0.2 mole of HCl and 0.1 mole of CaCl₂ were dissolved in water to have 500 ml of solution, the molarity of Cl^- ions is

(1)0.04 M (2)0.8 M (3)0.4 M (4)0.08 M

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Solution

The dissociation reactions are
HCl ⇔ H+ + Cl- and CaCl2 ⇔ Ca2+ + 2Cl-

Moles of Cl- formed from 0.2 moles of HCl = 0.2 moles
Moles of Cl- formed from 0.1 moles of CaCl2 = 2 X 0.1 = 0.2 moles
Total moles of Cl- = 0.4mol
Volume of solution = 500ml = 0.5L
Molarity of Cl- = moles Cl-/Volume of solution = 0.4/0.5 = 0.8M

Molality = moles of solute/mass of solvent in Kg
Density of water =1g/ml
So, mass of 500ml water =500g = 0.5Kg

Molality = 0.4/0.5= 0.8m
so option(2)

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