RI Y4 2022 FE Revision Formulae Mole concept ANS.pdf

1 Raffles Institution Raffles Programme Year Four Chemistry Name: ____________________________ ( ) Class: ______ Date: _______ 2022 FE Revision – Formulae, Stoichiometry and Mole Concept Answers 1 a. magnesium nitrate Mg(NO3)2 g. ammonium sulfate (NH4)2SO4 b. copper(II) carbonate CuCO3 h. ammonia NH3 c. iron(III) sulfate Fe2(SO4)3 i. sulfur dioxide SO2 d. sodium oxide Na2O j. propene C3H6 e. calcium hydroxide Ca(OH)2 k. ethanol C2H5OH f. potassium manganate(VII) KMnO4 l. ethanoic acid CH3COOH 2 The relative molecular mass, Mr, of a molecular substance is the average mass of one molecule compared with one-twelfth of the mass of an atom of carbon-12. 1 mol of a substance contains 6 x 1023 particles. 1 mol of any gas occupies 24 dm3 at room temperature and pressure. 1.0 mol of ammonia, NH3 (molecular compound) contains • 6 x 1023 x 1.0 = 6 x 1023 NH3 molecules • 6 x 1023 N atoms • 6 x 1023 x 3 = 1.8 x 1024 H atoms 0.5 mol of ammonium sulfate, (NH4)2SO4 (ionic compound) contains • 6 x 1023 x 0.5 = 3 x 1023 (NH4)2SO4 formula units • 3 x 1023 x 2 = 6 x 1023 NH4+ ions • 3 x 1023 SO42− ions Practice Questions 1 D 2 C 3 A 4 A 5 A 6 D 7 (a)(i) to absorb water vapour (ii) nitrogen (b) 3.50 g (c) 11.00 g (d) 85.7% (e) CH 2 (f) C3H6 8 (a) 0.400 mol dm−3 (3sf) (b)(i) 0.100 mol dm−3 (3sf) (ii) 20.5 cm3 (3sf) (iii) 19.5 cm3 (3sf) 9 (a) 2HCl (aq) + CaCO 3 (s)  CaCl2 (aq) + CO2 (g) + H2O (l) (b) 0.00365 mol (c) 0.300 mol dm−3 (3sf) 10 (a) CO 2 (g) + 2NaOH (aq)  Na2CO3 (aq) + H2O (l) (b) 0.0284 mol (3sf) (c) 0.0108 mol (3sf) (d) 95.0% (e)(i) N2 + 3H2  2NH3 (ii) amount of NH3 = 0.0180 14+1+1+1 = 0.001059 mol amount of N2 = 0.001059 x 0.5 = 0.000529 mol % by mass of N2 = 0.000529 x (14x2) 0.500 x 100% = 2.96% (3sf)