Lecture 19.5- Buffers & salts HONORS

19.3

Previously, on HCHEM….

THE LARGER THE Ka THE STRONGERTHE ACID!!

The larger the Kb the more dissociationoccurs, so the stronger the base.

The conjugates of weak acids & basesare strong.

Salts can be acidic or basic if one of theions is a conjugate of something weak.

19.5

Salts can be acidic or basic if one of theions is a conjugate of something weak.

Ex.NH4Cl is an acidic salt because NH4

+ isthe conjugate of a weak base.

19.5

Salts can be acidic or basic if one of theions is a conjugate of something weak.

Ex.NH4Cl is an acidic salt because NH4

+ isthe conjugate of a weak base.

NaCH3COO is a basic salt becauseCH3COO- is the conjugate of a weakacid

19.5

To determine whether a salt solution is acidicor basic, remember the following rules:

Not because the strong ones give more ions.

In a neutralization weak acids and bases will give allof their ions because they are neutralized. (shiftsequilibrium towards dissociation)

It is because of the acid/base properties of theconjugates.

Would the following salts create acidicor basic solutions when dissolved inwater?

NaClKC2H3O2

NH4NO3

Would the following salts create acidicor basic solutions when dissolved inwater? cation anion

from base from acidNaCl weak weakKC2H3O2 weak basicNH4NO3 acidic weak

Vapors of the strong acid HCl(aq) andthe weak base NH3(aq) combine toform the acidic white salt ammoniumchloride (NH4Cl).

19.5

A buffer is a solution that resists changes inpH when moderate amounts of acids or

bases are added.

Buffer solutions are prepared by mixing a weak acid with its conjugate base

ora weak base with its conjugate acid

Buffer solutions are prepared by mixing a weak acid with its conjugate base

ora weak base with its conjugate acid

Buffers can neutralize both OH– and H+

when one of these ions is added to thebuffered solution.

A buffer solution can be prepared byusing the weak base ammonia, NH3, and

an ammonium salt, such as NH4Cl.

A buffer solution can be prepared byusing the weak base ammonia, NH3, and

an ammonium salt, such as NH4Cl.

• When acid is added, NH3 reacts with H+.NH3 + H+ NH4

+

A buffer solution can be prepared byusing the weak base ammonia, NH3, and

an ammonium salt, such as NH4Cl.

• When acid is added, NH3 reacts with H+.NH3 + H+ NH4

+

• If a base is added, the NH4+ ion from the

salt reacts with the OH–.NH4

+ + OH- NH3 + H2O

Another buffer system contains the weakacid acetic acid, HC2H3O2, and the salt

sodium acetate, NaC2H3O2.

Another buffer system contains the weakacid acetic acid, HC2H3O2, and the salt

sodium acetate, NaC2H3O2.

• If base is added, the weak acid reacts toneutralize the addition.HC2H3O2 + OH- C2H3O2

- + H2O

Another buffer system contains the weakacid acetic acid, HC2H3O2, and the salt

sodium acetate, NaC2H3O2.

• If base is added, the weak acid reacts toneutralize the addition.HC2H3O2 + OH- C2H3O2

- + H2O

• If acid is added, the acetate ion from theNaC2H3O2 will neutralize the added H+.C2H3O2

- + H+ HC2H3O2

The buffer capacity is theamount of acid or base thatcan be added to a buffersolution before a significantchange in pH occurs.