CGSS 2023 Chemistry Prelim Paper 1 Answers

2023 Chemistry Prelims Paper 1 Answers 1 A 11 C 21 B 31 C 2 B 12 D 22 A 32 C 3 D 13 D 23 C 33 B 4 C 14 A 24 A 34 C 5 C 15 D 25 A 35 A 6 A 16 D 26 D 36 B 7 A 17 B 27 B 37 B 8 C 18 A 28 B 38 C 9 C 19 B 29 A 39 D 10 C 20 A 30 D 40 B

1 Answer: A X consists of two substances R and Y. Therefore it is a mixture. Since Y cools at a fixed temperature, it is a pure substance. 2 Answer: B Bromine and molecules in the air are in constant random motion. 3 Answer: D When silver nitrate is added to barium iodide, a yellow precipitate of silver iodide is formed. The filtrate is aqueous barium nitrate. When dilute sulfuric acid is added to the filtrate, a white precipitate of barium sulfate is formed. The filtrate conta ins nitric acid, which is made up of hydrogen ions and nitrate ions. 4 Answer: C Helium, having a proton number of 2, has an electronic configuration of 2, and has 2 electrons in the outer shell. Lithium, having a proton number of 3, has an electronic c onfiguration of 2,1, has 1 electron in the outer shell. Neon, having a proton number of 10, has an electronic configuration of 2,8, has 8 electrons in the outer shell. 5 Answer: C since X forms cation of X2+, the ionic compound formed with fluorine is XF2. 6 Answer: A Ammonium chloride consists of ammonium ion and chloride ion – an ionic bond exists between them. Ammonium ion has covalent bonds between nitrogen and hydrogen atom 7 Answer: A The intermolecular forces of attraction between covalent molecules are overcome when the covalent liquid boils. 8 Answer: C No. of moles of chlorine gas = 71 71 = 1 mol Since volume ratio = mole ratio for gases, No. of moles of phosphorus vapour = 1 mol Molar mass of phosphorus molecule = mass no. of moles = 124 1 = 124 g/mol No. of moles of phosphorus atoms in a molecule of phosphorus = mass atomic mass = 124 31 = 4 mol Therefore, the formula is P4.

9 Answer: C Molar mass of metal chloride = 74.5 Mass of metal = 74.5 – 35.5 = 39 Therefore, the metal is in group I and the formula of the chloride formed is YCl. 10 Answer: C H+(aq) + OH−(aq) → H2O(l) Since 0.1 mol of H+ and 0.1 mol of OH− are used, both reactants are limiting. 0.1 mol of water would be formed. The energy given out would be 0.1 x 54 = 5.40 kJ 11 Answer: C Relative atomic mass = 1 5 × 10 + 4 5 × 11 = 10.8 12 Answer: D Ammonium salt reacts with alkali to produce ammonia, which turns damp red litmus paper blue. Based on the given information, ammonium nitrate, NH4NO3, is present in the fertiliser. The empirical formula is N2H4O3. 13 Answer: D The spoon should be the negative electrode so that copper(II) ions can be reduced to plate the spoon with copper. This is a electrolytic cell. 14 Answer: A Chemical equation for the electrolysis of concentrated sodium chloride 2H+(aq) + 2Cl− (aq) → H2(g) + Cl2(g) No. of moles of sodium chloride = 58500 23+35.5 = 1000 mol