2024 Prelims NJC H2 Chem P2 (Ans)

[Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on Question Paper. Additional Materials: Data Booklet 9729/02 23 August 2024 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /9 2 /22 3 /6 4 /7 5 /14 6 /17 Paper 2 Total /75 Marks Weightings Paper 1 /30 15% Paper 2 /75 30% Overall Percentage Paper 3 /80 35% Paper 4 /55 20% Grade This document consists of 19 printed pages and 1 blank page.

NJC/H2 Chem Preliminary Examination/02/2024 2 Answer all the questions in the spaces provided. 1 (a) Element A is from Period 4 of the Periodic Table. The first eight ionisation energies of element A, in kJ mol-1, are 947 1798 2735 4837 6043 12310 14300 16800 (i) Identify element A and explain your answer. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… [2] (ii) Explain the difference between the first ionisation energy of element A compared to the element to its right on the Periodic Table. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… [2] Element A is Arsenic. There is a large difference between the 5th and 6th ionisation energies of A. The 6th electron is from an inner electronic shell. A has 5 valence electrons, hence it is from Group 15. The element to the right is Selenium. 1st ionisation energy of Se involves the removal of paired 4p electrons which experiences inter-electronic repulsion. Less energy is needed to remove the electron from Se than the unpaired 4p electron in A. Hence, the IE of Se is lower.

NJC/H2 Chem Preliminary Examination/02/2024 3 [Turn over (b) In organic chemistry, an aldol is a structure consisting of a hydroxy group ( -OH) two carbons away from either an aldehyde or a ketone. Aldols are the product of a carbon -carbon bond-formation reaction, giving them wide applicability as a precursor for a variety of other compounds. (i) Give the IUPAC name of the structure below: O HO Cl IUPAC name: ………………………………. [1] (ii) The compound above undergoes elimination to form the following product: CH(OH)CHCHO. Give the reagents and conditions f