Acid-base buffers are most effective when the target pH of the buffer solution i

Question

Acid-base buffers are most effective when the target pH of the buffer solution is close (within one unit) to the pKa of the conjugate acid in in the conjugate acid/base pair to be used in the buffer. This is called the buffer range for a particular acid/base system.

For the three questions below, select the two compounds from the list which could be most effectively combined to create a buffer at the target pH. You will not need to use all of the compounds - and should need to use each compound only once.

ammonia, NH3

sodium formate, Na(HCOO)

sodium hypochlorite, NaCO

sodium acetate, Na(CH3COO)

ammonium chloride, (NH4)C

pyridine, C5H5N

pyridinium chloride, (C5H5NH)C

hypochlorous acid, HCO

formic acid, HCOOH

ammonia, NH3

sodium formate, Na(HCOO)

sodium hypochlorite, NaCO

sodium acetate, Na(CH3COO)

ammonium chloride, (NH4)C

pyridine, C5H5N

pyridinium chloride, (C5H5NH)C

hypochlorous acid, HCO

formic acid, HCOOH

Explanation / Answer

Buffer = Buffer is composed of large of amount of weak acid/weak base and its salt with strong base/strong acid.

pH = pKa + log(salt/acid)

pOH = pKb + log(salt/base)

In the above given weak base NH3, the suitable salt is NH4Cl

NH3 + NH4Cl is a good buffer.

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