What mass of NaOH is required to prepare a 0.25 m aqueous solution using 400 g of water?

Step-by-step solution

Molality ( m ) is defined as the number of moles of solute per kilogram of solvent. Given: Molality ( m ) = 0.25 mol kg ⁻¹ Mass of solvent (water) = 400 g = 0.4 kg Molar mass of NaOH = 23 + 16 + 1 = 40 g mol ⁻¹ Using the formula for molality: m = Moles of solute Mass of solvent in kg Moles of NaOH required = m Mass of solvent in kg Moles of NaOH = 0.25 0.4 = 0.1 mol Mass of NaOH = Moles Molar mass Mass of NaOH = 0.1 mol 40 g mol ⁻¹ = 4 g . Answer: 4 g