O Levels Combined Chemistry G3 O Levels G3 Combined Chemistry Paper 1 mock Name 1 / 20 1. Lead(IV) chloride has a melting point of -15 °C and boiling point of 50 °C. Which type of structure do you expect lead(IV) chloride to have? a simple molecular structure with weak covalent bonds a simple molecular structure with weak intermolecular forces of attraction between molecules a giant molecular structure with strong covalent bonds between atoms a giant ionic crystal lattice structure with strong electrostatic forces of attraction Since the melting point and boiling point are low, it should be a simple molecular structure with weak intermolecular forces of attraction that can be overcome easily. 2 / 20 2. Which diagram best represents the structure of calcium oxide? A B C D Ca is cation and O is anion. They are opposite in charge and attract each other. Thus in the diagram, only black balls are bonded to white balls directly. 3 / 20 3. Which property of elements increases from left to right of Period 3 of the Periodic Table? number of outer shells metallic character tendency to get reduced melting points As you move from left to right across a period, the number of protons in the nucleus increases, which leads to a stronger attraction for electrons. This increased attraction makes it more difficult for an atom to lose electrons, 4 / 20 4. In which chemical reaction does the named product have a higher relative molecular mass than the reactant? the formation of ethanol from glucose the formation of propene from octane the formation of carbon dioxide from butane the formation of dichloromethane from methane methane CH4 molar mass = 12 +4 = 16g dichloromethan CH2Cl2 molar mass = 12 +2 + 71 = 85g 5 / 20 5. Which of the following hydrocarbons would produce the sootiest flame when burnt in air? CH4 C4H10 C8H18 C12H26 The more C atoms in the molecule, the more soot (unburnt hydrocarbon) will be produced 6 / 20 6. Which element does not form a stable ion with the same electronic configuration as neon? Magnesium Fluorine Sodium Sulfur Sulfur is 2,8,6 so when it form an ion, it will be 2,8,8 which is the electron configuration of Argon 7 / 20 7. When a 10 cm3 sample of a gaseous hydrocarbon was completely burnt in 35 cm3 of oxygen, the total volume of the products formed was 50 cm3. Which equation represents the combustion of the hydrocarbon? CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g) C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(g) Since all the reactants and products are gases, we can use the ratio of volume directly without converting to moles. 10: 35 : 50 2 : 7 : 10 ratio of hydrocarbon is 2, ratio of oxygen is 7 and ratio of the sum of products is 10. Only D satisfy this ratio 8 / 20 8. A student investigated the diffusion of ammonia gas, NH3, and hydrogen chloride gas, HCl. Two sets of apparatus were set up as shown below at room temperature and pressure. The damp red litmus paper in apparatus 1 changed colour after 30 seconds. How long does it take for the damp blue litmus paper to change colour in apparatus 2? about 21 seconds about 30 seconds about 64 seconds The blue litmus paper would not change colour. Molar mass of ammonia NH3 = 14+3 =17g molar mass of HCl = 1 +35.5 = 36.5 g HCl will take longer to diffuse as it has a higher molar mass 9 / 20 9. On adding 50 g of impure limestone, CaCO3 (Mr = 100), to excess hydrochloric acid, 6.0 dm3 of CO2 was evolved at room temperature and pressure. What is the percentage purity of the limestone? 25% 50% 75% 100% CaCO3 + 2HCl --> CaCl2 + CO2 + H2O for CO2: 24dm3 --> 1 mole 6 dm3 --> 0.25 mole mole ratio of CO2 : CaCO3 1 : 1 0.25 : 0.25 Molar Mass of CaCO3 = 100g 0.25 mole --> 25g Therefore, % purity = (25/50) x 100% = 50 % 10 / 20 10. CH4, H2O and HCl are covalent compounds. Which atoms in these compounds do not use all their outer shell electrons in bonding? C and H C and O O and Cl Cl and C O has 6 valence electrons and only uses 2 for bonding Cl has 7 valence electrons and only uses 1 for bonding 11 / 20 11. Ammonia and excess carbon dioxide can react to form urea and water in a reaction. 