Question

Calculate the molarity of the following Solution :

(a) 30g of Co (NO3)2 . 6H2O in 4.3L of solution.​

Answer 1

Given :

• Mass of Co(NO₃)₂.6H₂O = 30g
• Volume of solution = 4.3 L

To find :

Molarity of solution

Formula used :

• Number of mole = Mass ÷ molar mass
• Molarity = Number of moles ÷ Volume of solution in L

Solution :

First of all we need to find molar mass of Co(NO₃)₂.6H₂O

• Molar mass of Co(NO₃)₂.6H₂O = ( 1 × Atomic mass of Co ) + 2 × [ ( 1 × Atomic mass of N ) + ( 3 × Atomic mass of O ) ] + 6 × [ ( 2 × Atomic mass of H ) + ( 1 × Atomic mass of O ) ]

➝ Molar mass of Co(NO₃)₂.6H₂O = ( 1 × 59 ) + 2× [ (1×14) + (3×16) ] + 6×[ (2×1) + (1×16) ]

➝ Molar mass of Co(NO₃)₂.6H₂O = 59 + 2×[ 14 + 48 ] + 6×[ 2 + 16 ]

➝ Molar mass of Co(NO₃)₂.6H₂O = 59 + (2×62) + (6×18)

➝ Molar mass of Co(NO₃)₂.6H₂O = 59 + 124 + 108

➝ Molar mass of Co(NO₃)₂.6H₂O = 291 g/mol

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• Number of mole of Co(NO₃)₂.6H₂O = mass ÷ molar mass

➝ Number of mole of Co(NO₃)₂.6H₂O = 30g ÷ 291g/mol

➝ Number of mole of Co(NO₃)₂.6H₂O = 0.1 mole

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• Molarity of solution = Number of mole of Co(NO₃)₂.6H₂O ÷ Volume of Solution in L

➝ Molarity of solution = 0.1 mol ÷ 4.3 L

➝ Molarity of solution = 0.023 M

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ANSWER : 0.023 M