2021 VJC Prelim P2 Qns

1  VJC 2021 8873/02/PRELIM/21 [Turn over CANDIDAT E NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS Higher 1 ……………………………………………….………….. …………………………….. CHEMISTRY 8873//02 Paper 2 Structured Questions Candidates answer on the Question Paper. 15 September 2021 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all the questions. Section B Answer one question. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 8 2 / 13 3 / 9 4 / 9 5 / 13 6 / 8 Section B 7 / 8 / 20

2  VJC 2021 8873/02/PRELIM/21 [Turn over Total / 80 This document consists of 28 printed pages and 2 blank pages. Section A Answer all the questions in this section in the spaces provided. 1 (a ) The nth (n = 1, 2, 3, 4 or 5) ionisation energies of consecutive elements Q to Z, with atomic number below 20, are shown in Fig. 1.1. Fig. 1.1 (i) Define the nth ionisation energy of element T. …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . [1] (ii) Element U is identified as Al. State the value of n. …………………………………………………………………………………………….. . [1]

3  VJC 2021 8873/02/PRELIM/21 [Turn over (b ) Aluminium chloride has a wide number of uses in the chemical industry. Anhydrous AlCl3 adopts different structures depending on the temperature and the state it is in. In the liquid state, it exists as the dimer Al2Cl6 while a mixture of monomer and dimer can be found in the gaseous phase. (i) State the type of interactions between two molecules of AlCl3. …………………………………………………………………………………………….. . [1] (ii) Draw a diagram to show the bonding in an Al2Cl6 dimer, and state the bond angle about the Al atom. …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . [2] (c ) Beryllium chloride, BeCl2, has properties similar to those of AlCl3. (i) Explain why BeCl2 behaves similarly to AlCl3. …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . [1] (ii) BeCl2 and dimethylamine, (CH3)2NH reacts in the molar ratio 1:2. By considering the number of bond pairs and lone pairs around the central atoms of each molecule, explain the molar ratio and draw a diagram to show the bonding in the product.

4  VJC 2021 8873/02/PRELIM/21 [Turn over …………………………………………………………………………………………….. . …………………………………………………………………………………………….. . …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [2] [Total: 8] 2 (a) Fig. 2.1 shows the trend in melting points of some Period 3 elements: Fig. 2.1 (i) Complete the trend in melting point of the Period 3 elements for aluminium, silicon, chlorine and argon on Fig 2.1. [1] (ii) Explain, with reference to structure and bonding, why magnesium has a higher melting point than sodium. ……………………………………………………………………………………………… . Na Mg Al Si P S Cl Ar melting point / K

5  VJC 2021 8873/02/PRELIM/21 [Turn over ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . [2] (iii ) Explain, with reference to structure and bonding, why sulfur has a higher melting point than phosphorus. ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . ……………………………………………………………………………………………… .

6  VJC 2021 8873/02/PRELIM/21 [Turn over ……………………………………………………………………………………………… . ……………………………………………………………………………………………… . [2] (b) Serpentine has the formula Mg3Si2O5(OH)x. There is currently a lot of interest in the use of serpentine as a “green” cement as it chemically absorbs carbon dioxide, a major constituent of greenhouse gases. (i) Deduce the value of x in Mg3Si2O5(OH)x. [1] (ii) Serpentine reacts with carbon dioxide to form water, silicon(IV) oxide and one other product. Write a balanced equation for this reaction. ……………………………………………………………………………………………… . [1] (c) Dolomite has the formula MgY(CO3)2, where Y is a metal element. Dolomite is insoluble in water but dissolves in aqueous acid due to the reaction between the carbonate ions and hydrogen ions. CO32– + 2H+ → CO2 + H2O A 4.50 g sample of dolomite is dissolved in 25.0 cm3 of 5.00 mol dm–3 hydrochloric acid, in excess. The resulting solution is made up to 100 cm 3 in a volumetric flask using distilled water and labelled solution A. 10.0 cm 3 of solution A is titrated agains t a 0.100 mol dm –3 solution of sodium hydroxide. An average titre of 27.30 cm3 is obtained.

7  VJC 2021 8873/02/PRELIM/21 [Turn over (i) Calculate the amount of hydrochloric acid in 100 cm3 of solution A. [2] (ii) Hence, calculate the amount of hydrochloric acid that reacted with the 4.50 g sample of dolomite. [1] (iii ) Determine the mole ratio of MgY(CO3)2 : CO32 – : H+. [1] (iv ) Hence, calculate the molar mass of Y and suggest its identity. [2] [Total: 13] 3 This question involves the study of the kinetics of decomposition of hydrogen peroxide, H2O2 in the presence of iron(III) nitrate, Fe(NO3)3. H2O2(aq) → H2O(l) + ½O2(g) A small amount of Fe(NO 3)3 was added to 100 cm 3 of 0.200 mol dm –3 H2O2 and the stopwatch was started. At various time intervals, 10 cm3 samples of the reaction mixture was extracted into a conical flask. 50 cm 3 of 0.200 mol dm –3 H2SO4 was added into a sa mple and titrated against 0.0200 mol dm–3 KMnO4.

8  VJC 2021 8873/02/PRELIM/21 [Turn over 2MnO4–(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 8H2O(l) + 5O2(g) Based on the titration results, the concentration of H 2O2 in each 10 cm 3 sample was calculated. A graph of concentration of H2O2 against time was obtained as show in Fig. 3.1. (a) (i) It was observed that the concentration of