Question

the mole fraction of Nacl in 4.5molal aqueous solution of nacl
(a) 0.39(b) 0.057(c) 0.075(f) 0.57​

Answer 1

Answer:

Answer would be Option (c) 0.075

Explanation:

4.5 molal of NaCl means that 4.5 moles of NaCl is present in 1 litre of solvent (here, Water)

No. of moles of NaCl =4.5 moles

No. of moles of water =1000/18 = 55.5 moles

therefor mole fraction of NaCl =4.5/(4.5+55.5) =0.0749

Answer 2

Given:

4.5 Molal aqueous solution of NaCl is provided.

To find:

Mole fraction of NaCl ?

Calculation:

4.5 Molal solution means :

• 4.5 moles of NaCl in 1 Kg of solvent (here water).

So, moles of water be :

$n_{water} = \dfrac{1000\:g}{18\:g/mol} = 55.5 \: moles$

Now, mole fraction:

$\therefore \: \chi_{NaCl} = \dfrac{ n_{NaCl}}{ n_{water} + n_{NaCl} }$

$\implies \: \chi_{NaCl} = \dfrac{4.5}{4.5 + 55.5}$

$\implies \: \chi_{NaCl} = \dfrac{4.5}{60}$

$\implies \: \chi_{NaCl} = 0.075$

So, mole fraction of NaCl is 0.075 .