Question

a hydrate of cobalt (II) nitrate has the following formula: Co(No3)2 X xH2O. the water in a 3.41g sample of the hydrate was driven off by heating. the remaining sample had a mass of 2.14 g. Find the number of waters of hydration in the hydrate

Answer 1

given that mass of hydrate of cobalt (II) nitrate= 3.41 g

mass of cobalt (II) nitrate= 2.14 g

thus mass of water present = 3.41-2.14 = 1.27 g

number of moles = amount in g / molar mass

number of moles of water = 1.27 g/18.02 g/ mole = 0.0704 mole

mole of cobalt (II) nitrate=2.14 g/ 182.943 g/mol= 0.0117 mole

now calculate the mole ratio by dividing small value

H2O : 0.0704 /0.0117= 6

cobalt (II) nitrate: 0.0117/0.0117= 1

Hence x= 6 ,

Co(No3)2 .6H2O

There are 6 moles of waters of hydration in the hydrate