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 FeC10H10 7 0.0337 g of an organic compound when vapourised completely at 100 kPa and 300 K occupied a volume of 20 cm 3. When this volume of vapour was completely burnt in excess oxygen, 40 cm 3 of carbon dioxide and 20 cm 3 of water vapour were formed. All volumes were measured at the same temperature and pressure. What is the formula of the organic compound? A C2H2 B C3H6 C CH2CO D CH3CHO 8 A sample of 10 dm3 of polluted air at r.t.p is passed through limewater so that all carbon dioxide present is precipitated as calcium carbonate. The mass of calcium carbonate formed is 0.05 g. What is the percentage, by volume, of carbon dioxide in the air sample? [A r C, 12.0; O, 16.0; Ca, 40.1] A 0.03% B 0.05% C 0.12% D 0.60%

National Junior College 2024 H2 Chemistry Revision Package 4 9 A student added 10 cm 3 of 0.2 mol dm −3 KI(aq) to 10 cm 3 of 0.2 mol dm −3 CuSO4(aq) in a beaker and observed that a white precipitate in brown solution was obtained. She knew that if she were to add S2O32−(aq) to the mixture, the brown solution will be decolourised. Calculate the volume of 0.04 mol dm −3 S2O32−(aq) she should add to the mixture in the beaker in order to completely decolourise the brown solution. A 12.5 cm3 B 15.0 cm3 C 16.7 cm3 D 25.0 cm3 10 Which of the following contains the greatest number of moles of particles? A 600 g of I2(s) B 50 cm3 of H2O(l) C 50 dm3 of HCl(g) at s.t.p. D 550 cm3 of 2.5 mol dm–3 CH3CO2H(aq) 11 1 Naturally-occurring silicon is a mixture of three isotopes, 28Si, 29Si and 30Si. The relative atomic mass of silicon is 28.109 What could be the relative abundance of each of the three isotopes? A 91.1% 28Si, 7.9% 29Si and 1.0% 30Si B 92.2% 28Si, 4.7% 29Si and 3.1% 30Si C 95.0% 28Si, 3.2% 29Si and 1.8% 30Si D 96.3% 28Si, 0.3% 29Si and 3.4% 30Si 12 2 Which statements about 28.0 g sample of 14N2 are correct? 1 The number of atoms is the same as the number of atoms in 24.0 g of 12C. 2 The number of atoms is the same as the number of atoms in 4.0 g of 4He.

National Junior College 2024 H2 Chemistry Revision Package 5 3 The number of molecules is the same as the number of atoms in 32.0 g of 16O2. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 13 Which statement about one mole of a metal is always correct? A It contains the same number of atoms as mol of hydrogen gas B It contains the same number of atoms as mol of 12C. C It has the same mass as 1 mol of hydrogen atoms. D It is liberated by 1 mol of electrons. 14 Naturally occurring iron consists of four isotopes, 54Fe, 56Fe, 57Fe and 58Fe. Two ions formed by the isotopes have chemical formulae shown below: Which of the following statements is true? A The electron configuration of both Fe2+ ions is1s22s22p63s23p63d44s2. B When subjected to an electric field, ion gives a greater angle of deflection than ion C ion has more protons in its nucleus than ion. D The total number of protons and electrons in each of the Fe2+ ions is smaller than the nucleon number of the respective ion.

National Junior College 2024 H2 Chemistry Revision Package 6 15 (SAJC 14) A solid hydrocarbon was completely combusted in a closed vessel at 120 oC. The residual gas had a volume of 64 cm3, which decreased by 24 cm3 after bubbling through a dehydrating agent. After this, 40% of the final gas volume consisted of oxygen. What is the empirical formula of the hydrocarbon? A CH B CH2 C CH3 D C2H3 16 (NYJC 14) 0.02 mol of CxHyNO2 was burned in excess of oxygen as shown by the equation below. CxHyNO2 + aO2 → xCO2 + NO2 + H2O The gases that were produced were first passed through a U-tube containing phosphorus pentoxide and then bubbled through 0.25 mol of NaOH(aq). The equations illustrating the reactions of the gases with NaOH(aq) are as shown below. CO2 + 2NaOH → Na2CO3 + H2O 2NO2 + 2NaOH → NaNO2 + NaNO3 + H2O The phosphorus pentoxide U-tube increased in mass by 1.15 g and the excess NaOH required 40.00 cm3 of 0.875 mol dm−3 H2SO4 for complete reaction. What is the ratio of x:y? A 2:3 B 4:3 C 4:7 D 8:7

National Junior College 2024 H2 Chemistry Revision Package 7 17 (VJC 13) 25.0 cm3 of a solution of hydrogen peroxide, H2O2, was oxidised by excess potassium manganate(VII) solution under acidic condition. The volume of oxygen gas produced at room temperature and pressure was 26 cm3. What is the concentration of hydrogen peroxide in the solution? A 2.89 x 10–2 mol dm–3 B 4.33 x 10–2 mol dm–3 C 8.66 x 10–2 mol dm–3 D 1.30 x 10–1 mol dm–3 Section B 1(a) [CJC/07] 0.50 g of hydrated iron(II) sulfate (FeSO4.7H2O) was dissolved in dilute H2SO4 and titrated with 0.02