`30 mL` of `0.1M KI_(aq.)` and `10 mL` of `0.2M AgNO_(3)` are mixed. The solution is then filtered out. Assuming that no change in total volume, the resulting solution will freezing at:
`[K_(f) "for" H_(2)O = 1.86K kg mol^(-1)`, assume molality = molality]

Options

A. (a) `0.22`
B. (b) `0.28`
C. ( c) `0.149`
D. (d) `0.074`

Answer

B

Explanation

`{:(,KI,+,AgNO_(3),rarr,KNO_(3)+,AgI),("milli-mole",30xx0.1,,10xx0.2,,,),(,=3,,=2,,0,0),("milli-mole left",1,,0,,2,2):}`
`:. [KI]` in solution `= (1)/(40)` and `[KNO_(3)]`
`= (2)/(40)`
`"molarity = molality"`
`:. Delta T_(f) = Delta T_(f) ("by" KI) + Delta T_(f) ("by" KNO_(3))`
`= "molality" xx 1.86 xx (1+alpha_(1)) + "molality" xx 1.86 xx (1+alpha_(2))`
`= (1)/(40) xx 1.86 xx 2+(2)/(40) xx 1.86 xx 2`
`= 0.093 + 0.186 = 0.279 ~~ 0.28`