Which combination is the best choice to prepare a buffer with a ph of 5.0? which combination is the best choice to prepare a buffer with a of 5.0? hcho2; nacho2 (pka for hcho2 is 3.74) c5h5n; c5h5nhcl (pkb for c5h5n is 8.76) nh3; nh4cl (pkb for nh3 is 4.75) hno2;nano2 (pka for hno2 is 3.33)?

The best combination is C5H5N; C5H5NHCl (pKb for C5H5N is 8.76)

Explanation:

Step 1: Data given

pH of a buffer = pKa + log ([A-]/[HA])

pH of a buffer = pKb + log ([B+]/[BOH])

Step 2

hcho2; nacho2 (pka for hcho2 is 3.74)

⇒ HCHO2 = CH2O2 = formic acid = a weak acid

⇒ NaCHO2

⇒ pKa = 3.74

pH = 3.74 + log [HCOO-] / [HCOOH]

When the amount of HCHO2 and NaCHO2 is the same, the pH is 3.74

c5h5n; c5h5nhcl (pkb for c5h5n is 8.76)

⇒ C5H5N = base

⇒ C5H5NH+ = conjugate acid

⇒ pKb = 8.76

pOH = pKb + log [conjugate acid]/[weak base]

pOH = 8.76 + log [C5H5NH+]/[C5H5N]

When the amount of C5H5N and C5H5NCl is the same, pOH is 8.76

pH = 14 - 8.76 = 5.24

nh3; nh4cl (pkb for nh3 is 4.75)

⇒ NH3 = base

⇒ NH4+ = conjugate acid

⇒ pKb = 4.75

pOH = 4.75 + log [NH4+]/[NH3]

When the amount of NH4Cl and NH3 is the same, pOH is 4.75

pH = 14 - 4.75 = 9.25

hno2;nano2 (pka for hno2 is 3.33)?

⇒ HNO2 = a weak acid

⇒ NO2-

⇒ pKa = 3.33

pH = 3.33 + log [NO2-] / [HNO2]

When the amount of both is the same, the pH will be 3.33

The best combination is C5H5N; C5H5NHCl (pKb for C5H5N is 8.76)

the volume increases