CHEM1011 Lecture Notes - Lecture 29: Buffer Solution, Weak Base, Sodium Hydroxide
9 Jun 2018
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Lecture 29: Buffers
Salts of weak acids and bases
- Is a solution of NaCN acidic of basic?
NaCN is the salt of NaOH stog ase ad HCN eak aid. The ase is: pH
>7
Overall reaction is:
- Does a solution of NH4Cl have pH > 7 or <7?
Salt of NH4OH (weak base) and HCl (strong acid)
Acid wins: pH < 7 and reaction is
The common ion effects
If you add the salt of an acid to a solution of the same acid, then the equilibrium will shift
towards neutral.
Addition of CH3COONa will boost [CH3COO-]
By Le Chatelies piiple, the euiliiu ill shift to the left to eoe CH3COO- and
therefore decrease [H3O+]
The same holds true for a base: if you add the salt of a base to a solution of the same base then
the equilibrium, will shift towards neutral
Buffer system
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Document Summary
Nacn is the salt of naoh (cid:894)st(cid:396)o(cid:374)g (cid:271)ase(cid:895) a(cid:374)d hcn (cid:894)(cid:449)eak a(cid:272)id(cid:895). Salt of nh4oh (weak base) and hcl (strong acid) Acid wins: ph < 7 and reaction is. If you add the salt of an acid to a solution of the same acid, then the equilibrium will shift towards neutral. By le chatelie(cid:396)(cid:859)s p(cid:396)i(cid:374)(cid:272)iple, the e(cid:395)uili(cid:271)(cid:396)iu(cid:373) (cid:449)ill shift to the left to (cid:396)e(cid:373)o(cid:448)e ch3coo- and therefore decrease [h3o+] The same holds true for a base: if you add the salt of a base to a solution of the same base then the equilibrium, will shift towards neutral. Consider change in ph of 1. 0l of pure water (ph= 7. 00) if we add an amount of 1. 0 x 10-3 mol hcl: Consider a buffer solution with 0. 100m each of sodium acetate (naac) and acetic acid (hac; ka= 10-4. 76) For a buffer solution, which contains similar concentrations of conjugate acid/base pair of a weak acid:
