0620/42Cambridge IGCSE-Mark SchemeMarch 2023First ProofCambridge International General Certificate of Secondary EducationIGCSECHEMISTRY0620/42Paper 4 Theory (Extended)February/March 2023MARK SCHEMEMaximum Mark 80Page 1 of 80620/42Cambridge IGCSE-Mark SchemeMarch 2023First ProofQuestionAnswerMarksGuidance1aM1 Carbon dioxide /CO211b78(%)1cCalcium oxideA CaCO3/limestone?(CaCO3 slurry also usedin desulfurisation).1dCatalytic converter11eiLowest MrI'lightest gas'Check latest MS (Mar 2021?)1fToxic1A'kills you'etc1gM1 OxygenA sugar or carbohydrate?M2 Glucose21hM1 2 dot and cross double bonds2 pairs of non-bonding e on O and 0 non-bonding e on C2A four individual non-bonding e11Page 2 of 80620/42Cambridge IGCSE -Mark SchemeMarch 2023First ProofQuestionAnswerMarksGuidance2aMetallic2biLighted splint and(squeaky)pop1R Glowing splint2bi141A range?2biiiUniversal indicator /pH paperR indicators such as litmus/thymolphthalein?2biv2Na(s)+H2O(l)2NaOH(aq)+H2(g)M1 NaOH as a productM2 correct equationM3 state symbols32ci2cii6Liprotons33neutrons34electrons32Each row√3M1(10×6)+(90×7)=690M1 use of abundance x massM2690/10=6.9M2 mass of average atom to one dp26.92civM1 Both K with new octet of dots3Page 3 of 8