Question

In: Chemistry

A 0.148-M solution of X (Mm = 177 g/mol) has a density of 1.156 g/ml. What...

A 0.148-M solution of X (Mm = 177 g/mol) has a density of 1.156 g/ml. What is the molality of X in the solution?

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Expert Solution

Molarity = 0.148 = (solute weightgr/mol.wt)(1/1L)
we have mol.wt = 177g/mol

Therefore, solute weight= molarity x molecular weight
                       = 0.148 x 177
                       = 26.196 g
                      
Weight of 1000 ml of solute = 1000 mL x density
                           = 1000 mL x 1.156 g/mL
                           = 1156 g
weight of the solvent in 1156 g of solution = 1156 g - 26.196 g
                                           = 1129.8 g
                  
                  
                  
Molality = no. moles of solute present in 1 kg (or 1000 g) of the solvent.

therefore, molality = (Weight of Solute/Mol. weight)(1000/solvent weight in grams)
                   = (26.196 g/177 g/mol)(1000/1129.8 g)
                   = 0.131 m
                  
Molality of the solution = 0.131 m


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