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Questions and Answers
Which of the following are valid ways to make an ammonia/ammonium buffer for use in the laboratory?
Which of the following are valid ways to make an ammonia/ammonium buffer for use in the laboratory?
- Mix 0.5 M NH3 with 0.5 M HCl
- Mix some volume of 1 M NH3 with half as much 1 M HCl (correct)
- Mix equal volumes of 1 M NH3 and 1 M NH4 (correct)
- Mix 1 M NH4 with 1 M HCl
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?
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?
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?
Which acid (and its conjugate base) would be the best buffer at pH = 4.7?
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?
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?
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?
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?
What is the change in pH when 7.00 mL of 0.100 M NaOH is added to the same buffer solution?
What is the change in pH when 7.00 mL of 0.100 M NaOH is added to the same buffer solution?
Classify each titration curve as representing which type of titration?
Classify each titration curve as representing which type of titration?
Determine the relative pH at these points for the titration of 35.0 mL of 0.350 M NH3 with 0.500 M HCl.
Determine the relative pH at these points for the titration of 35.0 mL of 0.350 M NH3 with 0.500 M HCl.
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?
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?
Classify the following substances as Lewis acids or Lewis bases.
Classify the following substances as Lewis acids or Lewis bases.
Identify the Lewis acid and Lewis base in the following reactions.
Identify the Lewis acid and Lewis base in the following reactions.
Express Ksp in terms of molar solubility, x, for a salt with the formula AB.
Express Ksp in terms of molar solubility, x, for a salt with the formula AB.
What is the Ksp of a salt AB2, knowing that only 0.0640 mol is soluble in 1.00 L of water?
What is the Ksp of a salt AB2, knowing that only 0.0640 mol is soluble in 1.00 L of water?
What is the molar solubility of PbBr2 in pure water given Ksp as 6.60 × 10^-6?
What is the molar solubility of PbBr2 in pure water given Ksp as 6.60 × 10^-6?
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?
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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