Question

8. Calculate the hydrogen ion concentration of the weak acid in each of the following solutions. Note that the ionization constants may be such that the change in electrolyte concentration cannot be neglected and the quadratic formula or successive approximations may be required.
(a) 0.0184 M HCNO ( Ka = 3.46 x 10 - 4 ) (b) 0.02173 M CH2 ClCO2 H ( Ka = 1.4 x 10 -3 )

Answer 1

A.

Step 1. Write the dissociation equation.

Step 2. Take reaction to equilibrium.

	HCNO	CNO -	H+
initial	0.0184 M	0	0
change	- x	+ x	+ x
equilibrium	0.0184 - x	x	x

Step 3. Write the dissociation constant.

Step 4. Add the known values to the latter equation.

Step 5. Solve for x = [H⁺].

B.

Step 1. Write the dissociation equation.

Step 2. Take reaction to equilibrium.

	ClCOOH	ClCOO -	H+
initial	0.02173 M	0	0
change	- x	+ x	+ x
equilibrium	0.02173 - x	x	x

Step 3. Write the dissociation constant.

Step 4. Add the known values to the latter equation.

Step 5. Solve for x = [H⁺].