Question

Calculate molarity and molality of solution prepared by mixing equal volume

Answer 1

Assume y ml of each solution, a and b, are mixed

Calculate mass of solution using formula, mass = density(d) × Volume (V)

Mass of solution a, ma = 1.218 × y = 1.218y

Mass H2SO4, msolute a = 30% or 30×1.218y100

msolute a = 0.3654y g

Moles H2SO4, nsolute a = 0;3654y98or 0.003729y mol (Using formula, moles = mass, m /Molar mass)

Mass of water, msolvent a = mA- msolute a

msolvent a = 1.281y – 0.3654y

msolvent a= = 0.8526y g or 0.8526 X 10-3y kg

Similarly for solution B

mb = 1.610y g

msolute b = 70×1.610y100or 1.127y g

nsolute b = 1.127y98 or 11.5y mol

msolvent b = 1.610y – 1.127y = 0.483y g or 0.483 × 10-3y kg

When y ml of each solution is mixed

Total volume, V = y + y = 2y ml or 2y × 10-3 L

Total moles of H2SO4, nsolute = nsolute a + nsolute b

nsolute= 0.003729y + 11.5y = 0.015229y mol

Total mass of solvent in kg, msolvent = msolvent a + msolvent b

msolvent = 1.3356y×10-3 kg

Molarity, M =nsolute/V

M = 0.015229y2y×10−3

M = 7.614M

Molality, m = nsolutemsolvent in kg=0.015229y1.3356y×10−3=11.402m