Question
Using a table of pka values:
2) Determine the volume (in mL) of 0.688 M nitric acid (HNO3) that must be added to 736 mL of 0.0498 M sodium hydrogen citrate (Na2C3H5O(COOH)(COO)2) to yield a pH of 4.43.
Assume the 5% approximation is valid and report your answer to 3 significant figures.
Table 10.2: pKa and pKb values at 25 °C for some common weak acids and their conjugate bases pKaConjugate base 0.20 FCCOo 0.66 Cl3 CCoo 1.23 HOOCCOO 1.30 CI2HCCOO 1.77 HS03 1.92 So- 1.95 CIO2 2.12 H2P0 2.87 CIH2CCOO 2.90 BrH2CCOO 3.08 C2HoCOO 3.13 C3H5O(COOH)2COO dihydrogen citrate ion10.87 Acid name trifluoroacetic acid trichloroacetic acid oxalic acid dichloroacetic acid Acid formula F3CCOOH Cl CCOOH HOOCCOOH CI2HCCOOH Conjugate base name trifluoroacetate ion trichloroacetate ion hydrogen oxalate ion dichloroacetate ion hydrogen sulfite ion sulfate ion chlorite ion dihydrogen phosphate ion chloroacetate ion bromoacetate ion lactate ion 13.80 13.34 12.70 12.23 12.08 sulfurous acid hydrogen sulfate ion chlorous acid phosphoric acid chloroacetic acid bromoacetic acid lactic acid citric acid hydrofluoric acid nitrous acid acetylsalicylic aci formic acid ascorbic acid hydrogen oxalate ion benzoic acid HCIO H3PO CIH2CCOOH BrH2CCOOH 11.88 10.92 C3Hs O(COOH)3 10.80 10.63 10.52 fluoride ion nitrite ion acetvlsalicylate ion formate ion ascorbate ion oxalate ion benzoate ion phenylamine (aniline) HNO 3.37 NO2 3.48 CH,O2COo 3.75 HCOO 4.10CH,OCOO 4.19ooccoO 4.20 C6H5COO HCOOH 9.81 C&H;, COOH phenylammonium ionHsNH3 4.63 CH,NH2 9.37
Explanation / Answer
1) Since - pOH = 14 - pH = 14 - 5.18 = 8.82, [OH-] = 10-pOH = 1.513*10-9 M
Thus, pOH = pKb + log [salt] / [base]
8.82 = 8.75 + log (0.338/base)
C5H5N = 0.287 M
Mass of pyridine to be added to get the given pH = (0.287 mol/L)(*0.333 L )(79 g/mol) = 7.55 g
2) DATA of pKa values of citric acid were not provided in the question.
