Question

A student was asked to define molality. Then he answered that it is the number of gram moles of the solute dissolved per litre of the solution.

1. Is it correct?

2. Can you help the student to dene molality?

3. Calculate the molality of a solution containing 20 g of NaOH in 250 g of H₂O.

Answer 1

1. It is not correct.

2. It is the number of moles of the solute present in 1000 g of the solvent. Molality can be determined by using the formula. Molality, m = \(\frac{Mass\,of\, the\,solute\,in\,gram\, \times \,1000}{Molar\,mass\, of \,the\, solute\,\times Mass\, of \,the\, solvent\, in \,gram}\) 

3. Molality, m = \(\frac{20\times 1000}{40\times \,250}\) = 2 m