Question

A derivative of the polysaccharide chitosan is being utilized in a spray to treat severe wounds. The chitosan aids in quickly stopping the flow of blood by forming a gel at the wound site. The behavior of the gel is strongly dependent upon the activity of ionic species in the spray. In one process to form the spray, an aqueous solution containing 0.002 M NaCl and 0.006 M CaCl2 is mixed with a solid powder of the chitosan derivative.

(a) What is the ionic strength of the precursor solution, before the chitosan is added? (I got 0.02M for the answer and want to check if it is correct)

(b) Use the Debye-Huckel expression to calculate the activity coefficient of Na+ , Cl- , and Ca2+ in the precursor solution at 25 C.

Answer 1

a) you have a concentration of 0.002M of NaCl, this means you have 0.002M of Na⁺ and 0.002M of Cl^-,

and 0.006M of the CaCl2 you have 0.006M 0f Ca²⁺ and 2x0.006M of Cl^-

.

c is the concentration of each ion and z is the charge raised to the second power

b) the simplified form of the Devye-Huckel equation at 25°C (298K) is:

The activity coefficient depends on the charge of the ions so, for the +1 or -1 (Cl and Na) the activity coefficient is:

For Calcium