Chemistry Chapter: Acid-Base Equilibria

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What is the equilibrium constant expression for the autoionization of water?

$K_w = [H_3O+][OH^-]$ (correct)

$K_w = [H_2O]/[H_3O+][OH^-]$

$K_w = [H_2O]^2/[H_3O+][OH^-]$

$K_w = [H_3O+][OH^-]/[H_2O]^2$

If the concentration of hydroxide ions ([OH-]) in a solution is 1.0 x 10^-10 M, what is the concentration of hydronium ions ([H3O+]) at 25°C?

1.0 x 10^-10 M

1.0 x 10^-14 M

1.0 x 10^-7 M

1.0 x 10^-4 M (correct)

A solution with a pH of 11 would best be described as what?

Strongly acidic

Strongly basic (correct)

Neutral

Slightly acidic

Which of the following statements accurately describes the autoionization of water?

Water molecules are amphoteric, meaning they can act as both an acid and a base, and they ionize to a very small extent. (A) Signup and view all the answers

What is the pOH of a solution with a hydronium ion concentration of 1.0 x 10^-3 M at 25°C?

11 (D) Signup and view all the answers

In the Henderson-Hasselbalch equation, what does the term 'pKa' represent?

The negative logarithm of the acid dissociation constant (Ka) (B) Signup and view all the answers

A buffer solution is prepared by mixing 0.10 M CH3COOH and 0.10 M CH3COONa. What is the pH of this buffer if the Ka for CH3COOH is 1.8 x 10^-5?

4.74 (C) Signup and view all the answers

Which of the following statements is TRUE about a buffer solution?

A buffer solution resists changes in pH when small amounts of strong acid or base are added. (D) Signup and view all the answers

What is the pH of a solution containing 0.10 M HCOOH and 0.10 M HCOO- if the pKa of HCOOH is 3.75?

3.75 (A) Signup and view all the answers

A buffer solution is prepared by mixing 0.20 M NH3 and 0.10 M NH4Cl. If the Kb for NH3 is 1.8 x 10-5, what is the pH of this buffer solution?

9.25 (C) Signup and view all the answers

What is the pH of a buffer solution consisting of 0.10 M H2CO3 and 0.10 M HCO3- if the Ka for H2CO3 is 4.3 x 10^-7?

6.37 (A) Signup and view all the answers

A buffer solution is prepared by mixing 0.25 M HF and 0.50 M NaF. What is the pH of this buffer if the Ka for HF is 7.2 x 10^-4?

3.14 (A) Signup and view all the answers

A solution containing 0.50 M CH3COOH and 0.50 M CH3COONa has a pH of 4.74 (pKa for CH3COOH is 4.74). If 0.01 mol of NaOH is added to 1 L of this buffer solution, what is the new pH of the solution?

4.77 (B) Signup and view all the answers

A student is performing an acid-base titration using a burette filled with a standardized sodium hydroxide solution. During the titration, they observe that the solution in the burette has air bubbles. Why is this a problem?

Air bubbles will cause an inaccurate measurement of the volume of sodium hydroxide solution used. (B) Signup and view all the answers

In a titration, a drop of phenolphthalein indicator is added to the analyte solution. What color change would the student expect to observe as the titration progresses?

The solution will change from colorless to pink. (D) Signup and view all the answers

A student carefully added 10.0 mL of hydrochloric acid to a clean Erlenmeyer flask. After the titrant was added, the student observed that the solution in the flask was still acidic. What should the student do next?

Continue adding sodium hydroxide solution until the pink color persists. (C) Signup and view all the answers

Why is it important to record the initial and final burette readings to the nearest 0.1mL during a titration?

To ensure that the volume of titrant used is accurately determined. (D) Signup and view all the answers

In the titration, a student records the initial burette reading as 10.0 mL and the final reading as 25.5 mL. What is the total volume of sodium hydroxide solution used in the titration?

15.5 mL (A) Signup and view all the answers

The normality of a solution is defined as the number of equivalents of solute per liter of solution. What is the normality of a 0.1 M solution of sodium hydroxide (NaOH)?

0.1 N (C) Signup and view all the answers

What is the primary purpose of using indicators like phenolphthalein in a titration?

To visually signal the endpoint of the titration. (A) Signup and view all the answers

A student is titrating a solution of hydrochloric acid (HCl) with a standard sodium hydroxide solution (NaOH). What is the significance of the equivalence point in this titration?

The equivalence point is the point at which the moles of HCl added are equal to the moles of NaOH added. (B) Signup and view all the answers

In the equilibrium reaction given, what would happen if the initial concentration of CH3COOH is increased to 0.20M, while the initial concentration of H3O+ is kept constant at 0.10M?

The equilibrium would shift to the right, favoring the formation of CH3COO- and H3O+. (B) Signup and view all the answers

Why is the Cl− ion considered a spectator ion in the reaction shown?

