Questions and Answers
Which of the following are valid ways to make an ammonia/ammonium buffer for use in the laboratory?
If you have 925 mL of a 0.818 M acetic acid solution, how many milliliters of a 2.79 M KOH solution do you need to add to make a buffer of pH 6.24?
262.5 mL
How does a buffer resist change in pH upon addition of a strong acid?
The strong acid reacts with the weak base in the buffer to form a weak acid.
Which acid (and its conjugate base) would be the best buffer at pH = 4.7?
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If a buffer solution is 0.110 M in a weak acid (Ka = 8.1 × 10^-5) and 0.510 M in its conjugate base, what is the pH?
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What is the change in pH when 7.00 mL of 0.100 M HCl is added to a buffer solution that is 0.100 M in NH3 and 0.100 M in NH4Cl?
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What is the change in pH when 7.00 mL of 0.100 M NaOH is added to the same buffer solution?
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Classify each titration curve as representing which type of titration?
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Determine the relative pH at these points for the titration of 35.0 mL of 0.350 M NH3 with 0.500 M HCl.
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Calculate the pH for the following cases in the titration of 50.0 mL of 0.200 M HClO with 0.200 M KOH. What is the pH after 0 mL, 25 mL, 40 mL, 50 mL, and 60 mL of KOH is added?
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Classify the following substances as Lewis acids or Lewis bases.
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Identify the Lewis acid and Lewis base in the following reactions.
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Express Ksp in terms of molar solubility, x, for a salt with the formula AB.
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What is the Ksp of a salt AB2, knowing that only 0.0640 mol is soluble in 1.00 L of water?
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What is the molar solubility of PbBr2 in pure water given Ksp as 6.60 × 10^-6?
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What is the Ksp of a generic metal hydroxide M(OH)2 at 22 °C given that the resulting equilibrium solution has a pH of 10.32?
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Study Notes
Ammonia and Acetate Buffers
- Ammonia/ammonium buffer can be created by mixing 1 M NH3 with half as much 1 M HCl, or by mixing equal volumes of 1 M NH3 and 1 M NH4Cl.
- To prepare an acetate buffer at pH 6.24, mix 262.5 mL of 2.79 M KOH with 925 mL of 0.818 M acetic acid, using the Henderson-Hasselbalch equation for calculations.
Buffer Resistance to pH Change
- A buffer resists pH changes when a strong acid is added, as the acid reacts with the weak base in the buffer, generating a weak acid and minimizing H⁺ ion concentration.
Buffer Selection
- Acetic acid (Ka = 1.8 × 10^-5) is a suitable buffer at pH 4.7, with its pKa calculated to be approximately 4.744, indicating its effectiveness within a pH range of 3.744 to 5.744.
pH Calculation in Buffer Solutions
- For a buffer with 0.110 M weak acid and 0.510 M conjugate base, the pH is approximately 4.8.
- Determine pH changes when subjected to HCl or NaOH in a buffer solution; adding 7.00 mL of 0.100 M HCl changes pH by -0.06, while adding 7.00 mL of 0.100 M NaOH results in a +0.06 change.
Titration Curves
- Various titration curves indicate that before adding HCl to NH3 solution, pH > 7, after adding 24.5 mL, pH < 7, and after 39.5 mL, pH remains < 7.
Titration Outcomes
- In the titration of 50.0 mL of 0.200 M HClO with 0.200 M KOH:
- pH before KOH addition is 4.11,
- after 25.0 mL, pH rises to 7.52,
- after 40.0 mL, it reaches 8.12,
- at 50.0 mL, it is 10.26,
- and after adding 60.0 mL, it climbs to 12.26.
Lewis Acids and Bases
- Lewis acids include SO3, CO^3+, BeCl2; Lewis bases include S^2-, OF2.
- Identifying Lewis acids and bases in reactions is crucial for understanding chemical interactions.
Solubility Product (Ksp)
- Ksp expressions based on molar solubility x are as follows:
- AB: Ksp = x²
- AB2: Ksp = 4x³
- AB3: Ksp = 27x⁴
- A3B2: Ksp = 108x⁵.
Specific Ksp Calculations
- For the salt AB2, Ksp = 1.05 × 10^-3, calculated using molar solubility.
- The Ksp for PbBr2, given as 6.60 × 10^-6, leads to different molar solubilities when conditioned with KBr or Pb(NO3)2.
Ksp Determination from pH
- For M(OH)2 at pH 10.32, the Ksp is 4.54 × 10^-12, calculated from the relationship between hydroxide ion concentration and the solubility of the metal ion.
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Description
Test your understanding of ammonia and acetate buffer systems. This quiz covers buffer preparation, resistance to pH changes, and pH calculations using the Henderson-Hasselbalch equation. Assess how different acids and bases affect buffer solutions.
