Molality of 0.8 M H₂SO₄ solution (density 1.06 g cm⁻³) is _______

Molality from Molarity | Density Based Numerical | JEE Mains PYQ

Q. Molality of 0.8 M H₂SO₄ solution (density 1.06 g cm⁻³) is ________ × 10⁻³ m.

Explanation

Step 1: Take 1 litre of solution

Molarity = 0.8 M ⇒ moles of H₂SO₄ = 0.8 mol

Step 2: Calculate mass of solution

Density = 1.06 g mL⁻¹
Mass of 1 L solution = 1.06 × 1000 = 1060 g

Step 3: Calculate mass of solute

Molar mass of H₂SO₄ = 98 g mol⁻¹
Mass of solute = 0.8 × 98 = 78.4 g

Step 4: Calculate mass of solvent

Mass of solvent = 1060 − 78.4 = 981.6 g = 0.9816 kg

Step 5: Calculate molality

Molality (m) = moles of solute / kg of solvent
m = 0.8 / 0.9816 = 0.815 m

Molality = 815 × 10⁻³ m

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