Because it does not participate in the proton transfer equilibrium of the reaction. (C) Signup and view all the answers

What is the significance of the statement 'x is very small' in the calculation of Ka?

It justifies ignoring the changes in concentration of CH3COOH and H3O+ at equilibrium, simplifying the calculation. (A) Signup and view all the answers

In the calculation of Ka, why is (0.10 − x) approximated to 0.10?

Because x is very small compared to 0.10, making the subtraction negligible. (B) Signup and view all the answers

A solution containing 0.20 M CH3COOH and 0.30 M CH3COONa acts as a buffer. Which of the following statements accurately describes the role of CH3COONa in this buffer?

CH3COONa provides the conjugate base component of the buffer. (C) Signup and view all the answers

What is the pH of a buffer solution after the addition of a small amount of strong base, like NaOH?

The pH will increase slightly, reflecting the reaction of the base with the weak acid in the buffer. (B) Signup and view all the answers

A buffer is defined as a solution that resists changes in pH. Why does a buffer solution resist such changes?

It contains a large concentration of a weak acid and its conjugate base, which can neutralize both added acids and bases. (C) Signup and view all the answers

Why is the addition of a small amount of acid or base to a buffer solution less likely to cause a significant change in pH, whereas the same amount of acid or base added to an unbuffered solution would cause a larger pH change?

The buffer solution contains a weak acid and its conjugate base, which can react with the added H+ or OH− ions, minimizing the changes in their concentrations. (D) Signup and view all the answers

What is the approximate hydroxide ion concentration, [OH-], in a 0.040 M solution of ammonia (NH3)?

3.6 x 10^-6 M (D) Signup and view all the answers

What is the value of [NH3] at equilibrium in a 0.040 M ammonia solution, considering the approximation method used in the content?

0.039 M (C) Signup and view all the answers

If the approximation method used in the content is deemed invalid for a 0.040 M ammonia solution, how would you proceed to find the equilibrium concentration of ammonia?

Use the quadratic formula to solve for x (A) Signup and view all the answers

Which of the following is NOT a valid assumption for the use of the approximation method in calculating equilibrium concentrations of a weak base like ammonia?

The equilibrium constant, Kb, is very small (D) Signup and view all the answers

What is the value of the pOH of a 0.040 M ammonia solution, assuming the approximation method is valid?

11.23 (A) Signup and view all the answers

What is the pH of a 0.040 M ammonia solution, given that the pOH is 11.23?

2.77 (B) Signup and view all the answers

What is the effect on the equilibrium position of the ammonia ionization reaction in water when the common ion (e.g., ammonium ion) is added?

The equilibrium will shift to the left, favoring the formation of ammonia (D) Signup and view all the answers

Which of the following statements correctly describes the common ion effect?

The common ion effect refers to the suppression of the ionization of a weak acid or base when a soluble salt containing the common ion is added to the solution (B) Signup and view all the answers

Why is a weak acid-base conjugate pair necessary for effective buffer solutions?

The presence of both acid and base components allows for the neutralization of both added H+ and OH- ions. (C) Signup and view all the answers

Explain why the equilibrium concentrations of acetic acid (CH3COOH) and acetate ions (CH3COO-) in a buffer solution are assumed to be similar to their starting concentrations.

The presence of both acetic acid and acetate ions inhibits the ionization of the weak acid and the hydrolysis of the acetate ion, preventing significant changes in their concentrations. (D) Signup and view all the answers

How does a buffer solution containing acetic acid and sodium acetate neutralize the addition of a base (OH-)?

The acetic acid donates protons to the hydroxide ions, neutralizing the base and forming water. (C) Signup and view all the answers

What is the main reason why the pH of blood is maintained at around 7.4?

The presence of proteins and other macromolecules in blood serve as buffers to resist changes in pH. (A) Signup and view all the answers

How does the Henderson-Hasselbalch equation relate to the pH of a buffer solution?

The equation provides a mathematical approximation of the buffer's pH, dependent on the ratio of the acidic and basic components. (A) Signup and view all the answers

Which of these statements accurately describes the principle underlying the functioning of a buffer solution?

Buffer solutions maintain a stable pH by reacting with added acids or bases, minimizing the change in pH. (B) Signup and view all the answers

Which of the following scenarios would NOT be a suitable application of a buffer solution?

Neutralizing excess stomach acid. (B) Signup and view all the answers

How does the concentration of the buffer components affect its buffering capacity?

Higher concentrations of buffer components lead to an increased capacity to resist pH changes. (B) Signup and view all the answers

Ionization of Water

The process where water molecules split into H3O+ and OH- ions.

Ion Product for Water (K_w)

The equilibrium constant for the ionization of water at 25°C, K_w = [H3O+][OH-].