how is

m= w2/m2 // w1/1000

?

how did it come?

Dear Student,

The correct expression of molality is [(w₂ / M₂.) / w₁ ] x 1000

m is known as molality of solute. It is defined as number of moles of solute in 1 kg of solvent.

Let us suppose that w₂ g of solute with M₂ g/mol of molar mass is dissolved in w₁ g, of solvent.

Number of moles of solute = w₂ / M₂.

Thus, Molality, m = (w₂ / M₂.) / w₁ in grams.

Since molality is moles/kg, therefore, we need to convert mass of solvent from g to kg.

So, m = [(w₂ / M₂.) / w₁ in kg] x 1000

Hope its clear now.

Enjoy learning!!