Calculate the molarity of each of the following solutions: (a) 30 g of Co(NO3)2.6H2O in 4.3 L of solution (b) 30 mL of 0.5 M H2SO4 diluted to 500 mL.

Calculate the molarity of each of the following solutions: (a) 30 g of Co(NO₃)₂.6H₂O  in 4.3 L of solution (b) 30 mL of 0.5 M H₂SO₄ diluted to 500 mL.

Solution

(a)

Given that mass of Co (NO₃)₂.6H₂O  = 30 g

Volume of solution = 4.3 liter

Molar mass of Co(NO₃)₂.6H₂O = 59 + 2(14 + 3 × 16) + 6 (16 +1 × 2) = 291 g mol⁻¹

Use the formula 

Moles of Co(NO₃)₂.6H₂O = 30/291 = 0.103 mol

Use the formula 

Molarity of Co(NO₃)₂.6H₂O = 0.103/4.3= 0.023 M

(b)

Given that

Volume of H2SO4 (V₁) = 30 ml)

Diluted volume of H2SO4 (V₂) = 500 ml

Number of moles present in 1000 mL of 0.5 M H2SO4 = 0.5 mol

Initial molarity M₁= 0.5 M 

We have to find M₂

Use the formula

M₂V₂ = M₁V₁

plug the values we get

M₂  × 500  = 0.5 × 30

M₂ = 15/ 500 = 0.03 M