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- Furoic acid (HC5H3O3) has a Ka value of 6.76 × 10^-4 at 25 _x001F_C. Calculate the pH at 25 _x001F_C of (a) a solution formed by adding 25.0 g of furoic acid and 30.0 g of sodium furoate (NaC5H3O3) to enough water to form 0.250 L of solution; (b) a solution formed by mixing 30.0 mL of 0.250 M HC5H3O3 and 20.0 mL of 0.22 M NaC5H3O3 and diluting the total volume to 125 mL; (c) a solution prepared by adding 50.0 mL of 1.65 M NaOH solution to 0.500 L of 0.0850 M HC5H3O3.
Problem 85
Problem 86
The acid–base indicator bromcresol green is a weak acid. The yellow acid and blue base forms of the indicator are present in equal concentrations in a solution when the pH is 4.68. What is the pKa for bromcresol green?
- Equal quantities of 0.010 M solutions of an acid HA and a base B are mixed. The pH of the resulting solution is 9.2. (a) Write the chemical equation and equilibrium-constant expression for the reaction between HA and B. (b) If Ka for HA is 8.0 × 10⁻⁵, what is the value of the equilibrium constant for the reaction between HA and B?
Problem 87
- Two buffers are prepared by adding an equal number of moles of formic acid (HCOOH) and sodium formate (HCOONa) to enough water to make 1.00 L of solution. Buffer A is prepared using 1.00 mol each of formic acid and sodium formate. Buffer B is prepared by using 0.010 mol of each. (a) Calculate the pH of each buffer. (b) Calculate the change in pH for each buffer upon the addition of 1.0 mL of 1.00 M HCl. (c) Calculate the change in pH for each buffer upon the addition of 10 mL of 1.00 M HCl.
Problem 88
Problem 88b
Two buffers are prepared by adding an equal number of moles of formic acid (HCOOH) and sodium formate (HCOONa) to enough water to make 1.00 L of solution. Buffer A is prepared using 1.00 mol each of formic acid and sodium formate. Buffer B is prepared by using 0.010 mol of each. (b) Which buffer will have the greater buffer capacity?
- A biochemist needs 750 mL of an acetic acid–sodium acetate buffer with pH 4.50. Solid sodium acetate (CH3COONa) and glacial acetic acid (CH3COOH) are available. Glacial acetic acid is 99% CH3COOH by mass and has a density of 1.05 g/mL. If the buffer is to be 0.15 M in CH3COOH, how many grams of CH3COONa and how many milliliters of glacial acetic acid must be used?
Problem 89
Problem 90a
A sample of 0.2140 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.0950 M NaOH. The acid required 30.0 mL of base to reach the equivalence point. (a) What is the molar mass of the acid?
Problem 91a
A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point. (a) What is the molar mass of the acid?
Problem 91b
A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point. (b) After 7.25 mL of base had been added in the titration, the pH was found to be 2.85. What is the Ka for the unknown acid?
- Mathematically prove that the pH at the halfway point of a titration of a weak acid with a strong base (where the volume of added base is half of that needed to reach the equivalence point) is equal to pKa for the acid.
Problem 92
- A weak monoprotic acid is titrated with 0.100 M NaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. After 25.0 mL of base is added, the pH of the solution is 3.62. Estimate the pKa of the weak acid.
Problem 93
- What is the pH of a solution made by mixing 0.30 mol NaOH, 0.25 mol Na2HPO4, and 0.20 mol H3PO4 with water and diluting to 1.00 L?
Problem 94
Problem 95
Suppose you want to do a physiological experiment that calls for a pH 6.50 buffer. You find that the organism with which you are working is not sensitive to the weak acid H2A 1Ka1 = 2 * 10-2; Ka2 = 5.0 * 10-72 or its sodium salts. You have available a 1.0 M solution of this acid and a 1.0 M solution of NaOH. How much of the NaOH solution should be added to 1.0 L of the acid to give a buffer at pH 6.50? (Ignore any volume change.)
- How many microliters of 1.000 M NaOH solution must be added to 25.00 mL of a 0.1000 M solution of lactic acid CH3CH(OH)COOH or HC3H5O3 to produce a buffer with pH = 3.75?
