Question

Joan’s initial nickel (II) chloride sample was green and weighed 4.3872 g. After the dehydration reaction and removal of excess thionyl chloride, the residue was yellow, and had a mass of 2.3921 g.
(a) Was the nickel chloride sample a hydrate? ___________________
(b) If the data indicates a hydrate, calculate x, the number of waters of hydration.
Show your work.

Answer 1

Answer:

a) yes, it was an hydrate

b) the number of waters of hydration, x = 6

Explanation:

a) yes it was an hydrate because the mass decreased after the process of dehydration which means removal of water thus some water molecules were present in the sample.

b) NiCl2. xH2O

mass if dehydrated NiCl2 = 2.3921 grams

mass of water in the hydrated sample = mass of hydrated - mass of dehydrated = 4.3872 - 2.3921 = 1.9951 g which represent the mass of water that was present in the hydrated sample.

NiCl2.xH2O

mole of dehydrated NiCl2 = m/Mm = 2.3921/129.5994 = 0.01846 mole

mole of water = m/Mm = 1.9951/18.02 = 0.11072 mole

Divide both by the smallest number of mole (which is for NiCl2) to find the coefficient of each

for NiCl2 = 0.01846/0.01846 = 1

for H2O = 0.11072/0.01846 = 5.9976 = 6

thus the hydrated sample was NiCl2. 6H2O