
Concept explainers
For the titration of 10.0 mL of 0.15 M acetic acid with 0.10 M sodium hydroxide, determine the pH when (a) 10.0 mL of base has been added, (b) 15 .0 mL of base has been added, and (c) 20.0 mL of base has been added.
(a)

Interpretation:
The pH of titration NaOH Vs CH3COOH on adding various amount of sodium hydroxide has to be calculated.
Concept introduction:
- pH is the logarithm of the reciprocal of the concentration of H3O+ in a solution.
- The point at which amount of standard solution and analyte becomes equal and neutralisation happens in titration is called equivalence point.
- pH = pKa + log[conjugate base][acid] is Henderson-Hasselbalch equation.
- Buffer solution is defined as a solution that oppose changes in pH while adding little amount of either an acid or a base.
- Buffer solution is a combination of a weak acid and its conjugate base or a weak base and its conjugate acid.
To calculate: The pH when 10mL NaOH is added.
Answer to Problem 4PPA
pH = 5.04
Explanation of Solution
The pH of buffer solution when 10mL NaOH is added is calculated below.
The number of moles of acetic acid is(0.15 mmol/mL)(10.0 mL) = 1.50 mmol of acetic acidThe number of moles of NaOH is(0.10 mmol/mL)(10.0 mL) = 1.00 mmol of NaOH
CH3COOH(aq) +OH-(aq) ⇄→ H2O(l) + CH3COO-(aq) Initial concentration(M): 1.50mmol 0 Change in concentration (M): -1.00mmol +1.00mmol Equilibrium concentration (M): 0.50mmol 1.00mmol pH = pKa + log[conjugate base][acid] pH = 4.74 + log1.000.50 pH = 4.74 + 0.30 pH = 5.04
(b)

Interpretation:
The pH of titration NaOH Vs CH3COOH on adding various amount of sodium hydroxide has to be calculated.
Concept introduction:
- pH is the logarithm of the reciprocal of the concentration of H3O+ in a solution.
- The point at which amount of standard solution and analyte becomes equal and neutralisation happens in titration is called equivalence point.
- pH = pKa + log[conjugate base][acid] is Henderson-Hasselbalch equation.
- Buffer solution is defined as a solution that oppose changes in pH while adding little amount of either an acid or a base.
- Buffer solution is a combination of a weak acid and its conjugate base or a weak base and its conjugate acid.
To calculate: The pH when 15mL NaOH is added that is at equivalence point.
Answer to Problem 4PPA
pH = 8.87
Explanation of Solution
The pH of buffer solution when 15mL NaOH is added is calculated below.
The number of moles of acetic acid is(0.15 mmol/mL)(10.0 mL) = 1.50 mmol of acetic acidThe number of moles of NaOH is(0.10 mmol/mL)(15.0 mL) = 1.50 mmol of NaOH
At equivalence point, the total volume of solution is
10.0mL(acetic acid) + 15.0 mL(base) = 25.0 mL
At equivalence point, the concentration of acetate ion is
1.50mmol acetate ion15.0mL = 0.1M
CH3COO-(aq) +H2O(l) ⇄→ OH-(aq) + CH3COO-(aq) Initial concentration(M): 0.1 0 0 Change in concentration (M): -x -x +x Equilibrium concentration (M): 0.1-x x x Kb value for acetate ion is 5.6 × 10-10 Kb = [OH-][CH3COOH][CH3COO-] 5.6 × 10-10 = x2(0.1-x)x is very small and neglect it, x2 = 5.6 × 10-11 x = 7.48 × 10-6M x = [OH-] = 7.48 × 10-6M pOH = -log[OH-] = -log(7.48 × 10-6) pOH = 5.13 pH = 14.00 - 5.13 = 8.87
(c)

Interpretation:
The pH of titration NaOH Vs CH3COOH on adding various amount of sodium hydroxide has to be calculated.
Concept introduction:
- pH is the logarithm of the reciprocal of the concentration of H3O+ in a solution.
- The point at which amount of standard solution and analyte becomes equal and neutralisation happens in titration is called equivalence point.
- pH = pKa + log[conjugate base][acid] is Henderson-Hasselbalch equation.
- Buffer solution is defined as a solution that oppose changes in pH while adding little amount of either an acid or a base.
- Buffer solution is a combination of a weak acid and its conjugate base or a weak base and its conjugate acid.
To calculate: The pH when 20mL NaOH is added that is beyond equivalence point.
Answer to Problem 4PPA
pH = 12.82
Explanation of Solution
The pH of buffer solution when 20mL NaOH is added is calculated below.
The number of moles of NaOH is(0.10 mmol/mL)(20.0 mL) = 2.0 mmol of NaOHTotal volume of solution is 10.0 + 20.0 = 35.0 mL
The concentration of sodium hydroxide is
[OH-] = 2.00 mmol/30.0 mL = 0.0666 MpOH = -log (0.0666) = 1.24pH = 14.000 - 1.176 = 12.82
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Chapter 17 Solutions
Chemistry: Atoms First
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