2025 YIJC H1 Chem Prelim P1 Solutions (for exchange)

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME SUGGESTED ANSWERS CG H1 GROUP 1 / 2 / 3 CHEMISTRY Paper 1 Additional Materials: Multiple Choice Answer Sheet Data Booklet 8873 /01 XX September 2025 1 hour READ THESE INSTRUCTIONS FIRST This document consists of 19 printed pages. Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name and class in the spaces at the top of this page and on the Answer Sheet in the spaces provided unless this has been done for you. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate.

©YIJC [Turn over 2 1 The table below contains incomplete information about three ions, E, F and G, which are isoelectronic (same number of electrons). The atoms of F and G are isotopes. ion mass number atomic number number of neutrons number of electrons charge E 55 25 y F 56 26 G x 31 3+ What are the possible values of x and y? x y A 56 2+ B 56 3+ C 57 2+ D 57 3+ Answer: C ion Mass number Atomic number Number of neutrons Number of electrons charge X 55 25 30 23 2+ Y 56 26 30 23 3+ Z 57 26 31 23 3+

©YIJC [Turn over 3 2 In two separate experiments, a beam of protons and a beam of electrons, travelling at the same velocity, is passed through an electric field as shown. Which set of observations is correct? A The two beams are deflected in opposite directions. The electron beam is deflected the most. B The two beams are deflected in opposite directions. The proton beam is deflected the most. C The two beams are deflected in the same direction. The electron beam is deflected the most. D The two beams are deflected in the same direction. The proton beam is deflected the most. Answer: A Protons are positively charged and hence are deflected towards the negative plate. Electrons are negatively charged and hence are deflected towards the positive plate. As electrons are lighter than protons, electrons are deflected more than protons. 3 Use of the Data Booklet is relevant to this question. Which species has three unpaired electrons? A Al B Ti3+ C Zn2+ D Cr3+ Answer: D Al : 1s2 2s2 2p6 3s2 3p1 Ti3+ : 1s2 2s2 2p6 3s2 3p6 3d1 Zn2+ : 1s2 2s2 2p6 3s2 3p6 3d10 Cr3+ : 1s2 2s2 2p6 3s2 3p6 3d3 Beam of particles + – Source

©YIJC [Turn over 4 4 Use of the Data Booklet is relevant to this question. How many atoms are there in 100 cm3 of oxygen gas measured at s.t.p.? A 2.51  1021 B 2.65  1021 C 5.02  1021 D 5.30  1021 Answer: D Amount of O2 = (100 ÷ 1000) ÷ 22.7 = 0.0044053 mol No. of O2 molecules = 0.0044053 x 6.02 x 1023 = 2.652 x 1021 No. of O atoms = 2.652 x 1021 x 2 = 5.30 x 1021 5 The relative atomic mass of antimony, which consists of the isotopes 121Sb and 123Sb, is 121.8. Calculate the percentage of 123Sb in the isotopic mixture. A 40% B 45% C 50% D 60% Ans: A Let the percentage of 123Sb in the isotopic mixture be x% 𝑥 100 (123) + 100 − 𝑥 100 (121) = 121.8 123x -121x = 80 x = 40 6 The boiling point of ethylamine, CH3CH2NH2, is 16.6 °C. Which bonds are broken when ethylamine is boiled? 1 instantaneous dipole-induced dipole interactions 2 hydrogen bonds 3 covalent bonds A 1, 2 and 3 B 1 and 2 C 2 and 3 D 1 only Answer: B Boiling point of molecules results in overcoming intermolecular forces of attractions. The main dominant intermolecular force present in ethylamine is hydrogen bonds. The weaker id-id attractions are also present.

©YIJC [Turn over 5 7 Three substances, H, J and K, have physical properties as shown. substance H J K melting point / oC 801 –7 3550 boiling point / oC 1413 59 4827 electrical conductivity when in solid state poor poor good What could be the identities of H, J and K? H J K A bromine sodium chloride graphite B bromine sodium chloride silicon dioxide C sodium chloride bromine graphite D sodium chloride bromine silicon dioxide Answer: C Ionic compound NaCl is a non-electrical conductor in solids as ions are fixed in position. Bromine is a covalent compound with no mobile ions and no mobile electrons. Graphite is an electrical conductor due to free delocalised electrons along the layers. Melting and boiling points of bromine is lower than NaCl as the instantaneous dipole -induced dipole interactions between bromine molecules is weaker than the electrostatic forces of attraction between oppositely charged ions in NaCl.

©YIJC [Turn over 6 8 The kinetics of a zero order reaction L → M was investigated. A pair of quantities was plotted and the following graph was obtained. Which pair of quantities gives the graph above? y-axis x-axis A rate [L] B rate [M] C [L] time D [M] time Answer: C For a zero order reaction, rate is independent of concentration of reactant. So, the rate vs [reactant] graph is as such: While the [reactant] vs time graph is as such: 0 y-axis x-axis rate [A] 0 [A] time 0

©YIJC [Turn over 7 9 There are 39 known isotopes of radon (Rn) from 193Rn to 241Rn. The most stable isotope is 222Rn with a half-life of 3.8 days. Given that the decay of 222Rn is a first order reaction , how long will it take for 222Rn to decrease to one-eighth of its original amount? A 7.6 days B 11.4 days C 15.2 days D 30.4 days Answer: B 𝐶(𝑓𝑖𝑛𝑎𝑙) 𝐶(𝑖𝑛𝑖𝑡𝑖𝑎𝑙) = ( 1 2) 𝑛 1 8 = (1 2) 𝑛 n = 3 time taken = 3 X 3.8 = 11.4 days 10 Which changes in conditions would result in a change in the value of the equilibrium constant, Kc, for the following reaction? N2(g) + 3H2(g) ⇌ 2NH3(g) ∆H = −92 kJ mol−1 1 increasing temperature 2 increasing the concentration of N2 3 adding a catalyst A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only Answer: D Kc is only affected by temperature. It is not affected by the concentration of reactants or products or by the presence of catalyst. 11 Ethanol in blood can be assumed to be in dynamic equilibrium with ethanol in breath. This equilibrium forms the basis of the roadside breathalyser test. C2H5OH (blood) ⇌ C2H5OH (breath) The equilibrium constant, Kc, for this equilibrium is 4.3 x 10−4. The concentration of ethanol in a motorist's blood is found to be 75 mg in 100 cm3 of blood. What is the concentration of ethanol in the motorist's breath in mg per 100 cm3? A 3.23 x 10−4 B 3.23 x 10−2 C 1.74 x 105 D 3.23 x 106 Answer: B

©YIJC [Turn over 8 Kc= [C2H5OH(breath)] [C2H5OH(blood)] Kc=4.3 x 10-4= [C2H5OH(breath)] 75 [C2H5OH(breath)] = 0.3225 = 3.23 x 10−2 mg per 100 cm3 12 Hydrogen reacts with iodine to form hydrogen iodide . This reaction is reversible and is allowed to reach an equilibrium. H2(g) + I2(g) ⇌ 2HI(g) ∆H = +26.5 kJ mol−1 At time = t1, the temperature was increased. Which graph correctly sho