hydrate | Description, Formation, & Examples | Britannica

Hydrate, any compound containing water in the form of H2O molecules, usually, but not always, with a definite content of water by weight. hydrate Sections&Media Article Introduction FastFacts RelatedContent Media Images AdditionalInfo AdditionalReading MoreArticlesOnThisTopic Contributors ArticleHistory Home Science Chemistry hydrate chemicalcompound Print Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/hydrate More GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). FeedbackType Selectatype(Required) FactualCorrection Spelling/GrammarCorrection LinkCorrection AdditionalInformation Other YourFeedback SubmitFeedback Thankyouforyourfeedback Oureditorswillreviewwhatyou’vesubmittedanddeterminewhethertorevisethearticle. JoinBritannica'sPublishingPartnerProgramandourcommunityofexpertstogainaglobalaudienceforyourwork! ExternalWebsites SantaMonicaCollege-PropertiesofHydrates BritannicaWebsites ArticlesfromBritannicaEncyclopediasforelementaryandhighschoolstudents. hydrate-StudentEncyclopedia(Ages11andup) By GeorgeB.Kauffman | ViewEditHistory zeolite;hydrate Seeallmedia RelatedTopics: deliquescence aluminumchlorohydrate gashydrate calciumsilicatehydrate hydration ...(Showmore) Seeallrelatedcontent→ hydrate,anycompoundcontainingwaterintheformofH2Omolecules,usually,butnotalways,withadefinitecontentofwaterbyweight.Thebest-knownhydratesarecrystallinesolidsthatlosetheirfundamentalstructuresuponremovaloftheboundwater.Exceptionstothisarethezeolites(aluminumsilicatemineralsortheirsyntheticanaloguesthatcontainwaterinindefiniteamounts)aswellassimilarclayminerals,certainclays,andmetallicoxides,whichhavevariableproportionsofwaterintheirhydratedforms;zeolitesloseandregainwaterreversiblywithlittleornochangeinstructure.Substancesthatspontaneouslyabsorbwaterfromtheairtoformhydratesareknownashygroscopicordeliquescent,whereashydratesthatloseso-calledwaterofhydrationorwaterofcrystallizationtoformtheunhydrated(anhydrous)substancesareknownasefflorescent.Inmanycases,theuptakeandlossofwater(byheating,decreasingpressure,orothermeans)arereversibleprocesses,sometimesaccompaniedbychangesincolour.Forexample,bluevitriol,orcoppersulfatepentahydrate(CuSO4∙5H2O),isblue,coppersulfatetrihydrate(CuSO4∙3H2O)isblue,andanhydrouscoppersulfate(CuSO4)iswhite. BritannicaQuiz Science:FactorFiction? Doyougetfiredupaboutphysics?Giddyaboutgeology?Sortoutsciencefactfromfictionwiththesequestions. OtherexamplesofhydratesareGlauber’ssalt(sodiumsulfatedecahydrate,Na2SO4∙10H2O);washingsoda(sodiumcarbonatedecahydrate,Na2CO3∙10H2O);borax(sodiumtetraboratedecahydrate,Na2B4O7∙10H2O);thesulfatesknownasvitriols(e.g.,Epsomsalt,MgSO4∙7H2O);andthedoublesaltsknowncollectivelyasalums(M+2SO4∙M+32(SO4)3∙24H2O,whereM+isamonopositivecation,suchasK+orNH4+,andM3+isatripositivecation,suchasAl3+orCr3+).Inmanycases,hydratesarecoordinationcompounds.CuSO4∙5H2Oisactually[Cu(H2O)4]SO4∙4H2O;fourmoleculesofwaterofhydrationarecoordinatedtothecopperion,whereasthefifthwatermoleculeislinkedtothesulfateion,presumablybyhydrogenbonding.Similarly,MgSO4∙7H2Oisactually[Mg(H2O)6]SO4∙4H2O.X-raydiffractionstudieshaveshownthathydratedberylliumsulfate(BeSO4∙4H2O)andhydratedberylliumnitrate(Be(NO3)2∙4H2O)bothcontainthetetrahedralcomplexion[Be(H2O)4]4+.Anumberofgases—notablythenoblegasesandsimplehydrocarbongasessuchasmethane,ethane,propane,andacetylene,aswellaschlorineandcarbondioxide—formcrystallinehydratescalledclathratecompoundsatrelativelylowtemperaturesandpressures.Clathratecrystalshaveastructureinwhichthewatermoleculesformalooselyheldframeworksurroundingthegasmolecule.Methanehydratesarefoundinlargequantitiesundertheoceanfloorandthepermafrostonland.Itisbelievedthatthereismorefuelinunderseamethanehydratesthanintheworld’scoal,naturalgas,andoilreserves.Therearealsoconcernsthatclimatechangecouldcausethemethanehydratestobreakdownandreleasetheirmethane,whichwouldworsentheproblemofclimatechange,sincemethaneisamore-effectivegreenhousegasthancarbondioxide.Hydrates,specificallyhydratedioniccompounds,arenamedbytheioniccompoundtheycontain,followedbytheword hydrate,whichisprecededbyaprefixthatindicatesthenumberofwatermoleculesthecompoundcontains.GeorgeB.Kauffman