Question

the density of 3m solution of NaCL is 1.25g ml-1.calculate molality of solution (Molar mass of Nacl is 58.5mol-1
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Answer 1

Answer:

In the given question, we have been provided with the molarity and density of the solution. Therefore, we need to use these two terms and establish such a relation so as to calculate the molality of the solution.

Complete step by step solution:

Concentration is basically a measure to find the amount of solute present in solvent which together forms a solution. Molality is a term to express the concentration of a solution.

Molality of any solution is defined as, “the number of moles of solute present per kg of solvent”. Therefore, its unit is mol/kg.

It is denoted by ‘m’.

The formula of molality is –

Molality=moles of solute (mol)weight of solvent (kg)x1000

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Molality can be related to molarity using the density of the solution as –

m=M x 10001000ρ−M x w

Where,

M = Molarity = moles solute/Litre solution

M = molality = moles solute/kg solvent

ρ

= density = g solution/ mL solution

w = molecular weight (molar mass) of solute in g/mole = 58.44 g/mol

Therefore, putting all the values, we get –

m=3 x 1000(1000 x 1.25)−3 x 58.44

m = 2.79 mol/kg.

Therefore, the answer is – The molality of the given solution is 2.79 mol/kg.

Additional information: We can convert Molality to Molarity by the following formula: M=1000x m xρ1000+m x w

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