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A metal, M, of atomic weight 96 reacts with fluorine to form a salt that can be represented as MFx. In order to determine x and therefore the formula of the salt, a boiling point elevation experiment is performed. A 9.18-g sample of the salt is dissolved in 100.0 g of water and the boiling point of the solution is found to be 374.38 K.

(A) MF
(B) MF2
(C) MF3
(D) MF4

User Mark KWH
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1 Answer

7 votes

Answer:

The correct answer is option 3.

Step-by-step explanation:

Molecular formula of the salt =
MF_x

The salt when dissolved in water will get dissociated into ions.


MF_x\rightarrow M^(x+)+xF^-

van't Hoff factor = i = 1+x

Boiling point of the solution =
T_b=374.38 K

Boiling point of pure solvent that water =
T=373.15 K

Elevation in boiling point =
\Delta T_b


\Delta T_b=T_b-T=374.38 K-373.15 K=1.23 K


\Delta T_b=i* K_b* m


K_b=molal elevation constant

m = molality of the solution

Molal elevation constant of water =0.52 K kg/mol

molality =
\frac{\text{Mass of compound}}{\text{Molar mass of compound}* \text{mas of solvent in kg}}


m=(9.18 g)/((96 g/mol+x* 19 g/mol)* 0.100 kg)


1.23 K=i* 0.52 K kg/mol* (9.18 g)/((96 g/mol+x* 19 g/mol)* 0.100 kg)

i = 2.47+0.48x

2.47+0.48x = 1+x

x =2.8 ≈ 3

Molecular formula of the salt =
MF_3

User Lauri Lehtinen
by
8.9k points

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