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A solution containing 1.8 g of a compoun...

A solution containing 1.8 g of a compound (empirical formula `CH_(2)O`) in 40 g of water is observed to freeze at `-0.465^(@)C`. The molecular formula of the compound is (`k_(f)` of water = 1.86 kg K `mol^(-1)`)

A

a) `C_(2)H_(4)O_(2)`

B

b) `C_(3)H_(6)O_(3)`

C

c) `C_(4)H_(8)O_(4)`

D

d) `C_(6)H_(12)O_(6)`

Text Solution

Verified by Experts

The correct Answer is:
D
`Delta T_(f) = K_(f) xx m`
`because" "Delta T_(f) = T_(f)^(@) - T_(f)`
`= 0^(@) - (-0.465^(@)) = 0.465^(@)C`
`therefore" "0.465 = 1.86 xx (1.8)/(M) xx (1000)/(40)`
or M = 180
empirical formula weight `= 12 + 1 xx 2 + 16`
= 30
`because" "n = ("molecular weight")/("empirical formula weight") = (180)/(30) = 6`
`therefore` Molecular formula `= (CH_(2)O)_(6)`
`= C_(6)H_(12)O_(6)`
Thus, molecular formula of compound
`= C_(6)H_(12)O_(6)`
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