Question

If 0.2 g of nitrobenzene are added to 10.9 g of naphthalene, calculate the molality of the solution. (given: molar mass of nitrobenzene = 123.06 g/mole) report answers to one decimal place

Answer 1

Molality is defined as 1 mole of a solute in 1 kg of solvent.  

Molality=

$\frac{Number of moles of solute}{Mass of solvent in kg}$

Number of moles of solute, n=  

$\frac{Given mass of the substance}{Molar mass of the substance}$

Given mass of the nitrobenzene=0.2 g

Molar mass of the substance= 123.06 g mol⁻¹

Number of moles of nitrobenzene,  

$n= \frac{0.2 }{123.06}$

Number of moles of nitrobenzene, n= 0.0016  mol

Mass of 10.9 g of naphthalene in kg=0.0109  

$Molality= \frac{0.0016}{0.0109 }$

Molality= 0.146 m