Question

The mole fraction of ethanol in an aqueous solution is 0.1 .Then find its molality? a) 5.2 b) 6.7 c) 5.8 d) 6.5​

Answer 1

Explanation:

Morality (m)

Massofsolventinkg

Noofmolesofsolute

∴m=

Molecularweightofsolute(M

A

)

weightofsolute(w

A

)

×

weightofsolvent(W

B

)

1000

m=

M

A

W

A

×

W

B

1000

×

M

B

M

B

=

n

B

n

A

×

M

B

1000

n

A

= no of moles of solute m=

n

B

n

A

×

M

B

1000

×

(n

A

+n

B

)

(n

A

+n

B

)

n

B

= no of moles of solvent

∴

m=

x

B

x

A

×

M

B

1000

...(1) x

A

= mole fraction of solute

x

B

= mole fraction of solvent

Given :- x

A

=0.040 Also x

A

+x

B

=1⇒x

B

=0.960

Ethanol is solute 1 water is solvent ∴M

B

=19

Putting values of x

A

,x

B

&M

B

in (1), we get

m=

0.960

0.040

×

18

1000

⇒

m=2.31mol/kg

Answer 2

Correct Question

The mole fraction of ethanol in an aqueous solution is 0.1 .Then find its molality? a) 5.2 b) 6.17 c) 5.8 d) 6.5​

Answer:

The molality of the solution is  6.17 $mol/kg$ and option (b) is correct.

Explanation:

Given:

The mole fraction of ethanol in an aqueous solution is 0.1.

To Find:

The molality of the solution.

Formula Used:

Molality (m)  can be  defined as the number of moles of solute per kilogram of solvent.

$Molality (m)=\frac{ moles\ of \ solute}{kilograms\ of\ solvent}$

Solution:

As given,the mole fraction of ethanol in an aqueous solution is 0.1.

Mole fraction of ethanol = 0.1

Mole fraction of water $= 1-0.1=0.9$

0.9 mol of water $=\frac{0.9\times18}{1000} =0.0162 \ kg$

Therefore, the molality of the solution $=\frac{0.1}{0.0162} =6.17\ mol/kg$

Thus,the molality of the solution is  6.17 $mol/kg$ and option (b) is correct.

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