Answer to Question #134632 in General Chemistry for Kailey

Question

Determine the molar concentration of the anion (negative ion), if 1.2g of magnesium chloride, MgCl2(s) is dissolved in enough water to make 2.0L of solution.

Answer 1

magnesium Chloride dissolves in water to form Mg²⁺ ions and Cl^- ions in a reversible process.

MgCl₂(s) $\iff$ Mg²⁺ (aq) + 2Cl^- (aq) in presence of water

mass of MgCl₂ = 1.2g and the volume of solution =2.0 L

$molarity = (Moles of solute)/ (litre volume of solution)$

calculating moles of magnesium Chloride

$mol = mass/molecular weight$

molecular weight of MgCl₂ = 24.0 +35.5 +35.5 = 95g

$moles = 1.2 / 95 = 0.01263$

mole ratio of MgCl₂ : Cl^- = 1:2

moles of chloride ions = 0.01263 * 2 =0.02526 moles of Chloride ions.

Molarity /concentration of Cl^- is

$M = 0.02562 mol / 2.0L = 0.0126 M$ Or 0.0126 mol/L