Ch.16 - Aqueous Equilibria: Acids & Bases
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- Calculate the pH and the percent dissociation of the hydrated cation in the following solutions. See Appendix C for the value of the equilibrium constant. (a) 0.010 M Cr1NO323
Problem 135
- Baking powder contains baking soda, NaHCO3, and an acidic substance such as sodium alum, NaAl(SO4)2 ~ 12 H2O. These components react in an aqueous medium to produce CO2 gas, which “raises” the dough. Write a balanced net ionic equation for the reaction.
Problem 136
- Arrange the following substances in order of increasing H3O+ concentration for a 0.10 M solution of each. (a) Zn(NO3)2 (b) Na2O (c) NaOCl (d) NaClO4 (e) HClO4
Problem 137
- For each of the Lewis acid–base reactions in Problem 16.139, draw electron-dot structures for the reactants and products, and use the curved arrow notation to represent the donation of a lone pair of electrons from the Lewis base to the Lewis acid.
Problem 141
- Classify each of the following as a Lewis acid or a Lewis base. (e) OH-
Problem 142
- Which would you expect to be the stronger Lewis acid in each of the following pairs? Explain. (a) BF3 or BH3
Problem 143
- Calculate the pH and the concentrations of all species present (H3O+ , F-, HF, Cl-, and OH-) in a solution that contains 0.10 M HF 1Ka = 3.5 * 10-42 and 0.10 M HCl.
Problem 146
- When NO2 is bubbled into water, it is completely converted to HNO3 and HNO2: 2 NO21g2 + H2O1l2S HNO31aq2 + HNO21aq2 Calculate the pH and the concentrations of all species present (H3O+ , OH-, HNO2, NO2 -, and NO3 -) in a solution prepared by dissolving 0.0500 mol of NO2 in 1.00 L of water. Ka for HNO2 is 4.5 * 10-4.
Problem 147
- Normal rain has a pH of 5.6 due to dissolved atmospheric carbon dioxide at a current level of 400 ppm. Various models predict that burning fossil fuels will increase the atmospheric CO2 concentration to between 500 and 1000 ppm by the year 2100. (a) Calculate the pH of rain in a scenario where the CO2 concentration is 750 ppm. CO2 reacts with water to produce carbonic acid according to the equation: CO2(aq) + H2O(l) ⇌ H2CO3(aq). Assume all the dissolved CO2 is converted to H2CO3. Acid dissociation constants for H2CO3 are Ka1 = 4.3 * 10^-7; Ka2 = 5.6 * 10^-11. (Worked Example 16.11 is a model for this calculation.) (b) Will rising CO2 levels affect the acidity of rainfall?
Problem 148
- Sulfur dioxide is quite soluble in water: SO2(g) + H2O(l) ⇌ H2SO3(aq), K = 1.33. The H2SO3 produced is a weak diprotic acid (Ka1 = 1.5 * 10^-2; Ka2 = 6.3 * 10^-8). Calculate the pH and the concentrations of H2SO3, HSO3-, and SO3^2- in a solution prepared by continuously bubbling SO2 at a pressure of 1.00 atm into pure water.
Problem 149
- Acid and base behavior can be observed in solvents other than water. One commonly used solvent is dimethyl sulfoxide (DMSO), which can be treated as a monoprotic acid 'HSol.' Just as water can behave either as an acid or a base, so HSol can behave either as a Brønsted–Lowry acid or base. (b) The weak acid HCN has an acid dissociation constant Ka = 1.3 * 10-13 in the solvent HSol. If 0.010 mol of NaCN is dissolved in 1.00 L of HSol, what is the equilibrium concentration of H2Sol + ?
Problem 151
- A 7.0 mass % solution of H3PO4 in water has a density of 1.0353 g/mL. Calculate the pH and the molar concentrations of all species present (H3PO4, H2PO4-, PO43-, H3O+ , and OH-) in the solution. Values of equilibrium constants are listed in Appendix C.
Problem 152
- In the case of very weak acids, 3H3O+ 4 from the dissociation of water is significant compared with 3H3O+ 4 from the dissociation of the weak acid. The sugar substitute saccharin 1C7H5NO3S2, for example, is a very weak acid having Ka = 2.1 * 10-12 and a solubility in water of 348 mg/100 mL. Calculate 3H3O+ 4 in a saturated solution of saccharin. (Hint: Equilibrium equations for the dissociation of saccharin and water must be solved simultaneously.)
Problem 153
- In aqueous solution, sodium acetate behaves as a strong electrolyte, yielding Na+ cations and CH3CO2 - anions. A particular solution of sodium acetate has a pH of 9.07 and a density of 1.0085 g/mL. What is the molality of this solution, and what is its freezing point?
Problem 154
Problem 155a
During a certain time period, 4.0 million tons of SO2 were released into the atmosphere and subsequently oxidized to SO3. As explained in the Inquiry, the acid rain produced when the SO3 dissolves in water can damage marble statues: CaCO3(s) + H2SO4(aq) → CaSO4(aq) + CO2(g) + H2O(l) (a) How many 500 pound marble statues could be damaged by the acid rain? (Assume that the statues are pure CaCO3 and that a statue is damaged when 3.0% of its mass is dissolved.)
- We’ve said that alkali metal cations do not react appreciably with water to produce H3O+ ions, but in fact, all cations are acidic to some extent. The most acidic alkali metal cation is the smallest one, Li+, which has Ka = 2.5 * 10^-14 for the reaction: Li(H2O)4+ (aq) + H2O (l) ⇌ H3O+ (aq) + Li(H2O)3(OH) (aq). This reaction and the dissociation of water must be considered simultaneously in calculating the pH of Li+ solutions, which nevertheless have pH ≈ 7. Check this by calculating the pH of a 0.10 M LiCl solution.
Problem 157
Problem 158a
A 1.000 L sample of HF gas at 20.0 °C and 0.601 atm pressure was dissolved in enough water to make 50.0 mL of hydrofluoric acid. (a) What is the pH of the solution?
Problem 158b
A 1.000 L sample of HF gas at 20.0 °C and 0.601 atm pressure was dissolved in enough water to make 50.0 mL of hydrofluoric acid. (b) To what volume must you dilute the solution to triple the percent dissociation?
- A 200.0 mL sample of 0.350 M acetic acid (CH3CO2H) was allowed to react with 2.000 L of gaseous ammonia at 25 °C and a pressure of 650.8 mm Hg. Assuming no change in the volume of the solution, calculate the pH and the equilibrium concentrations of all species present (CH3CO2H, CH3CO2-, NH3, NH4+, H3O+, and OH-). Values of equilibrium constants are listed in Appendix C.
Problem 159
- You may have been told not to mix bleach and ammonia. The reason is that bleach (sodium hypochlorite) reacts with ammonia to produce toxic chloramines, such as NH2Cl. For example, in basic solution: OCl-1aq2 + NH31aq2S OH-1aq2 + NH2Cl1aq2 (b) The following mechanism has been proposed for this reaction in basic solution: H2O + OCl-HOCl + OH- Fast, equilibrium constantK1 HOCl + NH3 S H2O + NH2Cl Slow, rate constantk2 Assuming that the first step is in equilibrium and the second step is rate-determining, calculate the value of the rate constant k2 for the second step. Ka for HOCl is 3.5 * 10-8.
Problem 160