3. Nitrous acid, HNO2, is a weak acid that ionizes according to Equation 1. Equation 1: HNO2(aq) + H — Acid-Base Equilibria, Titration, Thermodynamics Chemistry Question
Problem Context
3. Nitrous acid, HNO2, is a weak acid that ionizes according to Equation 1.
Equation 1: HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq) Ka = 5.6 × 10^-4 at 298 K
Identify a conjugate acid-base pair in the equation. Be sure to clearly label which is the acid and which is the base.
A solution of HNO2(aq) with an initial concentration of 0.125 M has a pH of 2.09.
i. Calculate the value of [H3O+] in the solution. Show the work that leads to your answer.
ii. Calculate [HNO2] at equilibrium. Show the work that leads to your answer.
In an experiment, the solution of 0.125 M HNO2(aq) is heated to 333 K. The new equilibrium concentrations are determined to be [HNO2] = 0.114 M, [NO2-] = 0.0109 M, and [H3O+] = 0.0109 M.
i. Calculate the value of Ka for HNO2 at 333 K. Show the work that leads to your answer.
ii. Is the reaction represented by Equation 1 endothermic or exothermic? Justify your answer by comparing Ka values at 298 K and 333 K.
The following information applies to parts D, E, and F.
In a second experiment, a student is given a bottle containing HNO2 with an unknown molarity. To determine the concentration of the HNO2(aq) in the bottle, the student titrates 35.0 mL of the HNO2(aq) with 0.16 M NaOH(aq) at 298 K, which reacts according to Equation 2.
Equation 2: HNO2(aq) + OH-(aq) → NO2-(aq) + H2O(l)
The results of the titration are summarized in Figure 1.
Using Figure 1, identify the pH at the equivalence point.
Using Figure 1, calculate the molarity of HNO2(aq) in the bottle. Show the work that leads to your answer.
Draw an X on Figure 1 to represent a point in the titration where [HNO2] = [NO2-] in the reaction mixture.
Equilibrium constants at 298 K are shown in Table 1 for the acid ionization reaction represented by Equation 1, Ka; the autoionization of water, Kw; and the neutralization reaction represented by Equation 2, K2.
Calculate the value of K2 for Equation 2 at 298 K. Show the work that leads to your answer.
The student decides to repeat the experiment, this time using an indicator, and has access to the indicators in Table 2.
The student conducts a second titration by adding two drops of methyl orange indicator to 35.0 mL of the HNO2(aq) solution and titrating the solution with 0.16 M NaOH(aq) until a color change from red to yellow occurs.
The student claims that methyl orange was the best choice for the indicator. Do you agree or disagree? Justify your answer.