Lesson Worksheet: Water of Crystallization Chemistry

In this worksheet, we will practice defining water of crystallization and explaining its effect on the structures, stabilities, and properties of crystals.

Q1:

How many molecules of water are there per unit of aluminum hydroxide in Al(OH)·3HO32?

Q2:

The diagram below shows a piece of equipment called a desiccator that is used to keep substances in a dry atmosphere. Why is the bottom of the desiccator lined with anhydrous calcium chloride?

  • ACalcium chloride is very efflorescent and will easily keep the air inside the desiccator moist.
  • BCalcium chloride is very hygroscopic and will easily remove any moisture from the air inside the desiccator.
  • CCalcium chloride is very good at absorbing carbon dioxide from the air inside the desiccator.
  • DCalcium chloride is inert and will not react with the sample in the desiccator.
  • ECalcium chloride ensures the pH is kept neutral.

Q3:

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

  • AInert
  • BDry
  • CHydrated
  • DInsoluble
  • EAnhydrous

Q4:

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

  • AAnhydrous
  • BWet
  • CAqueous
  • DHydrated
  • ESoluble

Q5:

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

  • AZnSO7HO42×
  • BZnSO+7HO42
  • CZnSO7HO42
  • DZnSO·7HO42
  • E(ZnSO)(7HO)42

Q6:

The diagram below shows a small portion of a hydrated crystal and how the water molecules interact with the ions in it. Why are the oxygen atoms interacting with the positive ions and the hydrogen atoms interacting with the negative ions in water?

OHH+OHH+OHH
  • AThe hydrogen atom has fewer electrons than the oxygen atom and so it is attracted to the ion with more electrons.
  • BIn a molecule of water, the oxygen atom has a partial negative charge and so it is attracted to positive ions, and the hydrogen atoms have a partial positive charge and so they are attracted to negative ions.
  • CThe oxygen atom has more electrons than the hydrogen atom and so it is attracted to the ion with fewer electrons.
  • DIn a molecule of water, the oxygen atom has a partial positive charge and so it is attracted to negative ions, and the hydrogen atoms have a partial negative charge and so they are attracted to positive ions.

Q7:

Methane hydrates are solid compounds that contain molecules of methane trapped within the crystal structure of water, as shown in the image below.

If the chemical formula for a methane hydrate is 4CH·23HO42, how many moles of water are there per mole of methane?

Large quantities of methane hydrates are found in cold oceans and regions of permafrost. Why might rising global temperatures and their effects on methane hydrates be of concern?

  • ARising global temperatures could result in the decomposition of methane hydrates and the release of methane, a greenhouse gas.
  • BRising global temperatures could result in the reaction of water of methane to methanoic acid, increasing the acidity of the oceans.
  • CRising global temperatures could result in the decomposition of methane hydrates and the release of hydroxide ions, a greenhouse gas.
  • DRising global temperatures could result in the combustion of methane hydrates releasing oxygen and hydrogen into the atmosphere.
  • ERising global temperatures could result in an increase in the formation of methane hydrates, trapping more methane, a greenhouse gas.

Q8:

Which of the following statements best defines water of crystallization?

  • AThe heat released during crystallization.
  • BThe arrangement of water molecules around an ion.
  • CThe amount of increase in size of a crystal when added to water.
  • DMolecules of water that are present in the lattice of a crystal.
  • EThe minimum amount of water needed to completely dissolve a crystal.

Q9:

In an experiment, 10 g of red CoCl·6HO22 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 of CoCl·6HO22 initially turns violet?

  • ADuring heating, only some of the hydrated water molecules are removed, producing a different hydrated compound but with fewer water molecules.
  • BDuring heating, chlorine gas is produced, leaving a solid compound of Co(OH)2, which is violet in color.
  • CThe compound CoCl·6HO22 is light sensitive and in the presence of sunlight rapidly decomposes to form elemental cobalt.
  • DDuring heating, CoCl·6HO22 reacts with oxygen in the air to produce CoO, a violet solid.
  • EDuring heating, there is an increase in the number of hydrated water molecules, producing a different hydrated compound but with more water molecules.

What is the formula for the violet cobalt sample?

  • ACoCl·HO22
  • BCoCl·3HO22
  • CCoCl·5HO22
  • DCoCl·4HO22
  • ECoCl·2HO22

When added to excess water, the sample of blue CoCl2 returns to the original red color of CoCl·6HO22. Which of the following equations correctly describes this reaction?

  • ACoCl()+2HO()CoCl·2HO()2222sls
  • BCoCl()+6HO()CoCl·6HO()sls22
  • CCoCl()+6HO()CoCl·6HO()2222sls
  • DCoCl()+6HO()CoCl+6HO()2222sls
  • ECoCl()+6HO()CoCl·6HO()2222lgl

Q10:

When exposed to Moist air, zinc(II) chloride will readily absorb water to form hydrates, as shown in the equation below: ZnClZnCl·2HO222Moistair What term is given to a substance that can remove moisture from the air?

  • ADrier
  • BSponge
  • CHydrophilic
  • DHygroscopic
  • ECrystallic

This lesson includes 5 additional questions for subscribers.

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