H1 Chem P2 SAJC 2024 Ans

1 ST ANDREW’S JUNIOR COLLEGE PRELIMINARY EXAMINATIONS HIGHER 1 CANDIDATE NAME CLASS 2 3 H1 CHEMISTRY 8873 / 02 Paper 2 Structured Questions 27 August 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. Write in dark blue or black pen. You may use a HB 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 use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. Question Number Total Marks Marks Obtained SECTION A 1 14 2 7 3 9 4 30 SECTION B 5 20 6 20 TOTAL 80 This document consists of XX printed pages (including this cover page).

2 Section A Answer all the questions in this section in the spaces provided. 1 This is a question about Group 14 elements and its compounds. (a) (i) A sample of silicon contains three isotopes, as shown in Table 1.1. Table 1.1 Isotope Relative Isotopic mass Percentage abundance. % 28Si 27.976 92.22 29Si 28.976 4.69 30Si 29.973 3.09 Calculate the relative atomic mass of silicon in this sample, giving your answer to two decimal places. [2] Relative atomic mass of silicon = (27.976 x 92.22 + 28.976 x 4.69 + 29.973 x 3.09 ) / 100 = 28.08 (to two decimal places) (ii) Complete the electronic configuration for silicon. [1] 1s2 …………………………… 1s2 2s22p63s23p2 (iii) Explain why second ionisation energy of silicon is lower than that of aluminium. [2] 2nd I.E. of Si is lower than that of Al. Al+: 1s2 2s2 2p6 3s2 Si+ : 1s2 2s2 2p6 3s2 3p1 • In Al+, the electron is removed from the 3s orbital, whereas for Si+, the electron is removed from the 3p orbital.

3 • The electron in the 3p orbital is further from the nucleus √ than the electron in the 3s orbital and experiences additional shielding effect√ by the two 3s electrons. • These factors outweigh the effect of increase in nuclear charge √ from Al+ to Si+, resulting in a weaker attraction by nucleus √ • Hence less energy is required to remove the electron from the 3p orbital in Si+ than that in the 3s orbital in Al+. (b) When carbon tetrachloride, CC l4, and silicon tetrachloride , SiC l4, were added to water, the following observations were seen. carbon tetrachloride Forms two immiscible layers silicon tetrachloride White solid and steamy fumes (i) Write a balanced equation for the reaction of SiCl4 with water. [1] SiCl4(l) + 2H2O(l) → SiO2(s) + 4HCl (aq) (State symbols not required) (ii) CCl4 has no reaction with water. Suggest an explanation for the inertness of CCl4 to water. [1] CCl4 does not have any empty and energetically accessible 3d orbitals that can accept lone pair of electrons from water molecules, hence, it is inert to water. (iii) Explain why CC l4 forms two immiscible layers with water when they are mixed. [2] The energy released to form the instantaneous dipole-induced dipole interactions between CCl4 and water √ is insufficient√ to overcome the hydrogen bonding between water molecules √ and the instantaneous dipole-induced dipole interactions between CCl4 molecules√ . Hence,

4 CCl4 is insoluble in water and forms two immiscible layer when added to water. (c) Due to carbon’s ability to form strong multiple bonds, it can form different allotropes like graphene and fullerene. Graphene is an allotrope of carbon that occurs as two-dimensional sheets while fullerenes are molecules of carbon atoms with hollow shapes. An example of a spherical fullerene is buckminsterfullerene, C60, while carbon nanotube (CNT) is a type of cylindrical fullerene. Buckminsterfullerene has low melting point and is slippery while CNT, like graphene, has high tensile strength and is an excellent conductor of electricity. (i) Graphene is a nanomaterial. Define what is meant by the term nanomaterial. [1] Nanomaterials are defined as a material containing particles where there is at least one dimension between 1-100 nm on the nanoscale. (ii) Draw a diagram to illustrate the structure of graphene. [1] (iii) Explain how carbon nanotube is an excellent conductor of electricity and has high tensile strength. [2] In CNT, there is delocalisation of the electron in the p orbital on each carbon , forming an extended -electron cloud √above and below the layer within the tube allows it to be good electrical conductors.

5 Carbon atoms in graphene form a single layer hexagonal lattice structure, resulting in an extensive network of many strong covalent bonds between carbon atoms give a single carbon nanotube high tensile strength. (iv) Suggest why buckminsterfullerene is a good lubricant. [1] The spherical shape of the buckminsterfullerene allows it to roll/move between the moving parts, reducing contact and friction between parts. [14 marks]

6 2 Propanone, CH3COCH3, reacts with iodine, I2, in the presence of an acid catalyst. An experiment is performed using 1.00 mol dm–3 of I2 and 1.00 mol dm–3 H+(aq) where concentration of CH3COCH3 is monitored over time. The same experiment was then repeated using 0.500 mol dm-3 H+(aq) instead. The results obtained are used to plot the graph below. Fig 2.1 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 [CH3COCH3] /mol dm–3 time / min [H+]= 0.5 mol dm–3 [H+]= 1.0 mol dm–3

7 Fig 2.1 (a) (i) It was found that the reaction is zero order with respect to [I2]. Define the term order of reaction. [1] Order of reaction is the power to which the concentration of the reactant is raised in the rate equation. (b) (i) Use the graph, Fig 2.1, to determine the order of reaction with respect to [CH3COCH3] and [H+] respectively. [2] Since first t1/2 = second t1/2 = 0.035 min, t1/2 is constant at 0.035 min. Order of reaction wrt [CH3COCH3] = 1 Don’t award if no working shown on the graph for the 2 t1/2 interval 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 [CH3COCH3] /mol dm–3 time / min [H+]= 0.5 mol dm–3 [H+]= 1.0 mol dm–3 t1/2 = 0.035 t1/2 = 0.035 (0.044, 0.01) (0.065, 0.02) (0.0, 0.05)

8 When [H+] = 1.0 moldm-3, initial rate = | 0.01−0.05 0.044−0 | = 0.909 When [H+] = 0.5 moldm-3, initial rate = | 0.02−0.05 0.065−0 | = 0.462 When [H+] x 2, rate x 2, Order of reaction wrt [H+] = 1 (ii) Write the rate equation for this reaction. Hence, calculate the value of rate constant, k. Include the units. [2] Rate = k [H+][CH3COCH3] k = 0.0909 0.05 = 18.2 mol–1dm3min–1 (c) Other halogens, like chlorine and bromine, can also react with propanone in similar reactions as iodine. Describe and explain how the reactivity of halogens varies down the group. Include relevant data from the Data Booklet in your answer. [2] Atomic radius of Cl = 0.099nm Atomic radius of Br = 0.114nm Atomic radius of I = 0.133 nm Down the group, the oxidising power of halogens decreases √ because its atomic radius increases and its electron affinity decreases √. Hence, there is less tendency for halogens to gain electrons √ to be reduced to form halide ions. OR Down the group, the oxidising power of halogens decreases √ because valence electrons of halogens are further away from nucleus , and hence, are less attracted to the nucleus √. As a result, it is harder for halogens to gain electrons √ to be reduced to form halide ions.

9 [7 marks] 3 A samp