Is a copper(II) bromide solution at #1.00*mol*L^-1# concentration HYPERTONIC with respect to #NaCl(aq)# at the SAME concentration?

1 Answer
Nov 26, 2016

Answer:

The #"cupric bromide"# is HYPERTONIC with respect to a #0.30# #"osmolar"# solution of saline. I assume that red blood cells have an osmolairty of #0.30# #"osmolar"# (this is not specified in the question.)

Explanation:

#"Osmolarity"# refers to the number of solute ions in solution. A #1.0*mol*L^-1# concentration of sodium chloride is #"2 osmolar"#, because sodium chloride speciates in aqueous solution to stoichiometric #Na^+(aq)# and #Cl^(-)(aq)# ions.

Upon dissolution, #"cupric bromide"# gives three equiv of ions:

#CuBr_2(s) + "excess "H_2O(l) rarr Cu^(2+)(aq)+2Br^(-)(aq)#

And thus #1.00*mol*L^-1# #CuBr_2(aq)# is #"3.00 osmolar"#.

On the other hand, a #0.30# #"osmolar"# solution of saline, has a concentration of #0.15*mol*L^-1# with respect to sodium chloride. Clearly, the solution of the copper salt is more concentrated, and expresses a greater osmolarity.