2024 PU2 H1 Chem Paper 2 (QP) MI

Class Adm No Candidate Name: This question paper consists of 19 printed pages and 1 blank page. 2024 Preliminary Exams Pre-University 2 H1 CHEMISTRY 8873/02 Paper 2 Structured Questions 9 Sep 2024 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number on all the work you hand in. Write in dark blue or black pen. You may use an 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. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Question Section A Section B Total 1 2 3 4 5 6 7 Marks 11 18 16 6 9 20 20 80 H

2 Section A Answer all the questions in this section in the spaces provided. 1 Silicon compounds are used in the production of glass, ceramics, and refractory materials. Silicon dioxide is a major component of glass and is used in a wide range of applications, including construction, optics, and consumer products. (a) A sample of silicon contains three isotopes, as shown in Table 1.1. Table 1.1 Isotope Percentage abundance / % 28Si 92.23 29Si 4.67 30Si 3.1 (i) Define the term relative atomic mass of silicon. ………………………………………………………………………………………………… [1] (ii) Calculate the relative atomic mass of silicon from this sample, giving your answer in two decimal places. [1] (b) (i) State the full electronic configuration of silicon. Si : .…………………………………………………………………………………………… [1] (ii) With reference to the Data Booklet, compare the values of second and third ionisation energies of silicon. Explain why these two energies are different and include an equation representing the third ionisation energy of silicon in your answer. …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [3]

3 [Turn over (c) Describe the reaction, if any, of silicon dioxide with water. Include the approximate pH value of any resulting solution. ……………………………………………………………………………………………………… [1] (d) Silicon dioxide can react with carbon under high temperature to form silicon carbide, SiC. Silicon carbide has a high melting point of 2730 °C. It is very hard and can be used as a semiconductor material. (i) Suggest the type of structure and bonding of SiC. Structure : ………………………………………………………………………………………. Bonding : …………………………………………………………………………………… [1] (ii) Another method to produce silicon carbide uses silane, SiH4, and methane gas. SiH4 + CH4 → SiC + 4H2 Draw the ‘dot-and-cross’ diagram of silane. State and explain the shape and bond angle around the silicon atom in silane. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [3] [Total: 11]

4 2 (a) Silver can exist in the form of nanoparticles. The properties of silver nanoparticles make them valuable in a wide range of fields, from healthcare to materials science. (i) Define the term nanoparticle. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] (ii) Suggest why silver nanoparticles are more effective catalysts compared to a single 1 cm3 block of silver metal. …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2] (iii) Suggest how silver nanoparticles may have an effect on human health. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] (iv) Silver can be synthesised in the form of nanoparticles, while graphene can be synthesised as a nanomaterial. Describe the structure of graphene and use it to explain why graphene has a high tensile strength. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2]

5 [Turn over (b) Silver bromide is a sparingly soluble salt that can dissolve in concentrated ammonia. When ammonia is added to silver bromide, a diamminesilver(I) complex ion, [Ag(NH3)2]+, is formed. AgBr(s) + 2NH3(aq) ⇌ [Ag(NH3)2]+(aq) + Br−(aq) Kc = 8.5 × 10-6 (i) Write the expression for the equilibrium constant for the above reaction, including its units. [2] (ii) In an experiment, solid silver bromide was added to aqueous ammonia. Given that the equilibrium concentration of NH 3 is 0.50 mol dm -3, calculate the equilibrium concentration of [Ag(NH3)2]+. [2] (iii) Explain the effect of adding excess concentrated ammonia on I the position of equilibrium II Kc I ………………………………………………………………………………………………….. ………………………………………………………………………………………………….... II ………………………………………………………………………………………………… ………………………………………………………………………………………………… [3] (iv) Predict the sign for the enthalpy change when one mole of AgBr is dissolved in water. Explain your answer. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2]

6 (c) Table 2.1 contains the values of lattice energies of AgBr and MgO. Table 2.1 Compound Theoretical value / kJ mol-1 Experimental value / kJ mol-1 AgBr 905 795 MgO 3795 3791 (i) Explain why the lattice energy of MgO is considerably larger in magnitude than AgBr. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2] (ii) There is close agreement between the experimental and theoretical values of lattice energy for MgO but not for AgBr. Suggest a reason for this. …………………………………………………………………………………………………… ………………………………………………………………………………………………… [1] [Total: 18]

7 [Turn over 3 Polymers are used in a wide range of applications across industries due to their diverse properties. The properties related to the different polymers are shown in Table 3.1. Table 3.1 polymer structure of repeat unit of polymer chemical reactivity strength rigidity high density poly(ethene) (HDPE) Low High Moderate Kevlar ® Structure W Very low Very High High poly(chloroethene) (PVC) Moderate High High poly(ethene) terephthalate (PET) Moderate High Moderate (a) State the type of reaction when PVC reacts with aqueous NaOH and write an equation for the reaction. Type of reaction: …………………………………………………………………………………… Equation: [2]

8 (b) The following structures are the monomer units of Kevlar ®. terephthalic acid p-phenylenediamine (i) Explain, in terms of structure and bonding, the differences in melting point between the two monomer units of Kevlar ®. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ..............................................................