VJC Prelim P1 Questions Answers

For each question there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1 Use of Data Booklet is relevant to this question. In an experiment, a sample containing 2 different species was vaporised, ionised and passed through an electric field. Analysis of the deflection occurring at the electric region revealed the following data for the sample. It was observed that a beam of 24Mg2+ gives an angle of deflection of +4.0 °. Which one of the following species will give the correct angle of deflection? isotope no. of electrons angle of deflection A 16O 6 –6.0 º B 23Na 10 +2.1 º C 28Si 10 –6.9 º D 35Cl 18 +1.4 º 2 Which one of the following corresponds to the electronic configuration of the 6 outermost electrons of a Group 6 element in its ground state? A 3d4 4s2 B 3d5 4s1 C 4s2 4p4 D 4p6 3 Which of the following have species arranged in increasing bond angle about the central atom? 1 ICl4– IO3–, I3– 2 XeF4, XeO3, XeF2 3 N2O, NO3–, NO2+ 4 SO42–, SO32–, SO2 A 1 and 2 only C 1, 3 and 4 only B 1, 2 and 4 only D 2 and 3 only +4.0 º - + 24Mg2+ Source

4 The molar mass of ethanoic acid is 120.0 g mol–1 when dissolved in trichloromethane but 60.0 g mol–1 when dissolved in water. Which one of the following statements best explains the phenomenon? A Ethanoic acid is more soluble in trichloromethane than in water. B Ethanoic acid molecules form strong covalent bonds with trichloromethane molecules. C Ethanoic acid evaporates more readily in water. D Ethanoic acid molecules form extensive hydrogen bonds with water molecules. 5 1.00 mol of gaseous molecules of a compound A, takes up a volume of 39 dm 3 when subjected to a pressure of 1.52 atm at a temperature of 70 ºC. Which of the following statements explain the above observation? 1 Gaseous molecules of A experiences strong intermolecular forces of attractions. 2 Gaseous molecules of A have a significant molecular volume. 3 Gaseous molecules of A are in constant, rapid, random motion. A 1, 2 and 3 C 2 and 3 only B 1 and 2 only D 1 only 6 P, Q and R are 3 consecutive elements in Period 3 of the Periodic Table.  R has the highest melting point out of the 3 elements.  The chloride of P gives a solution that is least acidic in water as compared to chlorides of Q and R.  The 3rd ionisation energy of Q is much lower than that of P. What can P, Q and R be? A Na, Mg, Al C Al, Si, P B Mg, Al, Si D Si, P, S 7 Which one of the following statement s about Group 2 elements and their compounds is correct? A Calcium hydroxide has a higher solubility than magnesium hydroxide. B Calcium reacts with barium chloride to give calcium chloride. C Strontium carbonate, on heating over a short period of time, decomposes to give more carbon dioxide gas than magnesium carbonate. D Magnesium has a lower melting point than strontium.

8 10 cm 3 of gaseous C xHyOz was burnt in excess oxygen. There was a contraction of 20 cm3. When the gaseous mixture was passed through aqueous sodium hydroxide, there was a further contraction of 30 cm3. All gas volumes were measured at room temperature and pressure. Which one of the following could be CxHyOz? A C3H2O3 C C3H6O2 B C3H4O4 D C3H8O2 9 Aspirin is a medication used to treat pain, fever or inflammation. Aspirin 25.0 cm3 of 1.00 mol dm–3 NaOH was added to 25.0 cm3 of solution containing aspirin. This resulting solution required 35.20 cm3 of 0.325 mol dm–3 HCl to be fully neutralised. What is the concentration of aspirin in the original 25.0 cm3 solution? A 0.229 mol dm–3 C 0.458 mol dm– 3 B 0.271 mol dm–3 D 0.542 mol dm– 3 10 Nitrogen monoxide, NO, is a pollutant that is formed in car exhausts and it can be oxidised as follows: NO(g) + O(g)  NO2(g) What is the enthalpy change of the above reaction given the following information? NO(g) + O3(g)  NO2(g) + O2(g) ∆H = –199 kJ mol–1 O3(g)  O2(g) ∆H = –142 kJ mol–1 O2(g)  2O(g) ∆H = +495 kJ mol–1 A –94 kJ mol–1 C –552 kJ mol–1 B –305 kJ mol–1 D –589 kJ mol–1 COOH OCOCH3 2 3

