Question

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?

Answer 1

This question is very poorly proposed.....

Explanation:

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....