NJC Physical Chemistry Revision Part 1

National Junior College 2024 H2 Chemistry Revision Package 1 1) Atoms, Moles and Stoichiometry 1 The hardness present in a water sample due to dissolved calcium ions can be determined by using ion-exchange column as shown in the diagram. Ca2+ + 2H+-resin → Ca2+-resin + 2H+ A 50 cm3 sample of a solution containing calcium sulfate was passed through the ion-exchange resin. The calcium ions in the sample were quantitatively exchanged by hydrogen ions. The sample collected in the flask required 25 cm3 of 1.0 × 10−2 mol dm−3 potassium hydroxide for complete neutralisation. What was the concentration of calcium sulfate in the original sample? A 2.5 × 10−3 mol dm−3 B 5.0 × 10−3 mol dm−3 C 2.0 × 10−2 mol dm−3 D 4.0 × 10−2 mol dm−3 2 5.00 g of a fertilizer containing ammonium sulfate was dissolved in water and diluted to 50 cm3. 25.0 cm3 of this solution was added to an excess of sodium hydroxide solution. The reaction between ammonium sulfate and NaOH(aq) is given by the following equation: (NH4)2SO4 + 2NaOH → Na2SO4 + 2 H2O + 2 NH3 Treated water Ion-exchange resin Hard water

National Junior College 2024 H2 Chemistry Revision Package 2 The ammonia produced was passed into 50.0 cm 3 of 0.050 mol dm −3 sulfuric acid solution. The residual acid then required 25.80 cm 3 of 0.100 mol dm 3 sodium hydroxide solution for complete neutralisation. What is the percentage by mass of ammonium sulfate ( Mr = 132.1) in the fertiliser? A 10.6% B 16.0% C 32.0% D 40.0% 3 A student prepared a 0.100 mol dm−3 solution of Ba(OH)2.8H2O and left it in a beaker. A week later, he returned to the laboratory, used the solution for titration with 0.100 mol dm−3 HCl and was surprised to discover his titres were lower than expected. Which of the following explains why the volume of HC l used was lower than expected? A Some water had evaporated from the barium hydroxide solution B The concentration of HCl was less than the stated 0.100 mol dm−3. C The barium hydroxide crystals had less water of crystallisation than stated. D Some of the barium hydroxide had reacted with carbon dioxide in the air to form solid barium carbonate. 4 Use of the Data Booklet is relevant to this question. How many oxygen atoms are present in 24 cm3 of oxygen gas at r.t.p.? A 24 6.02 1023 32 B

National Junior College 2024 H2 Chemistry Revision Package 3 C D 5 Mixtures of argon and another gas are commonly used during welding. One such gaseous mixture has a density of 1.82 g dm−3 at s.t.p. What could be the other gas in this mixture? [Density of Ar = 1.78 g dm −3 at s.t.p.] A Carbon Dioxide B Oxygen C Nitrogen D Helium 6 X is an organic iron compound containing only Fe, C and H. When a 0.944 g sample of X was subjected to complete combustion, 2.23 g of CO 2 and 0.457 g of H2O were formed. What is the empirical formula of X? A FeCH B FeC2H C Fe2C5H2 D