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Ch.16 - Aqueous Equilibria: Acids & Bases
All textbooksMcMurry 8th EditionCh.16 - Aqueous Equilibria: Acids & BasesProblem 159
Chapter 16, Problem 159

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.

Verified step by step guidance
1
Step 1: Calculate the initial moles of acetic acid (CH3CO2H) using its concentration and volume. Use the formula: \( \text{moles} = \text{concentration} \times \text{volume} \).
Step 2: Determine the moles of gaseous ammonia (NH3) using the ideal gas law, \( PV = nRT \), where \( P \) is the pressure, \( V \) is the volume, \( R \) is the ideal gas constant, and \( T \) is the temperature in Kelvin.
Step 3: Write the balanced chemical equation for the reaction between acetic acid and ammonia, and use stoichiometry to find the limiting reactant and the moles of products formed.
Step 4: Use the equilibrium constant expressions for the dissociation of acetic acid (\( K_a \)) and the ionization of ammonia (\( K_b \)) to set up equations for the equilibrium concentrations of all species.
Step 5: Solve the equilibrium expressions simultaneously to find the concentrations of \( \text{CH}_3\text{CO}_2^- \), \( \text{NH}_4^+ \), \( \text{H}_3\text{O}^+ \), and \( \text{OH}^- \). Use these to calculate the pH of the solution.
Related Practice
Open Question
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.
Textbook Question

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?

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Textbook Question

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?

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Textbook Question
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.
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