C. H of Buffer Solutions In the unshaded portions of the following table. supply
ID: 527524 • Letter: C
Question
C. H of Buffer Solutions In the unshaded portions of the following table. supply the calculated molarities of the indicated species in the solution mixtures. Assume the solutions are at 25 C. Note that in the rows labeled "Before Reaction," you must supply the appropri- ate concentrations after dilution occurs in the reaction mixture but before any reaction takes place. Calculated Molarities in Mixtures Haj At Equilibrium C.1 Buffer C2a Buffer HCl Before Reaction At Equilibrium C2b Buffer NaOH Before Reaction At Equilibrium At Equilibrium C.3 Water C. ia Water HCI Before Reaction At Equilibrium CAb Water NaOH Before Reaction At EquilibriumExplanation / Answer
pH of deionized water = 7.0
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Strong acid HCl
With 1 ml of 3 M HCl in deionized water,
pH = -log[H+] = -log[3] = 0.48
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Strong base NaOH
With 1 ml of 3 M NaOH in deionized water,
pOH = -log[OH-] = -log[3] = 0.48
pH = 14 - pOH = 13.52
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pH of buffer solution
[AcOH] = 6 m x 4 ml/50 ml = 0.480 M
[NaOAc] = 3.3g/136.08 g/mol x 0.050 L = 0.485 M
pH = pKa + log(NaOAc/AcOH)
= 4.74 + log(0.485/0.480) = 4.744
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Buffer + HCl
[AcOH] = 0.480 M x 19 ml + 3 mmol = 12.12 mmol
[NaOAc] = 0.485 M x 19 ml - 3 mmol = 6.215 mmol
pH = pKa + log(NaOAc/AcOH)
= 4.74 + log(6.215/12.12) = 4.45
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Buffer + NaOH
[AcOH] = 0.480 M x 19 ml - 3 mmol = 6.215 mmol
[NaOAc] = 0.485 M x 19 ml + 3 mmol = 12.12 mmol
pH = pKa + log(NaOAc/AcOH)
= 4.74 + log(12.12/6.215) = 5.03
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