Question

if density of 3M NaCl solution is 1.25g/ml. then what is molelity of it?

Answer 1

#79998 Chemistry, Other

If density of 3 M NaCl solution is 1.25 g/ml, then what is molality of it?

**Answer:**

3 Molar solution means there are 3 moles of NaCl in 1 L.

M (Na Cl) = 58.44 g/mole

In 1 liter of water there is: m (NaCl) = 3 x 58.44 = 175.32 g.

$\rho = \mathrm{m} / \mathrm{V}$

Mass of 1 liter of solution = 1.25 g/ml x 1000 ml = 1,250 g

$m_{\text{solution}} = m_{\text{solvent}} + m_{\text{solute}}$

m (H₂O) = 1,250 – 175,32 = 1,074.68 g

So 1,074.68 ml or 1,074.68 g of water is mixed with 3 moles of NaCl to make the 3 M solution.

Molality = mass of solute in number of moles / mass of solvent in kg

Cm (NaCl) = 3 / 1.07 kg = 2.79 m