11 A key step in the production of sulfuric acid is the oxidation of SO2(g) to SO3(g). 2SO2(g) + O2(g)  2SO3(g) At 25 oC, ∆G = –142 kJ mol–1, ∆H = –198 kJ mol–1, ∆S = –188 J K–1 mol–1. Assuming ∆H and ∆S are constant with temperature, which of the following statements about this reaction are correct? 1 The reaction becomes less spontaneous with increasing temperature. 2 The reaction becomes spontaneous at 780 oC. 3 The reaction is spontaneous at 900 oC. A 1, 2 and 3 C 2 and 3 only B 1 and 2 only D 1 only 12 An experiment was carried out to investigate the initial rate of reaction between ammonium peroxodisulphate, (NH4)2S2O8, an oxidising agent, and potassium iodide, KI. The initial concentrations of the (NH 4)2S2O8 and KI solutions in the mixture together wi th the time taken for the mixture to darken for the various experimental runs are given below. initial concentration of (NH4)2S2O8 / mol dm–3 initial concentration of KI / mol dm–3 time taken to darken / s 0.10 0.20 35 0.05 0.20 70 0.10 0.067 105 0.02 0.75 ? What is the expected time taken (in s) to darken when the experiment is repeated using initial concentrations of (NH4)2S2O8 and KI to be 0.02 mol dm–3 and 0.75 mol dm–3 respectively? A 40 B 47 C 60 D 72

13 Ammonia is a raw material used in the manufacture of fertilisers, ex plosives and cleaning fluids. It is produced in the Haber process as shown: N2(g) + 3H2(g) ⇌ 2NH3(g)  A closed system initially containing 2.00 mol of nitrogen, 6.00 mol of hydrogen, and 2.40 mol of ammonia at 448 oC is allowed to reach equilibrium in a sealed vessel of volume 1 dm3. At equilibrium, there was 2.32 mol of nitrogen present.  The vessel is subsequently expanded to 2 dm 3 under constant temperature, and equilibrium re-established. Which of the following statements about this reaction are correct? 1 The equilibrium constant, Kc, is 3.96 x 10–3 mol–2 dm6. 2 The equilibrium will shift to the left when vessel is expanded to double its initial volume. 3 The equilibrium concentration of NH 3(g) is lower after the second equilibrium is established. A 1, 2 and 3 C 2 and 3 only B 1 and 2 only D 1 only 14 Common chlorine bleach is typically a 5 % sodium hypochlorite, NaClO solution. A solution, made by adding solid NaClO to 2 dm3 of water, has a pH of 10.5. How many moles of NaClO was added to the water, given that chloric( I) acid, HClO has a Ka of 3.03 x 10–8 mol dm–3 at 25 oC? A 0.25 mol B 0.31 mol C 0.55 mol D 0.62 mol 15 Hydroxyapatite, Ca5(PO4)3OH, is the main constituent of tooth enamel. In the presence of saliva, which contains a buffer system, the following equilibria exist: Ca5(PO4)3OH(s) ⇌ 5Ca2+(aq) + 3PO43–(aq) + OH–(aq) HPO42–(aq) ⇌ H+(aq) + PO43–(aq) Which one of the following statements does not help to explain why tooth enamel is dissolved more readily when saliva is acidic? A The phosphate ion PO43– accepts H+. B The hydroxide ions are neutralised by the acid. C The calcium ions can precipitate to form Ca(OH)2. D The concentration of PO43– decreases in this medium.

16 A solution contains three anions with the following concentrations: anion concentration / mol dm–3 CrO42– 0.20 CO32– 0.10 Cl– 0.010 A dilute AgNO3 solution is slowly added to the solution. Which is the first compound to precipitate and what concentration of Ag+ is necessary to begin its precipitation? [Given: Ksp (Ag2CrO4) = 1.2 x 10 –12 mol3 dm–9, Ksp (Ag2CO3) = 8.1 x 10 –12 mol3 dm–9, Ksp (AgCl) = 1.8 x 10–10 mol2 dm–6] first ppt [Ag+] to begin precipitation / mol dm-3 A Ag2CrO4 6.00  10–12 B Ag2CrO4 2.45  10–6 C Ag2CO3 9.06  10–6 D AgCl 1.80  10–8 17 Species