# Problem: During the analysis of an unknown acid, HA, a 0.010 M solution of the sodium salt of the conjugate base, Na+A–, was found to have a pH of 10.35 at 25 °C.Using Table 10.1, identify the unknown acid, HA.Hydrofluoric acid               HF                          7.2X10-4  Acetic acid                         CH3COOH             1.8X10-5Hypobromouss acid          HIO                        2X10-9Hydrocyanic acid               HBrO                     6.2X10-10 Hypoiodous acid                HIO                       2X10-11A. HIO, hypoiodous acidB. HF, hydrofluoric acidC. HCN, hydrocyanic acidD. CH3COOH, acetic acidE. HBrO, hypobromous acid

###### FREE Expert Solution

We are being asked to calculate the Ka of the unknown acid, HA  if a 0.010 M solution of the sodium salt of the conjugate base, Na+A, was found to have a pH of 10.35 at 25 °C.

NaA is a salt and it will break up in the solution:

NaA(aq) → Na+(aq) + A-(aq)

concentraion of NaA = concentration of A-

A- is the conjugate base of the unknown acid HA:

HA(aq)    +   H2O(l)    →    A-(aq)    +     H3O+(aq)
(weak acid)                        (conjugate base)

We're going to calculate Ka of HA using the following steps:

Step 1. Create an ICE chart for the equilibrium reaction of the conjugate base A-.
Step 2. Write the Kb expression for A-.
Step 3. Calculate the pOH of and OH- concentration from the pH.
Step 4. Calculate Kb.
Step 5. Calculate Ka of HA from Kb of A-.

Step 6. Identify the unknown acid.

92% (350 ratings) ###### Problem Details

During the analysis of an unknown acid, HA, a 0.010 M solution of the sodium salt of the conjugate base, Na+A, was found to have a pH of 10.35 at 25 °C.

Using Table 10.1, identify the unknown acid, HA.

Hydrofluoric acid               HF                          7.2X10-4
Acetic acid                         CH3COOH             1.8X10-5
Hypobromouss acid          HIO                        2X10-9
Hydrocyanic acid               HBrO                     6.2X10-10
Hypoiodous acid                HIO                       2X10-11

A. HIO, hypoiodous acid

B. HF, hydrofluoric acid

C. HCN, hydrocyanic acid

D. CH3COOH, acetic acid

E. HBrO, hypobromous acid