Question

A 1.167 grams sample of hydrated Nickel (II) Chloride is heated until a constant mass is achieved. The constant mass of the sample is .750 grams. What is the formula and name of the hydrate?

Answer 1

Answer:

NiCl₂·4H₂O, its name being nickel (II) chloride tetrahydrate.

Explanation:

The constant mass achieved after heating is the mass of anhydrous nickel (II) chloride, NiCl₂. While the mass lost was water.

• Mass lost = 1.167 g - 0.750 g = 0.417 g

Now we convert 0.750 g of NiCl₂ into moles, using its molar mass:

• 0.750 g NiCl₂ ÷ 129.6 g/mol = 0.0058 mol NiCl₂

Then we convert 0.417 g of H₂O into moles:

• 0.417 g H₂O ÷ 18 g/mol = 0.0231 mol H₂O

With the above information we can calculate that the number of H₂O moles is 4 times higher than the number of NiCl₂ moles.

Meaning that the formula of the hydrate is NiCl₂·4H₂O, its name being nickel (II) chloride tetrahydrate.