+(aq) + H2O(l) ➜ no reaction
Cl-(aq) + H2O(l) ➜ no reaction
Salt HydrolysisIf we have a salt which results from the neutralization of a strong acid and a weak base
the resulting solution is acidic.
NH4Cl(aq) ➜ NH4+(aq) + Cl-(aq)
NH4+(aq) + H2O(l) ➜ NH3(aq) + H3O+(aq)
Cl-(aq) + H2O(l) ➜ no reaction
Salt HydrolysisIf we have a salt which results from the neutralization of a weak acid and a strong base
the resulting solution is basic.
NaClO(aq) ➜ Na+(aq) + ClO-(aq)
Na+(aq) + H2O(l) ➜ no reaction
ClO-(aq) + H2O(l) ➜ HClO(aq) + OH-(aq)
Salt HydrolysisIf we have a salt which results from the neutralization of a weak acid and a weak base
the resulting solution may be acidic, basic, or neutral.
It depends on the relative strengths of the acid and base.
NH4ClO(aq) ➜ NH4+(aq) + ClO-(aq)
NH4+(aq) + H2O(l) ➜ NH3(aq) + H3O+(aq)
ClO-(aq) + H2O(l) ➜ HClO(aq) + OH-(aq)
BuffersA buffer is a solution in which the pH remains relatively constant when small amounts of acid or base are added.
A buffer is prepared with a solution of
a weak acid and one of its salts
CH3COOH and NaCH3COO
a weak base and one of its salts
NH3 and NH4Cl
BuffersBuffers are better able to resist pH changes than is pure water.
Add 10 mL of 0.1 M HCl to 50 mL of
pure water
pH goes from 7.00 to 1.78 (∆pH = 5.22)
acetic acid/acetate buffer
pH goes from 4.74 to 4.57 (∆pH = 0.18)
BuffersThe equilibrium set up between the acetic acid (CH3COOH) and its acetate salt (CH3COO-) allows the solution to absorb excess acid or base.
H3O+ + CH3COO- ⇄ CH3COOH + H2O
OH- + CH3COOH ⇄ CH3COO- + H2O
The concentrations of the acid and the salt act as reservoirs of neutralizing power.
BuffersA buffer cannot control pH when too much acid or base is added.
The reservoirs of neutralizing power are used up.
When this happens, we exceed the buffering capacity of the system.
Our bodies keep blood at pH = 7.35-7.45 using
carbonic acid/hydrogen carbonate
dihydrogen phosphate/hydrogen phosphate