Answer:
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)
