AP Chem Unit 08 Day 05 Practice

Which of the following combinations of equimolar substances would NOT make a buffer?

• HNO₂ and NaNO₂

• HCl and NaCl

• NH₄Cl and NH₃

• HCO₂H and NaCO₂H

When creating an effective buffer with a large capacity, what is the best ratio of weak base to conjugate acid?

• 1 : 1

• 10 : 1

• 1 : 10

• 0.1 : 1

A buffer solution is prepared by mixing equal volumes of 0.10M formic acid, HCOOH, and 0.10M sodium formate, NaCOOH. Which of the following equations represents the reaction that best helps to explain why adding a few drops of 1.0M NaOH(aq) does not significantly change the pH of the solution?

•  H₃O⁺(aq) + COOH^─(aq) → HCOOH (aq) + H₂O(l)

•  H₃O⁺(aq) + OH^─(aq) → H₂O(l)

•  HCOOH (aq) + H₂O(l) ⇄ H₃O⁺(aq) + COOH^─(aq)

• HCOOH (aq) + OH^─(aq) → COOH^─(aq) + H₂O(l)

A 1.0L buffer is prepared by that is 0.20M HNO₂ and 0.50M KNO₂. Which of the following actions would overcome the buffer capacity?

• Adding 0.40 mol of HNO₂

• Adding 0.40 mol of KNO₂

• Adding 0.40 mol of HBr

• Adding 0.40 mol of KOH

To prepare the following solutions, 1.00 mole of each substance in the pair is dissolved in water to make 1.00L of total solution. Which of the following pairs will have the highest

pH?

• NH₄Cl and NH₃

• Ca(OH)₂ and NH₃

• HI and KI

• HF and KF

A student wants to make a buffer with a pH closest to 5.0. Use the weak acid and weak base

systems above to determine the best conjugate pair to make this buffer.

• HCHO₂

  and

  CHO₂^─

• HClO

  and

  ClO^─

• CH₃NH₂

  and

  CH₃NH₃⁺

• C₅H₅N

  and

  C₅H₅NH⁺

A buffer has a pH of 4.85 and contains formic acid, HCOOH, and potassium formate, KCOOH. What can you conclude about the concentrations of the components of the buffer? The Ka of formic acid is 1.8 x 10^-4.

• formic acid > potassium formate

• formic acid = potassium formate

• formic acid < potassium formate

• A buffer cannot be created from formic acid and postassium formate.

A student prepares 1.0L of an ideal buffer using 0.1M hydrofluoric acid and 0.1M sodium fluoride. The pH of this ideal buffer is 3.14. The student then prepares 1.0L of an ideal buffer using 0.2M hydrofluoric acid and 0.2M sodium fluoride. What is the pH of the second buffer?

• pH = 3.14; The ratio of

  [𝐴𝑐𝑖𝑑]/[𝐵𝑎𝑠𝑒]

  remains unchanged.

• pH > 3.14; There is a greater amount of each component and the buffer capacity is

  increased.

• pH < 3.14; There is a greater amount of each component and the buffer capacity is

  increased.

• pH cannot be determined; Greater amounts of each component will change the value of

  the acid-dissociation constant, Ka.

A student is provided with 1.0L of a 1.0M acetic acid, HC₂H₃O₂, solution and is tasked with preparing an ideal buffer. Unfortunately, the student does not have any salts that contain the acetate ion, its conjugate base. Which of the following could the student add to the acetic acid solution still prepare the buffer?

• Add 1.0 L of a 1.0M HCl solution.

• Add 1.0L of a 1.0M NaOH solution.

• Add 0.50L of a 1.0M HCl solution.

• Add 0.50L of a 1.0M NaOH solution.

Using the table of Ka values provided above, which of the following mixtures would result in a buffer with a pH between 9 and 13?

• A mixture of 50.mL of 1.0M NaIO and 25mL of 1.0M HCl.

• A mixture of 50.mL of 1.0M HClO₂ and 50mL of 1.0M NaClO₂.

• A mixture of 50.mL of 1.0M HIO and 50.mL of 1.0M HCl.

• A mixture of 50.mL of 1.0M HIO and 25 mL of 1.0M HCl.