2024 Prelims NJC H2 Chem P2 (QP)

[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]

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 for the reaction. ……………………………………………………………………...………………………… [1] (iii) State the isomerism which the product displays. ……………………………………………………………………...………………………… [1] (iv) With the use of a diagram, explain why the cis isomer is formed preferentially. ……………………………………………………………………...………………………… ……………………………………………………………………...………………………… ……………………………………………………………………...………………………… [2] [Total:9]

NJC/H2 Chem Preliminary Examination/02/2024 4 2 (a) Some information about NO3− and NO2− are provided in Table 2.1 and Table 2.2 Table 2.1 Electron arrangement around N in NO3− 3 bond pairs & 0 lone pair Electron arrangement around N in NO2− 2 bond pairs & 1 lone pair Table 2.2 Nitrogen−oxygen bond in NO3− 0.124 nm Theoretical N−O bond length 0.136nm Theoretical N=O bond length 0.115nm Fig. 2.1 shows a possible structure of NO3− . N O O O Fig.2.1 (i) Use relevant information from the above tables to explain why Fig. 2.1 does not represent an accurate model for the bonding in NO3− . ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. [1] (ii) Nitrogen atoms undergo the same type of hybridisation as carbon atoms do. Suggest the mixing and overlap of atomic orbitals which accounts for the N−O bond length in NO3− . ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. [3]

NJC/H2 Chem Preliminary Examination/02/2024 5 [Turn over (iii) The bond angle around nitrogen in NO3− and NO2− are different. Use VSEPR theory to explain how the bond angle in NO3− is different from that in NO2− . ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. [2] (b) When solid magnesium nitrate is heated, it decomposes to give magnesium oxide, oxygen and nitrogen dioxide gas. (i) Write an equation for the decomposition of solid magnesium nitrate. ……………………………………………………………………...…………………….. [1] (ii) Zinc nitrate decomposes in the same way as magnesium nitrate when it is heated. Use data from the Data Booklet to explain the difference in decomposition temperature between zinc nitrate and magnesium nitrate. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. ……………………………………………………………………...…………………….. [3]

NJC/H2 Chem Preliminary Examination/02/2024 6 (c) Magnesium and beryllium are Group 2 elements, but beryllium behaves differently from that of magnesium. There is said to be a ‘diagonal relationship’ between beryllium and aluminium as they show similar chemical behaviour due to their similarities in electronegativity and charge density. (i) Draw the dot-and-cross diagram to show the bonding in BeCl2. [1] (ii) When a few drops of water are added to solid beryllium chloride, steamy white fumes are evolved and a white solid remains, which is insoluble in water. Write a balanced equation for this reaction. ……………………………………………………………………...……………………... [1] (iii) At 750 C, the relative molecular mass of gaseous beryllium chloride corresponds to the formula BeCl2. At 550 C, gaseous beryllium chloride exists as a mixture of BeCl2 and Y (relative molecular mass of Y is 160). (I) Suggest the structure of Y, showing any dative bonding. [1] (II) Determine the relative ratio of BeCl2 and Y in a gaseous sample at 550 C which has a relative molecular mass of 100. [1]

NJC/H2 Chem Preliminary Examination/02/2024 7 [Turn over (d) Magnalium is an alloy of aluminium and magnesium which is used in boat -building. The diagram below shows some reactions of magnalium. Identify A, B and C. A: ……………………………… B: ……………………………… C: ……………………………… [2] colourless solution HCl(aq) excess NaOH(aq) white ppt white residue, A colourless filtrate, B a few drops of HCl(aq) white solid, C filter sample of magnalium

NJC/H2 Chem Preliminary Examination/02/2024 8 (e) Grignard reagents, RMgX, can be prepared by the reaction of magnesium with halogenoalkane, RX, using dry ether as the solvent. A Grignard reaction occurs when a Grignard reagent is reacted with a carbonyl compound to prepare alcohols in a two -step reaction. An example of a Grignard reaction is shown below. CH3CH2MgBr CH3 C O H CH3CH CH2CH3 O MgBr+ CH3CH CH2CH3 OH Mg(OH)Br Step I Step II Grignard reagent (i) What type of reaction takes place in steps I and II? Step I: …………………………………………………………………………… Step II: ………………………………………………………………………….. [2] (ii) Step I of the above Grignard reaction is known to proceed via the following two