Water of Crystallisation

How many molecules of water are there per unit of aluminum hydroxide in Al(OH)₃.3H₂O?

• 1

• 2

• 3

• There is not enough information to know

Tags

NGSS.MS-PS1-1

What name is given to a crystal that does not contain any water of crystallization?

• Dry

• Hydrated

• Insoluble

• Anhydrous

What name is given to a crystal that contains water of crystallization?

• Wet

• Hydrated

• Soluble

• Aqueous

What is the correct chemical formula for a compound of zinc sulfate containing 7 moles of water of crystallisation?

• ZnSO₄.7H₂O

• ZnSO₄ + 7H₂O

• ZnSO₄ : 7H₂O

• ZnSO₄(7H₂O)

Which of the following statements best defines water of crystallization?

• The arrangement of water molecules around an ion.

• The amount of increase in size of a crystal when added to water.

• Molecules of water that are present in the lattice of a crystal.

• The minimum amount of water needed to completely dissolve a crystal.

In an experiment, 10 g of red CoCl₂·6H₂O is heated in a crucible. After a while, the sample turns violet, and a mass of 6.97 g is recorded. Further heating produces a blue powder of anhydrous CoCl₂ and a constant mass of 5.46 g is recorded. Which of the following statements may explain why the sample initially turns violet?

• During heating, only some of the hydrated water molecules are removed, producing a different hydrated compound but with fewer water molecules.

• During heating, CoCl₂·6H₂O reacts with oxygen in the air to produce CoO, which is a violet solid.

• During heating, there is an increase in the number of hydrated water molecules, producing a different hydrated compound but with more water molecules.

• Until the sample is heated to constant mass and only the blue CoCl₂ remains there is a mixture of both the blue and red forms, which appears a violet colour.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

NGSS.MS-PS1-5