Open Question
Of ammonia, hydrazine, and hydroxylamine, which reacts to the greatest extent with the weak acid HNO₂? Consult Appendix C for equilibrium constants.
Ch.22 - The Main Group Elements
Chapter 22, Problem 166
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.
Verified step by step guidance1
Step 1: Determine the chemical reaction for the burning of white phosphorus (P4) in oxygen (O2) to form phosphorus pentoxide (P4O10). The balanced equation is: P4 + 5O2 -> P4O10.
Step 2: Calculate the moles of P4 burned using its molar mass. Use the stoichiometry of the reaction to find the moles of P4O10 produced.
Step 3: Dissolve the P4O10 in water to form phosphoric acid (H3PO4). The balanced equation is: P4O10 + 6H2O -> 4H3PO4. Calculate the concentration of H3PO4 in the 250.0 mL solution.
Step 4: For part (c), write the balanced equation for the reaction between H3PO4 and Ca(NO3)2 to form calcium phosphate precipitate: 2H3PO4 + 3Ca(NO3)2 -> Ca3(PO4)2 + 6HNO3. Calculate the mass of Ca3(PO4)2 precipitate using stoichiometry.
Step 5: For part (d), identify the gas produced when the remaining solution is treated with zinc. The reaction is: 2H3PO4 + 3Zn -> 3Zn3(PO4)2 + 3H2. Use the ideal gas law to calculate the volume of hydrogen gas (H2) collected at 20 °C and 742 mm Hg.
Related Practice
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.
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 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?