Calculate the pH of a solution formed by mixing 120.0 mL of 0.30 M HClO with 1180.0 mL of 0.20 M KClO.The K_a for HClO is 2.9 × 10^-8. A) 5.99 B) 8.01 C) 7.54 D) 7.06 E) 6.46

Question

Quizplus · Accepted Answer

The balanced equation for the reaction between HClO and KClO is:

HClO + KClO ⇌ H+ +ClO- + K+

Since the acid HClO is weak, we can use the equilibrium constant expression (Ka) to find the concentration of H+:

Ka = [H+][ClO-]/[HClO]

[H+]=Ka[HClO]/[ClO-]

We can use an ICE table (initial, change, equilibrium) to find the concentrations of species at equilibrium.

Initial concentrations:

[HClO] = 0.30 M

[KClO] = 0.20 M

Change in concentrations:

Since the volumes are added together, we can assume that the total volume is 1200 mL.

[HClO] decreases by x M (stoichiometric coefficient is 1)

[ClO-] increases by x M (stoichiometric coefficient is also 1)

[K+] does not change since it is a spectator ion.

Equilibrium concentrations:

[HClO] = 0.30 - x M

[ClO-] = 0.20 + x M

Since x is assumed to be very small compared to the initial concentrations, we can simplify the expression for Ka:

Ka = [H+][ClO-]/[HClO]

Ka ≈ [H+][ClO-]/0.30

[H+]=Ka*0.30/[ClO-]

[H+]=2.9×10-8*0.30/[0.20 + x]

[H+]=4.35×10-8 M

pH=-log[H+]=7.54.

Therefore, the answer is choice C.

Calculate the PH of a Solution Formed by Mixing 120