TBR Buffer Question

[vanillabear55]

Which does NOT produce a buffer?

A. H3CCO2H with 2 equivalents of H3CCO2K
B. NH3 with 2 equivalents of NH4Cl
C. H2CO3 with 1.5 equivalents of KOH
D. H3CNH2 with 1.5 equivalents of HCL

The answer is D, but I'm really confused why and how to figure out the others ARE buffers, the TBR explanation failed me, specifically...can someone explain how A/B qualify as buffers? When I did this question they seemed like they're in a 1:2 ratio....I'm assuming theres a conversion of one to the other upon mixing but I don't have a clue what is is....thanks

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[Cawolf]

A buffer is a solution comprised of a weak acid and it's conjugate base or a weak base and it's conjugate acid.

These can also be formed by mixing a weak acid with a strong base (to produce an equivalent amount of conjugate base by deprotonating the acid) or a weak base with a strong acid (to produce the conjugate acid by protonating the weak base).

An ideal buffer would have a ratio of 1:1, but anything up to 10:1 can still provide some buffering ability +/- 1 pH.

A is acetic acid in a 1:2 ratio with acetate - buffer.

B is ammonia in a 1:2 ratio with ammonium - buffer.

C is carbonic acid with a strong base. The 1.5 equiv of hydroxide will convert all of the H2CO3 into a 1:1 mixture of CO3 2- and HCO3-. This mix is a buffer.

D is methylamine (go breaking bad!), a weak base. When you add 1.5 equiv of strong acid, it will protonate all of the methylamine, and have excess HCl remaining. There is no ratio, it is not a buffer.

The reason C forms a buffer is that the initial acid is diprotic, where methylamine can only accept one proton.

 

[vanillabear55]

A buffer is a solution comprised of a weak acid and it's conjugate base or a weak base and it's conjugate acid.

These can also be formed by mixing a weak acid with a strong base (to produce an equivalent amount of conjugate base by deprotonating the acid) or a weak base with a strong acid (to produce the conjugate acid by protonating the weak base).

An ideal buffer would have a ratio of 1:1, but anything up to 10:1 can still provide some buffering ability +/- 1 pH.

A is acetic acid in a 1:2 ratio with acetate - buffer.

B is ammonia in a 1:2 ratio with ammonium - buffer.

C is carbonic acid with a strong base. The 1.5 equiv of hydroxide will convert all of the H2CO3 into a 1:1 mixture of CO3 2- and HCO3-. This mix is a buffer.

D is methylamine (go breaking bad!), a weak base. When you add 1.5 equiv of strong acid, it will protonate all of the methylamine, and have excess HCl remaining. There is no ratio, it is not a buffer.

The reason C forms a buffer is that the initial acid is diprotic, where methylamine can only accept one proton.

hahahah omg this cracked me up...it's getting too late to be studying

thanks so much!