Initially 22.2 g of calcium chloride are dissolved in water to make a 500 mL solution. Then the solution is again diluted upto 2000 mL. Calculate the molarity of Cl− ions in the final solution if the 80% of the given salt dissociates in the final solution:
Molar mass of the CaCl2=(40+71) g/mol=111 g/mol
Given, mass of CaCl2 = 22.2 g
So, moles of CaCl2 present =22.2111=0.2 mol
one formula unit of CaCl2 contains 2 Cl− ions.
So, 0.2 moles of CaCl2 should produce 0.4 moles of Cl− ions.
But in the question, we are given that only 80% of CaCl2 dissociates in the final solution.
Thus, moles of Cl− ions produced =0.4×0.8=0.32 mol
Hence molarity of the Cl− ions in the final solution
(Since volume of the final solution is 2000 mL)