Question

What is the melting point of a solution in which 2.5 grams of sodium chloride is added to 230 mL of water?

Answer 1

Well, what is the `"molal freezing point depression constant"` of water, `K_f`?

Explanation:

And this depends on the number of particles in solution....and so here the molality is given by...

`m_"NaCl"=((2.50*g)/(58.44*g*mol^-1))/(230*mLxx10^-3*kg*mL^-1)=0.186*mol*kg^-1`

But the concentration of IONS in solution is TWICE this value given the reaction of common salt with water:
`NaCl(s) stackrel(H_2O)rarrunderbrace(Na^+ + Cl^-)_"2 equiv of ion"`

And so `T_"freezing point depression"=2xx0.186*mol*kg^-1xxk_f`..

...but we don't know what `k_f` is ... it should have been quoted with the question....