a) H3PO4 - acidic
H3PO4 = 3H+ + PO43-
H3PO4 + 3NaOH = Na3PO4 + 3H2O
pH = 1/2pKa,H3PO4 - 1/lgCH3PO4 = 1/2*2.15 - 1/2*lg(0.05) = 1.7
b) NaH2PO4 - both acidic and basic
NaH2PO4 = Na+ + H2PO4-
NaH2PO4 + 2NaOH = Na3PO4 + 2H2O
NaH2PO4 + HCl = H3PO4 + NaCl
pH = 1/2pKa,H3PO4 + 1/2pKa,H2PO4- = 1/2*2.15 + 1/2*7.21 = 4.7
c) Na2HPO4 - both acidic and basic
Na2HPO4 = 2Na+ + HPO42-
Na2HPO4 + NaOH = Na3PO4 + H2O
Na2HPO4 + 2HCl = H3PO4 + 2NaCl
pH = 1/2pKa,H2PO4- + 1/2pKa,HPO42- = 1/2*7.21 + 1/2*12.3 = 9.8
d) Na3PO4 - basic
Na3PO4 = 3Na+ + PO43-
PO43- + H2O = HPO42- + OH-
pH = 14 - 1/2pKb,PO43- + 1/2lgCPO43- = 14 - 1/2*1.7 + 1/2lg(0.05) = 12.5
pKb,PO43- = 14 - pKa,HPO42- = 14 - 12.3 = 1.7
e) NH4Cl - acidic
NH4Cl = NH4+ + Cl-
NH4+ + H2O = NH3 + H3O+
pH = 1/2pKa,NH4+ - 1/2lgCNH4+ = 1/2*9.25 - 1/2*lg(0.05) = 5.3
pKa,NH4+ = 14 - pKb,NH3 = 14 - 4.75 = 9.25
f) NaC6H7O7 - both acidic and basic
NaC6H7O7 = Na+ + C6H7O7-
NaC6H7O7 + 2N7aOH = Na3C6H5O7 + 2H2O
NaC6H7O7 + HCl = C6H8O7 + NaCl
pH = 1/2pKa,H2A + 1/2pKa,HA- = 1/2*2.92 + 1/2*4.28 = 3.6
g) C6H5OH - acidic
C6H5OH = C6H5O- + H+
C6H5OH + NaOH = C6H5ONa + H2O
pH = 1/2pKa,C6H5OH - 1/2lgCC6H5OH = 1/2*10 - 1/2*lg(0.05) = 5.65
h) NaHCO3 - both acidic and basic
NaHCO3 = Na+ + HCO3-
NaHCO3 + NaOH = Na2CO3 + H2O
NaHCO3 + HCl = H2CO3 (CO2 + H2O) + NaCl
pH = 1/2pKa,H2CO3 + 1/2pKa,HCO3- = 1/2*6.35 + 1/2*10.32 = 8.3
i) Na2C4H4O4 - basic
Na2C2H2O4 = 2Na+ + CH4O42-
C2H4O42- + 2H2O = C2H6O4 + 2OH-
pH = 14 - 1/2pKb,C2H4O42- + 1/2lgCC2H4O42- = 14 - 1/2*8.36 + 1/2lg(0.05) = 9.2
pKb,C2H4O42- = 14 - pKa,C2H5O2- = 14 - 5.64 = 8.36
j) C4H9O3NH3Cl - acidic
C4H9O3NH3Cl = C4H9O3NH3+ + Cl-
C4H9O3NH3+ = C4H9O3NH2 + H+
pH = 1/2pKa,C4H9O3NH3+ - 1/2lgCC4H9O3NH3+ = 1/2*8.075 - 1/2*lg(0.05) = 4.7
k) CH3NH2 - basic
pH = 14 - 1/2pKb,CH3NH2 + 1/2lgCCH3NH2 = 14 - 1/2*3.34 + 1/2lg(0.05) = 11.7
Comments
Please the concentration is 0.05M but not 0.5M
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