Question

A student prepares a solution by placing 0.355 g of niso4 · 6 h2o and 0.137 g of nicl2 · 6 h2o in a 250-ml volumetric flask. a small amount of distilled water is then added, and the compounds are swirled in the flask until they dissolve. after they have dissolved, the solution is diluted to the mark. what is the molar concentration of cl− ions in the final solution? answer in units of m.

Answer 1

Answer : The molarity of Cl- ions is 0.00461M

Explanation :

Step 1 : Find moles of NiCl₂.6H₂O.

The moles of a substance are calculated as

$mole = \frac{Grams}{Molar Mass}$

The molar mass of NiCl₂.6H₂O is calculated as follows.

Ni + 2Cl + 12H + O = 58.69 + 2(35.45) +12 (1.01) + 6(16) = 237.71 g/mol

Moles of NiCl₂.6H₂O = $\frac{0.137g}{237.71 g/mol}$

Moles of NiCl₂.6H₂O = 0.000576

Step 2 : Use mole ratio to find moles of Cl

There are 2 moles of Cl in 1 mol of NiCl₂.6H₂O.

Therefore the mole ratio of NiCl₂.6H₂O and Cl- is 1:2

The moles of Cl- = 2 x 0.000576 = 0.00115

Step 3 : Find molarity of Cl

The molarity of Cl- can be calculated as,

$M = \frac{mol (Cl-)}{L(solution)}$

The final volume of the solution is 250 mL = 0.25 L.

$M=\frac{0.00115mol}{0.25L} = 0.00461$

The molarity of Cl- ions is 0.00461M