Open Question
Write balanced equations for the reactions of (a) H3PO4 and (b) B1OH23 with water. Classify each acid as a Brønsted–Lowry acid or a Lewis acid.
Ch.22 - The Main Group Elements
Chapter 22, Problem 167
A 500.0 mL sample of an equilibrium mixture of gaseous N2O4 and NO2 at 25 °C and 753 mm Hg pressure was allowed to react with enough water to make 250.0 mL of solution at 25 °C. You may assume that all the dissolved N2O4 is converted to NO2, which disproportionates in water, yielding a solution of nitrous acid and nitric acid. Assume further that the disproportionation reaction goes to completion and that none of the nitrous acid disproportionates. The equilibrium constant Kp for the reaction N2O4(g) ⇌ 2 NO2(g) is 0.113 at 25 °C. Ka for HNO2 is 4.5 * 10^-4 at 25 °C. (a) Write a balanced equation for the disproportionation reaction. (b) What is the molar concentration of NO2-, and what is the pH of the solution? (c) What is the osmotic pressure of the solution in atmospheres? (d) How many grams of lime (CaO) would be needed to neutralize the solution?
Verified step by step guidance1
Step 1: Write the balanced chemical equation for the disproportionation reaction of NO2 in water. NO2 reacts with water to form nitrous acid (HNO2) and nitric acid (HNO3). The balanced equation is: 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(aq).
Step 2: Calculate the initial moles of N2O4 and NO2 using the ideal gas law. Use the given pressure (753 mm Hg), volume (500.0 mL), and temperature (25 °C) to find the total moles of gas. Then, use the equilibrium constant Kp to find the equilibrium concentrations of N2O4 and NO2.
Step 3: Determine the moles of NO2 that dissolve in water and undergo disproportionation. Since the reaction goes to completion, all NO2 is converted to HNO2 and HNO3. Calculate the moles of each acid formed using stoichiometry from the balanced equation.
Step 4: Calculate the molar concentration of NO2- in the solution. Use the dissociation constant (Ka) for HNO2 to find the concentration of NO2- ions in the solution. Set up an equilibrium expression for the dissociation of HNO2 and solve for the concentration of NO2-.
Step 5: Calculate the pH of the solution using the concentration of H+ ions from the dissociation of HNO2 and HNO3. Use the formula pH = -log[H+]. Then, calculate the osmotic pressure using the formula π = iMRT, where i is the van't Hoff factor, M is the molarity, R is the gas constant, and T is the temperature in Kelvin. Finally, determine the grams of lime (CaO) needed to neutralize the solution by calculating the moles of H+ and using stoichiometry with the reaction CaO + 2 H+ → Ca2+ + H2O.
Related Practice
Open Question
Consider phosphorous acid, a polyprotic acid with the formula H3PO3. (a) Draw two plausible structures for H3PO3. For each one, predict the shape of the pH titration curve for the titration of H3PO3 (Ka1 = 1.0 * 10^-2) with aqueous NaOH. (b) For the structure with the H atoms in two different environments, calculate the pH at the first and second equivalence points, assuming that 30.00 mL of 0.1240 M H3PO3 (Ka2 = 2.6 * 10^-7) is titrated with 0.1000 M NaOH.
Open Question
A 5.00 g quantity of white phosphorus was burned in an excess of oxygen, and the product was dissolved in enough water to make 250.0 mL of solution. (b) What is the pH of the solution? (c) When the solution was treated with an excess of aqueous Ca(NO3)2, a white precipitate was obtained. Write a balanced equation for the reaction and calculate the mass of the precipitate in grams. (d) The precipitate in part (c) was removed, and the solution that remained was treated with an excess of zinc, yielding a colorless gas that was collected at 20 °C and 742 mm Hg. Identify the gas, and determine its volume.