We Suffers with Buffers

Which of the following is the correct equilibrium expression for the hydrolysis of CO₃^2– ?

CO₃^2- + H₂O ⇌ HCO₃^- + OH^-

• a

• b

• c

• d

What does a buffer do?

• Keeps the pH of a solution relatively constant

• Keeps the salt concentration of a solution relatively constant

• Keeps the cation concentration constant

• Keeps the anion concentration constant

What substances are present in a buffer?

• A weak base or acid and its salt

• A hydrolyzing salt only

• A weak base or acid only

• A salt only

The addition of hydrofluoric acid and __________ to water produces a buffer solution.

• HCl

• NaNO₃

• NaF

• NaCl

Which of the following reactions shows what happens when potassium hydroxide is added to an ammonium ion/ammonia buffer?

• OH^- + NH₃ ⇌ NH₃OH

• K⁺ + NH₃⇌ KNH₃

• K⁺ + NH₄⁺ ⇌ NH₄K

• OH^- + NH₄⁺ ⇌ NH₃ + H₂O

HSO₄⁻ + H₂O ⇌ H₃O⁺ + SO₄²⁻

In the equilibrium represented above, the species that act as bases include which of the following?

I. HSO₄⁻ II. H₂O III. SO₄²⁻

• II only

• III only

• I and II

• II and III

Calculate the pH of a solution prepared by dissolving 0.37 mol of formic acid (HCOOH) and 0.23 mol of sodium formate (NaCOOH) in water sufficient to yield 1.00 L of solution. The K_a of formic acid is 1.8 x10^-4.

• 2.1

• 3.54

• 10.46

• 2.31

Calculate the pH of a solution prepared by dissolving 0.750 mol of NH₃ and 0.250 mol of NH₄Cl in water sufficient to yield 1.00 L of solution. The K_b of ammonia is 1.8 x10^-5.

• 5.22

• 4.27

• 9.73

• 8.78

Which of the following reactions shows what happens when nitric acid is added to an ammonia /ammonium ion buffer?

• H⁺ + NH₃ ⇌ NH₄⁺

• H⁺ + NH₄⁺ ⇌ NH₅²⁺

• NO₃^- + NH₃ ⇌ NH₃NO₃

• NO₃^- + NH₄ ⇌ NH₄NO₃

A 1.0-liter solution contains 0.25 M HF and 0.60 M NaF (Ka for HF is 7.2 x 10^-4)

What is the pH of this solution?

• 1.40

• 3.52

• 4.63

• 2.81