What is the concentration of chloride ion in a solution composed by mixing #447.2*mL# of #0.216*mol*L^-1# #NaCl#, and #100.8*mL# of #0.358*mol*L^-1# #CaCl_2#. Why would this not be applicable to a solution of #PCl_3# added to water?

We can assess #[Cl^-]# with respect to the sodium chloride and the calcium chloride solutions.....We cannot do so in relation to the #PCl_3# as we will see later.....

For #NaCl# and #CaCl_2# we assume that the concentrations are ADDITIVE, and we use the old ratio....

#"concentration"="moles of solute"/"volume of solution"#

And thus #"moles of solute"="concentration"xx"volume"#

#"Moles of NaCl"=447.2xx10^-3*Lxx0.216*mol*L^-1=0.0966*mol" (i)"#

#"Moles of CaCl"_2=100.8xx10^-3*Lxx0.358*mol*L^-1=0.0361*mol" (ii)"#

And so we take....#((i)+2xx(ii))/("combined volume")#

#[Cl^-]=(0.169*mol)/(0.548*L)=0.308*mol*L^-1#....

As for the #PCl_3#, it is a fact that liquid #PCl_3# REACTS with water to give phosphorous acid and hydrogen chloride....

#PCl_3(l) + 3H_2O(l) rarr H_3PO_3(aq) + 3HCl(aq)#

And thus we could not have a solution of #PCl_3# in water or in ethanol; we COULD have such a solution in petroleum ether or methylene chloride, but these solvents are insoluble in water.

This reaction between phosphorus trichloride and water is very violent and not one that I would do with these quantities.....and so the question is VERY poorly proposed....