Question

How many moles of CoCl₃​ are in 172.6 ml of a 19.6 mass % solution of CoCl₃​ which has a density of 1.206 g/ mL? __________

Answer 1

Given:

Volume of CoCl₃ solution = 172.6 mL

Density of CoCl₃ solution = 1.206 g / mL

Let us find Mass of CoCl₃ solution = ?

Formula,

Density = Mass / Volume

1.206 g/mL = Mass / 172.6 mL

Mass = 1.206 g/mL x 172.6 mL

Mass = 208.2 g.

i.e. Mass of CoCl₃ solution = 208.2 g

But it is given that it is 19.6 (%w/V) CoCl₃ solution. That means,

100 g of CoCl₃ solution 19.6 g CoCl₃ salt.

But Actual mass of CoCl₃ solution = 208.2 g.

Hence we write relationship,

If,   100 g of CoCl₃ solution 19.6 g CoCl₃ salt.

Then, 208.2 g of CoCl₃ solution say 'A' g CoCl₃ salt.

On cross multiplication,

A x 100 = 19.6 x 208.2

A = 40.80 g

Mass of CoCl₃ salt = 40.80 g.

Molar mass of CoCl₃ salt =165.87 g/mol

Then # of moles are calculated as,

# of moles of CoCl₃ = Mass of CoCl₃ / Molar mass of CoCl₃.

= 40.80 / 165..87

= 0.246 moles.

There are 0.246 moles of CoCl_3.