what combination of substances will give a buffered solution that has a pH of 5.
ID: 871990 • Letter: W
Question
what combination of substances will give a buffered solution that has a pH of 5.05? (Assume each pair of substances is dissolved in 5.0 L of water.) (Kb for NH3 = 1.8 ?105; Kb for C5H5N = 1.7 ?109)
A)
1.0 mole NH3 and 1.5 mole NH4Cl
B)
1.5 mole NH3 and 1.0 mole NH4Cl
C)
1.0 mole C5H5N and 1.5 mole C5H5NHCl
D)
1.5 mole C5H5N and 1.0 mole C5H5NHCl
E)
none of these
Answer is C, why? please show work
what combination of substances will give a buffered solution that has a pH of 5.05? (Assume each pair of substances is dissolved in 5.0 L of water.) (Kb for NH3 = 1.8 ?105; Kb for C5H5N = 1.7 ?109)
A)
1.0 mole NH3 and 1.5 mole NH4Cl
B)
1.5 mole NH3 and 1.0 mole NH4Cl
C)
1.0 mole C5H5N and 1.5 mole C5H5NHCl
D)
1.5 mole C5H5N and 1.0 mole C5H5NHCl
E)
none of these
Explanation / Answer
C5H5N + H2O <----> C5H5NH+ + OH-
initial concentration
0.2 .. . . . . . .. . . . . . .. . . 0.3
at equilibrium
0.2-x. . . . . .. . . . . . . . . . 0.3+x .. . .. . x
[C5H5] = 1/ 5 = 0.2 M
[C5H5NH+] = 1.5 / 5 = 0.3 M
1.7 x 10^-9 = (0.3+x)(x) / 0.2-x
x = 1.13 x 10^-9 = [OH-]
pOH =8.95
pH =14 - pOH = 5.05
C is the answer
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