Problem 96
- Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (a) If the Ksp for PbCO3 is 7.4 * 10^-14, what is the molarity of Pb2+ in a saturated solution of lead(II) carbonate? (b) What is the concentration in ppb of Pb2+ ions in a saturated solution?
Problem 97
Problem 97d
Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (d) The EPA threshold for acceptable levels of lead ions in water is 15 ppb. Does a saturated solution of lead(II) carbonate produce a solution that exceeds the EPA limit?
Problem 98
For each pair of compounds, use Ksp values to determine which has the greater molar solubility: (a) CdS or CuS (b) PbCO3 or BaCrO4 (c) Ni(OH)2 or NiCO3 (d) AgI or Ag2SO4.
- The solubility of CaCO3 is pH dependent. (a) Calculate the molar solubility of CaCO3 given Ksp = 4.5 * 10^-92, neglecting the acid-base character of the carbonate ion. (c) If we assume that the only sources of Ca2+, HCO3-, and OH- ions are from the dissolution of CaCO3, what is the molar solubility of CaCO3 using the equilibrium expression from part (b)?
Problem 99
Problem 99b
The solubility of CaCO3 is pH dependent. (b) Use the Kb expression for the CO32- ion to determine the equilibrium constant for the reaction CaCO3(s) + H2O(l) ⇌ Ca2+(aq) + HCO3-(aq) + OH-(aq)
Problem 100a
Tooth enamel is composed of hydroxyapatite, whose simplest formula is Ca51PO423OH, and whose corresponding Ksp = 6.8 * 10-27. As discussed in the Chemistry and Life box on page 746, fluoride in fluorinated water or in toothpaste reacts with hydroxyapatite to form fluoroapatite, Ca51PO423F, whose Ksp = 1.0 * 10-60. (a) Write the expression for the solubility-constant for hydroxyapatite and for fluoroapatite.
- What is the pH of a 1 * 10^-3 M solution of Na3PO4? You can ignore the formation of H2PO4- and H3PO4^2-.
Problem 101
Problem 102
Calculate the solubility of Mg1OH22 in 0.50 M NH4Cl.
Problem 103
The solubility-product constant for barium permanganate, Ba1MnO422, is 2.5 * 10-10. Assume that solid Ba1MnO422 is in equilibrium with a solution of KMnO4. What concentration of KMnO4 is required to establish a concentration of 2.0 * 10-8 M for the Ba2 + ion in solution?
- A solid sample of Fe1OH23 is added to 0.500 L of 0.250 M aqueous H2SO4. The solution that remains is still acidic. It is then titrated with 0.500 M NaOH solution, and it takes 12.5 mL of the NaOH solution to reach the equivalence point. What mass of Fe1OH23 was added to the H2SO4 solution?
Problem 104
Problem 105
The solubility product constants of PbSO4 and SrSO4 are 6.3 * 10-7 and 3.2 * 10-7, respectively. What are the values of 3SO4 2 - 4, 3Pb2 + 4, and 3Sr2 + 4 in a solution at equilibrium with both substances?
- What pH is needed for a buffer to achieve a Mg2+ concentration of 3.0 × 10^-2 M in equilibrium with solid magnesium oxalate?
Problem 106
- The value of Ksp for Mg₃₁(AsO₄)₂₂ is 2.1 * 10⁻²⁰. The AsO₄³⁻ ion is derived from the weak acid H₃AsO₄ with pKa₁ = 2.22, pKa₂ = 6.98, pKa₃ = 11.502. (b) Calculate the pH of a saturated solution of Mg₃₁(AsO₄)₂₂ in water.
Problem 107
Problem 108
The solubility product for Zn1OH22 is 3.0 * 10-16. The formation constant for the hydroxo complex, Zn1OH242 - , is 4.6 * 1017. What concentration of OH- is required to dissolve 0.015 mol of Zn1OH22 in a liter of solution?
Problem 109a
The value of Ksp for Cd(OH)2 is 2.5 × 10-14. (a) What is the molar solubility of Cd(OH)2?
Problem 109b
The value of Ksp for Cd(OH)2 is 2.5 × 10–14. (b) The solubility of Cd(OH)2 can be increased through formation of the complex ion CdBr42- (Kf = 5 × 103). If solid Cd(OH)2 is added to a NaBr solution, what is the initial concentration of NaBr needed to increase the molar solubility of Cd(OH)2 to 1.0 × 10-3 mol/L?