chemsitry 2 question

Question

how many moles of solid magnesium chloride is required to mix with 15 mol of water to produce an aqueous solution with a magnisium chloride molarity of 0.36 m? the molar mass of MgCl2 is 95.21g/mol. the molar mass of water is 18.02 g/mol

Answer 1

Magnesium chloride = MgCl₂

0.36 molal MgCl₂ = 0.36 moles MgCl₂ in 1 kg water

How many kg of water do we have? We have 15 mol H₂O x 18 g/mol = 270 g = 0.270 kg H₂O

How many moles MgCl₂ do we need? We need 0.36 mol/kg x 0.270 kg = 0.0972 moles MgCl₂

Mass MgCl₂ needed = 0.0972 mol MgCl₂ x 95.21 g/mol = 9.25 g = 9.3 g MgCl₂ needed (2 sig. figs.)