Question

The concentration of Mg2+ in seawater is about 0.055 M. (a) How many liters of seawater will produce 1.00 kg of magnesium. (b) How many kilograms of calcium oxide, CaO, must be added to the seawater sample of part (a) in order to precipitate all of Mg2+ as magnesium hydroxide. (c) Write a balanced equation for reaction that involves Mg2+(aq), CaO(s), and H2O to produce Mg(OH)2(s).

Answer 1

Molarity of Mg+2= 0.055 M = 0.055 moles/liter

moles of Mg in liter of Mg+2 =0.055 , atomic weight of Mg= 24

moles= mass/ atomic weight

mass of Mg= 0.055*24 gm =1.32 gm of Mg are there in 1 L of sea water

1 kg =1000 gm are there in 1000*1/1.32 L of sea water = 757.6 Liters of sea water

Mg+2+ H2O+ CaO ----------> Mg(OH)2+ Ca+2

1 mole of Mg+2 requires 1 mole of CaO for complete precipitation as Mg(OH)2 ( molar mass of CaO= 56 g/mole)

24 gm of Mg+2 requires 56 gm of CaO for complete precipitation

1000 gm of Mg+2 requires 1000*56/24 gm of CaO =2333.3 gm of CaO= 2.333 kg of CaO.