Chem 0200 pH and buffers part 1

The concentrations of HCl and C₆H₅COOH are both 0.025moldm^–3. Why is the pH different for these two acids, even though they have the same concentration?

The concentration of HCl is 0.025 mol dm^–3. What is the pH of the HCl?

• 1.1

• 1.6

• 2.4

• 4.3

Three monobasic acids X, Y and Z all have a concentration of 0.011 mol dm^–3. The pK_a of X is 5.61, the K_a of Y is 4.13 × 10^–7 and the pH of Z is 4.78. What is the order of the acids in terms of increasing acid strength?

• X < Y < Z

• Z < X < Y

• Y < X < Z

• Z < Y < X

The concentration of C₆H₅COOH is 0.025 mol dm^–3. What is the pH of the benzoic acid at 25°C, given the K_a at this temperature is 6.3 × 10^–5mol dm^–3?

• 0.0013

• 2.9

• 5.5

• 1.6

Define weak acid.

Define K_a.

In an aqueous solution, carbonic acid forms a weak acid solution containing the hydrogen carbonate ion. Write an equation to represent the dissociation of carbonic acid in aqueous solution.

Write the K_a expression for the reaction in which carbonic acid forms a weak acidic solution containing the hydrogen carbonate ion.

Calculate the pH of a 0.100 mol dm^‒3 aqueous solution of carbonic acid. (Ka = 4.5 × 10^‒7 mol dm^–3 at 25^oC.)

• 10.3

• 1

• 13

• 3.7

The acid dissociation constant (K_a) of ethanoic acid at 25°C has a numerical value of 1.7 x 10^-5. The equilibrium equation for the dissociation of ethanoic acid is

CH₃COOH_(aq) ⇌ H⁺ _(aq) + CH₃COO^–_(aq).

Calculate the equilibrium concentration of ethanoic acid in a solution that has a pH of 5.

• 1.7 x 10^-5 mol dm^–3

• 1 x 10^-5 mol dm^–3

• 2 x 10^-5 mol dm^–3

• 5.9 x 10^-6 mol dm^–3