2021 SASS 4E Chem MYE Error Analysis Ans

STANDREW’SSECONDARYSCHOOL CHEMISTRY 6092 Mid-YearExamination2021Error Analysis ANSWERS ANSWERS 1 2 3 4 5 6 7 8 9 10D B B C C A C D D C11 12 13 14 15 16 17 18 19 20A C D B D C D B B C21 22 23 24 25D D B C C Q Answer Remarks1 D Allatomsofaparticularelementwillalwayshave:● Thesameatomicnumber● Thesamenumberofproton(s)presentinthenucleus● Thesamenumberofelectron(s)● Thesameelectronicconfiguration● Thesamechemicalproperties Nitrogenconsistsoftwoisotopes (nitrogen −14)and (nitrogen −15),which714𝑁 715𝑁areNatomsthatdifferinmassnumbers. (ps: This is only applicable to elementswithmorethan1isotope. Eg: Phosphoroushasonly1isotope 31 P (phosphorous −31). Hence, all phosphorous atoms will have the same massnumber.) 2 B Isotopesareatomsofthesameelementwithsamenumberofprotonsbutdifferentnumberofneutrons. Pisanatom(particlewithnocharge:no.ofelectrons=no.ofprotons).With8e − , Phas8protons. Theisotopeof Pwillbetheparticlethatalsocontains8protons.Q + ionhas10electrons Qatomhas10+1=11electrons(Qatomloses1electrontoformQ + )⇒Qatomhas11protons.(✘ ) R 2 − ionhas10electrons Ratomhas10 −2=8electrons (Ratomgains2electronstoformR 2 − )⇒Ratomhas8protons.(✓) _______________________________________________________________________________________________________________________________________________________________________________________ Page1

Satomhas18electrons⇒Satomhas18protons.(✘ )3 B Eachsinglecovalentbondcontains1pairofelectronssharedbetween1pairofatoms.Toformasinglecovalentbond,eachatomshares1ofitsvalenceelectron. P=GroupVelement=5valenceelectrons (P shares 3 (eg. PH3 ) or 5 (eg. P4 O10 ) valenceelectronstoformcovalent bonds) Fromthediagram,eachPatomformed5covalentbondsbysharingall5valenceelectrons. Xforms3covalentbonds=shares3ofitsvalenceelectrons=GroupIIIor VelementYforms1covalentbond=shares1ofitsvalenceelectrons=Group VIIelementorhydrogen4 C ● XYisasalt.Saltsareioniccompoundscomposedofacation(frommetalorNH4 + )andananion(fromacid).● IonsinXYformacrystal latticestructurethatareheldinafixedandregulararrangement. Ioniccompoundsarenotabletoconductelectricityinthesolidstateastheionsareintheirfixedpositions(latticestructure). SinceXYisabinarycompound,theratioofX + toY − is1:1.5 C Forthisseriesofreactions:excessreactant –theacids(CH3 COOH,HCl,H2 SO4 )limitingreactant –Na2 CO3 All3reactionswillgivethesamevolumeofgas(CO2 )produced. CH3 COOH:Weakacid(partiallyionisesinsolution),monobasic ⇒ slowestreactionHCl :Strongacid(completelyionisesinsolution),monobasicH2 SO4 :Strongacid(completelyionisesinsolution),dibasic⇒fastestreaction6 A Propertiesofsimplecovalentcompounds:● Lowmeltingandboilingpoints● Doesnotconductelectricity● Insolubleinwater;Solubleinorganicsolvents7 C Massofcalcium= ×14.0g=12.5g 4056 %Calciuminthebone= ×100%=20% 12.550 8 D Hydrocarbonsarecompoundsthatcontainhydrogenandcarbononly.Cm Hn +O2 →mCO2 +(n/2)H2 O Moleratioofhydrocarbon:CO2 1:m5:30m=69 D H2 SO4 +2NaOH→Na2 SO4 +2H2 O MolesofH2 SO4 =1×0.03=0.03mol ____________________________________________________________