Question

A 0.674M cobalt (II) chloride (CoCl2) solution is prepared with a total volume of 0.0750L. the molecular weight of CoCl2 is 128.9 g/mol. What mass of CoCl2 in grams is needed for this solution?

Answer 1

Mass of $CoCl_{2}$ is 6.515 g.

Explanation:

This question is solved by Molarity formula.

Concentration of solutions expressed in terms of Molarity. Molarity is described as the number of moles of solute per litre of solution.

                       

                         $Molarity=\frac{Number of moles}{volume(L)}$

As we know,    $Moles=\frac{Weight of solute(gm)}{Molecular weight of solute}$

Given that-

Molarity of solute ($CoCl_{2}$) = 0.674 M

Volume of solution = 0.0750 L

Molecular weight of solute = 128.9 $\frac{g}{mol}$

So,

            $Molarity=\frac{Weight of solute(gm)}{Molecular weight of solute\times volume (L)}$   ........(i)

Put the above values in equation (i)

                        $0.674=\frac{weight of solute}{128.9\times 0.0750}$

           $weight of solute (CoCl_{2})=6.515 g$

Therefore, 6.515 g of $CoCl_{2}$ is needed for 0.674 M and 0.0750 L solution.

Answer 2

Given,

Molarity of a cobalt (II) chloride (CoCl2) solution = 0.674M

The total volume of the solution = 0.0750L

The molecular weight of CoCl2 = 128.9 g/mol

To find,

The total mass of CoCl2 in grams, needed for preparing this solution.

Solution,

We can simply solve this numerical problem by using the following process:

As per the principles of stoichiometry,

Molarity of a solution (M)

Molarity of a solution (M)= (Moles of solute in the solution) / (Total volume of the solution)

On applying the formula for the given cobalt (II) chloride (CoCl2) solution, we get :

Molarity of a solution (M)

= (Moles of solute in the solution) / (Total volume of the solution)

=> 0.674M = (Moles of CoCl2 in the solution) / (0.0750L)

=> Moles of CoCl2 in the solution = 0.05055

Now, as per stoichiometry,

(Moles of any compound) x (Molar mass if the compound) = total mass of the compound

=> total mass of CoCl2 = 0.05055 moles x 128.9

g/mol

(Since the molar mass of any compound = the molecular weight of that compound)

=> total mass of CoCl2 = 6.516 grams

Hence, approximately 6.516 grams of CoCl2 is needed for preparing the solution.