General Chemistry II: Chapter 17, Acid-Base Equilibria and Solubility Equilibria -Part I

Match each stage of a weak acid-strong base titration with the correct description of how to calculate [H₃O⁺] and/or pH. initial pH before equivalence point at equivalence point after equivalence point

-Calculate [H₃O⁺] using Ka and [HA] -[H₃O⁺] = Ka x [HA]/[A⁻] determined using reaction table -Calculate [OH⁻] using Kb and [A⁻]; [H₃O⁺] = Kw/[OH-] -pH depends on excess base added

A chemist titrates a 25.00-mL portion of 0.25 M HNO₃ with a 0.25 M solution of NaOH. Which of the following options correctly reflect the steps required to calculate the pH once 35.00 mL of NaOH has been added? Select all that apply.

-Moles of OH⁻ added = 8.75 x 10⁻³ -Moles of OH⁻ in excess = 2.5 x 10⁻³ -pH =12.62

Which of the following statements correctly describe the titration curve for the titration of a strong acid with a strong base? Select all that apply.

-The equivalence point is at a pH of 7.00 -The pH rise is very steep close to the equivalence point of the titration

A buffer used in food products is the benzoic acid/ benzoate buffer, which has a pKa = 4.19. If you need to maintain a pH of 3.50 using this buffer system, what concentration of benzoate ion would you need if you have 0.05 M benzoic acid?

0.01 M benzoate ion

25.0 mL of a 0.20 M solution of the weak acid CH₃COOH (K₈= 1.8 x 10⁻⁵) is titrated with 0.25 M NaOH. Place the steps required to calculate the pH at the equivalence point in the correct order, starting with the first step at the top of the list.

1) Moles CH₃COOH init = 25.0 mL x 1L/ 1000mL x 0.20 mol/ 1 L = 5.0 x 10⁻³ mol 2)Volume NaOH = 5.0 x 10⁻³ mol x 1 L/ 0.25 mol = 2.0 x 10⁻² L 3)[CH₃COO] = 5.0 x 10⁻³ mol/ 0.025 L + 0.020 L = 0.11 M 4) [OH⁻] = 1.0 x 10⁻¹⁴/ 1.8 x 10⁻⁵ x 0.11 = 7.8 x 10⁻⁶ M 5)pH = -log (1.0 x 10⁻¹⁴/ 7.8 x 10⁻⁶) = 8.89

Consider a buffer consisting of a weak acid (HA) and the corresponding conjugate base (A⁻). The buffer initially contains equal amounts of HA and A⁻. Match each picture to the correct representation of the buffer after the change indicated. Strong acid has been added. Strong base has been added.

A B

Which of the following options correctly describe how to calculate the pH at various stages during the titration of a strong acid against a strong base? Select all that apply.

At the equivalence point pH = 7.00 Initial ph = - log[HA]

Which of the following options represent heterogeneous equilibria? Select all apply.

BaSO₄ (s) ⇌ Ba²⁺ (aq) + SO²⁻4 (aq) 2H₂O (l) ⇌ 2H₂ (g) + O₂ (g) CaF₂ (s) ⇌ Ca²⁺ (aq) + 2 F (aq)

Which of the following conjugate acid-base pairs is the best choice to prepare a buffer of pH 3.50?

HCOOH/HCOONa (pKa of HCOOH = 3.74)

What is the equivalence point in an acid-base titration?

The point at which the acid has completely reacted with the base.

One type of acid-base buffer is composed of a weak _____, which will react with any added base, and its conjugate _____, which will react with any added acid.

acid base

Buffer _____ is a measure of the ability of a buffer to maintain the pH following the addition of strong acid or base.

capacity

Which of the following is the correct expression for the Henderson-Hasselbalch equation, which is used to calculate the pH of an acid-base buffer solution

pH = pKa + log([base]/[acid])

In a homogeneous solution equilibrium system, all the reactants and products are in the same ________.

physical state