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What will be the freezing point of 0.2 m...

What will be the freezing point of 0.2 molal aqueous solution of `MgBr_(2)` ? If salt dissociates 40% in solution and `K_(f)` for water is 1.86 KKg `mol^(-1)`

A

`-3.35^(@)`C

B

`-0.67^(@)`C

C

`-0.6^(@)`C

D

`-0.45^(@)`C

Text Solution

Verified by Experts

The correct Answer is:
B
`Delta T_(f)=ixx(1000K_(f)w)/(mW)`
`DeltaT^(f)=ixxK_(f)xx"molality`
`MgBr_(2)hArrMg^(+2)+2Br^(-)`
`i=1-alpha+3alpha`
`=1-0.4+3xx0.4=1.8`
`:.DeltaT_(f)=1.8xx1.86xx0.2`
and `T_(1)T_(f)-DeltaT=-0.67^(@)`C
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