THE CHEMISTRY OF CRYSTALS
Manysubstances have a crystallineform, especially salts (see page 70). A
crystalis a solid piece ofmattercomposedofmanyatomsarrangedin specific
patterns.Each crystallinesubstancehas its own crystalpattern,justas each
personhas his ownfingerprintsand no one else's.Crystalsof any givenchemical
may vary in size,butthearrangementoftheatomswithinthe crystals doesnot
vary.Whenmanycrystalsofa substanceaccumulate,the samepatternrepeats
itselfover and over, with only slightvariationsdependingon the size andpurity
ofthe crystal. Snowflakes, which are melting ice crystals, have a 6-sided, or
hexagonalpattern.The smaller crystalsthatbandtogethertomakeup a large
snowflake are all 6-sided figures, too.
Sometimes crystalsincludemoleculesofwateralongwiththeirownatoms.
Thewatermolecules affect theappearanceofthecrystalbutnotitschemical
characteristics.In itsordinarycrystallineform, coppersulfatecontainswater
molecules and has a lovely bluecolor.When dissolved in aliquid,these crystals
form asolutionofthe same blue color.Ifthe bluecrystallineform isheated,
however, orcrushedintoa powder,it loses thewatermolecules and becomes
white. Nevertheless, it still has all ofthe same chemical properties it had
before.
Watermolecules, whenincludedin crystals, make upwaterofcrystallization,
also calledwaterofhydration. (All crystals arenotcapableofincludingwater
molecules.) When crystals lose waterofcrystallizationthroughevaporation,
the process is called efflorescence.When crystals absorbwaterfrom the air,
the process is calleddeliquescence.The followingexperimentswill show you the
effectsofefflorescence and deliquescence.
HOW YOU CAN DETECT WATER OF HYDRATION
Gather these materials:Coppersulfatecrystals (CUS04);sodiumcarbonate
crystals(Na2COa) ;2 testtubes;analcoholburner;a fewdropsofwater;and
paperand pencil.
Follow this procedure: Write down adescriptionofthe appearanceofeach
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