Question

Assuming complete dissociation of the salts, what is the ionic strength of a solution containing formal concentrations of 0.2 mM MgCl2 and 0.3 mM AlCl3?

A.0.6 mM

B.1.8 mM

C.2.0 mM

D.2.4 mM

E.4.8 mM

A mass balance equation for a solution of 0.10 M H2B+ solution may be which of the following?

A.[H+] + [H2B+] = [B-] + [OH-]

B.[H+] = [H2B+] + [HB] + [B-]

C.0.10 M = [H2B+]

D.0.10 M = [H+] + [OH-]

E.0.10 M = [H2B+] + [HB] + [B-]

What is the theoretical pH of 0.011 μM KOH?

A.6.00

B.6.98

C.7.00

D.7.02

E.8.00

Answer 1

Ans 1

Complete dissociation of MgCl2

MgCl2 = Mg2+ + 2Cl-

Concentration of Mg2+ C1 = 0.2 mM

Charge on Mg2+ Z1 = 2

Concentration of Cl- C2 = 2*0.2 = 0.4 mM

Charge on Cl- Z2 = 1

Complete dissociation of AlCl3

AlCl3 = Al3+ + 3Cl-

Concentration of Al3+ C3 = 0.3 mM

Charge on Al3+ Z3 = 3

Concentration of Cl- C4 = 3*0.3 = 0.9 mM

Charge on Cl- Z4 = 1

ionic strength of a solution

= 0.5 x [(C1 x Z1² ) + (C2 x Z2² ) + (C3 x Z3² ) + (C4 x Z4²)]

=0.5 x [(0.2 x 2² ) + (0.4 x 1² ) + (0.3 x 3² ) + (0.9 x 1²)]

= 0.5 x (0.8 + 0.4 + 2.7 + 0.9)

= 2.4 mM

Option D is the correct answer