In: Chemistry
A solution is prepared by dissolving 171g of CdCl2 in enough water to make 250.0 mL of solution. If the density of the solution is 1.556 g/mL, calculate: Molarity of the solution, mole fraction of CdCl2, and molality of the solution.
Step 1, -
Calculate number of moles of CdCl2 dissolved in water to prepare 250ml solution
...........................................................................= Wt. of CdCl2 / Molecular mass of CdCl2 ...........................................................................= 171 / 183.41............................................
...........................................................................= 0.9323 moles............................................
.................. number of moles per litre of solution = ( 0.9323 x 1000) / 250...= 3.7292 moles
Step 2`, - Calculation of Molarity (M) of Cd Cl2 Soln.
Since, Molarity (M) = Number of moles per litre of solution
...........................= 3.7292 M
..........................or, = 3.73 M
Step 3 ,
Calculation fpr molality of CdCl2 solution :
.....................................Given density of solution = 1.556 gms / ml
weight of 1000 ml of solution = 1.556 x 1000 = 1556 gms.
Now 1556 gms of solution contains CdCl2 .......... = 3.73 moles
...............................................................................= 3.73 x 183.414
............................................................................... = 684.13 gms
hence , weight of water in one litre or 1000 gms of solution = (1556 - 684.13) gms
................................................................................................ = 871 .87 gms
So , 871.87 gms of water in solution contains the number of moles of CdCl2 = 3.73 moles
1000 gms ( or 1 Kg ) of water in solution.....................................= ( 3.73 x 1000 ) / 871. 87
........................................................................................................................... = 4.278 moles
....................................................................................................................or,... = 4.28 moles
Step -4 ,
Now, we know that molality of a solution = Number of moles of solute per Kg of solvent
therefore this represents the molality ( m) of prepared CdCl2 solution as ..........= 4.28 m
step 3 ,-
Calculation of mole fraction of CdCl2
Since mole fraction of solute = moles of solute / total of the (number of moles of solute + moles of solvent )
Therefore, mole fraction of CdCl2 = 4.28 / 4.28 + (1000/18 )
.....................................................= 0.0715
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