CCEA A-Level Chemistry 1110
Formulae, Equations and Amounts of Substance
Atomic Structure
Bonding
Intermolecular Forces and Structure
Shapes of Molecules and Ions
Redox
The Halogens
Acid-Base Titrations
Qualitative Tests
Formulae and Amounts of a Substance
Nomenclature and Isomerism in Organic Chemistry
Alkanes
Alkenes
Halogenoalkanes
Alcohols
Infrared Spectroscopy
Energetics
Kinetics
Equilibrium
Group II Elements and Their Compounds
Lattice Enthalpy, Entropy and Free Energy
Rates of Reaction
Equilibrium and Acid-Base Equilibria
Isomerism
Aldehydes and Ketones
Carboxylic Acids
Derivatives of Carboxylic Acids
Aromatic Chemistry
Spectroscopy and Chromatography
Volumetric Analysis
Transition Metals
Electrode Potentials
Amines
Amides and Polymers
Amino Acids and Proteins
Formulae, Equations and Amounts of Substance
Hydrated salts and water of crystallisation
- 3 things to know
- Unit AS 1
Overview
Term water of crystallisation, anhydrous compound and colour change seen when hydrated copper(II) sulfate is heated strongly.
What you need to know
Answer each one before you reveal it.
Define the term water of crystallisation.
What is meant by an anhydrous compound?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Define the term water of crystallisation.
Model answer
Water of crystallisation is water that is chemically bound into the crystal structure of a salt in a fixed molar proportion.
- 2
What is meant by an anhydrous compound?
Model answer
An anhydrous compound is one that contains no water of crystallisation.
- 3
What does it mean to describe a salt as hydrated?
Model answer
A hydrated salt is one whose crystals contain water of crystallisation as part of their structure.
- 4
How is water of crystallisation shown in the formula of a salt?
Model answer
It is written after the formula of the salt separated by a dot, as in CuSO₄·5H₂O, where the number gives the moles of water per mole of salt.
- 5
Describe the colour change seen when hydrated copper(II) sulfate is heated strongly.
Model answer
The blue hydrated crystals turn white as the anhydrous copper(II) sulfate is formed and the water is driven off.
- 6
Why is a hydrated salt heated to constant mass rather than for a fixed time?
Model answer
Heating until two successive weighings agree shows that all the water of crystallisation has been driven off and no more mass can be lost.
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