Question

A.CALCULATE THE CRYOSCOPIC CONSTANT OF H2O. USE IT TO ANSWER THE FOLLOWING: a WEAK ACID HX is dissolved in water. A 0.250 molal solution has a freezing point of 0.5 C. calculate the value of ka for the acid, where Ka is the equilibrium constant for
HX<--=-->H+ + X-
Ka = [X-][H+]/[HX]

I assume you have the cryoscopic constant for water. I will assume, further, that it is 1.86 degrees C/m.
(delta T)=i*k_f*m
delta T is 0.5^o C
solve for i
k_f=1.86<sup>o</sub>C/m.
m is molality = 0.250 mol/kg

i*m(ideal)=m(effective)
where m(ideal) is 0.250.

HX <===>H^+ + X^-
When HX ionizes,
(H^+) = Y
(X^-) = Y
(HX) = 0.250 - Y
The sum of HX + H^+ + X^- =
0.250-Y+Y+Y=m(effective).
m(effective is from above).
Solve for Y and then for Ka.
Post your work if you get stuck.
Check my thinking. Check my work carefully.


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