OneMondaymorningPaulandhisclassmateswereinsciencelaboratoryfortheirpracticalchemistrylesson.Thestudentsweregoingtoworkinpairstodoanexperiment.Beforetheybegantheteachergavethemthisdescriptionofthedifferentstagesoftheexperiment.

Stage1:Preparetheequipment:atesttubeacrucibleaBunsenburnerandtongs.

Stage2:Weigh5gramsofbakingsoda(sodiumbicarbonate)andputitinacrucible.

Stage3:Heat10mlofhydrochloricacid(盐酸)inatesttube.

Stage4:Pourthewarmacidontothebakingsodaandcontinuetoheatthemixture.

Result:Theacidreactswiththebicarbonate（碳酸氢盐）toformwatercarbondioxidegasandsalt.Thehotterthemixturethequickerthereaction.Continuetoheatthemixtureuntilthewaterevaporatesleavingthesaltinthecrucible.

Paulandhispartnerfollowedtheinstructionsandsetuptheirequipment.Paulwenttothecupboardtogetabottleofhydrochloricacid.Hefoundthattherewasonlyonebottleinthecupboardsohetookthat.TherewasnolabelonthebottleandPauldidn’tcheckwiththeteacherifitwastherightsolution.

Hemeasuredtheliquidandpoureditintoatesttube.UsingtongstoholdthetesttubeheheateditovertheBunsenburner.That’swhenthingsstartedtogowrong.Theliquidinthetesttubewasnothydrochloricacid.Whenitwasheateditformedathickcloudofwhitegas.Soontheroomwasfullofthisstrongsmellingwhitegas.

Allthestudentsstartedcoughingandtheireyeshurt.Theteacherimmediatelyopenedthewindowsandorderedthestudentstoleavethelaboratoryatonce.Sherealizedthattheliquidwasacrylamide(丙烯酰胺)andthatitispoisonous.

Fortunatelynobodywasinjuredintheincident.Howeverittaughtthestudentsandtheteacheragoodlesson.

【小题1】Whatlessondidtheincidentteachthestudentsandtheteacher?

A．Neverhaveabottlewithoutalabelinthechemistrylab!B．Obeyyourteacher’sinstructionsintheChemistrylab.C．Acrylamidecan’ttaketheplaceofhydrochloricacid.D．Findingsomethingunusualhappenedyouhavetoleavethelaboratoryatonce.【小题2】Whatsubstancewerethestudent