A mass of 12.0 g of calcium chloride is diluted to a volume of 250 mL in a volumetric flask.Which of the equations below is a correct method for determining the chloride ion concentration?

Question

Quizplus · Accepted Answer

To find the chloride ion concentration, we need to use stoichiometry to convert the mass of CaCl2 to the number of moles of Cl-.

First, we need to calculate the number of moles of CaCl2 using its molar mass: 
12.0 g / 111.0 g/mol = 0.1081 mol CaCl2

Now we can use the balanced chemical equation for CaCl2: 
1 CaCl2 → 2 Cl-

So, for every 1 mole of CaCl2, we have 2 moles of Cl-. Therefore, we can multiply the number of moles of CaCl2 by 2 to get the number of moles of Cl-: 
0.1081 mol CaCl2 x 2 mol Cl-/1 mol CaCl2 = 0.2162 mol Cl-

Finally, we need to convert this to concentration (in units of mol/L, or M) by dividing by the volume of the solution in liters: 
0.2162 mol Cl- / 0.250 L = 0.865 M Cl-

The correct equation for this calculation is C) $\frac{12.0 \mathrm{~g} \mathrm{~CaCl}_{2}}{250 \mathrm{~mL}}\left(\frac{1000 \mathrm{~mL}}{1 \mathrm{~L}}\right)\left(\frac{1 \mathrm{~mole} \mathrm{CaCl}_{2}}{111.0 \mathrm{~g}}\right)\left(\frac{2 \mathrm{~mol} \mathrm{Cl}^{-}}{1 \mathrm{~mol} \mathrm{CaCl}_{2}}\right)$

A Mass of 12 B) C) D) E)