2NH3 + CO2 → CON2H4 + H2O The percentage yield of this reaction is 80 %. What is the mass of ammonia required for this reaction to obtain 60.0 g of urea? [Mr: NH3, 17; CO2, 44; CON2H4, 60; H2O, 18] 10.6 g 27.2 g 34.0 g 42.5 g Molar mass of urea = 60g --> 1 mole 100/80 x 1 = 1.25 mole of urea mole of ammonia = 1.25 x 2 = 2.5 mole mass of ammonia = 2.5 x 17g = 42.5g 12 / 20 12. The diagram shows the apparatus used to separate hexane (boiling point, 70 oC) and heptane (boiling point, 98 oC). A B C D Heptane vapour will condense as it reaches the fractionating column; only hexane vapour will reach the condenser. As the thermometer will only measure the inlet of the condenser, the measured temperature will be constant at the boiling point of hexane until all the hexane has vaporized. 13 / 20 13. Which statement explains why sodium chloride, NaCl, has a lower melting point than magnesium oxide, MgO? Sodium chloride has a simple molecular structure while magnesium oxide has a giant ionic structure. Sodium is more reactive than magnesium. The attraction between Na+ and Cl− is weaker than that between Mg2+ and O2−. The particles in sodium chloride are more closely packed than in magnesium oxide. Both compounds are giant ionic structures. But the magnesium ion charge is 2+ while the sodium ion is 1+. Thus, the electrostatic forces holding the ions together are stronger in magnesium chloride 14 / 20 14. Aqueous hydrogen peroxide decomposes to form water and oxygen gas. Two experiments were carried out to measure the rate of production of oxygen from aqueous hydrogen peroxide. A B C D Experiment B has more starting reactant but lower concentration than A. Therefore, the curve will be less steep but finish higher. 15 / 20 15. A solution of a lithium halide and a halogen are mixed. A reaction occurs and the mixture darkens in colour. What are the reactants? bromine and lithium chloride iodine and lithium fluoride chlorine and lithium iodide chlorine and lithium fluoride Since the solution darken, there must be displacement. 16 / 20 16. Francium, Fr, is an element in the same group of the Periodic Table as lithium, sodium and potassium. Which statement about francium is likely to be correct? It forms a carbonate Fr2CO3. It forms coloured compounds. It reacts slowly with cold water. It is produced from the electrolysis of aqueous francium chloride. Use sodium or potassium as guide. Only extraction with electrolysis is true 17 / 20 17. Which equations below represent redox reactions? 1. H+ + OH− → H2O 2. MnO4− + 8H+ + 5e− → Mn2+ + 4H2O 3. Cl2 + 2Br −→ Br2 + 2Cl − 1 only 3 only 1 and 2 only 2 and 3 only neutralisation ( not redox) redox redox 18 / 20 18. The following chemicals are available in the laboratory. aqueous bromine Universal Indicator solution magnesium powder sodium carbonate Which of these chemicals can be used to distinguish between propene and propanoic acid? All of them 1 only 1 and 4 only 1, 2 and 3 only aqueous bromine --> change colourless/no change Universal Indicator solution --> turns orange/ green magnesium powder --> no change/effervescence sodium carbonate --> no change/effervescence 19 / 20 19. An unknown substance X starts melting at –180 °C and finishes melting at –160 °C. What is substance X likely to be? a compound a mixture an element insufficient data to determine Pure compounds and elements will have a fixed melting point. Only mixtures melt over a range 20 / 20 20. 50.0 cm3 of 0.10 mol/dm3 silver nitrate, AgNO3, is added to 150.0 cm3 of 0.05 mol/dm3 of sodium iodide, NaI, in a beaker. After the reaction, solid silver iodide is present in the beaker. What else is present in the mixture? Ag+, Na+, NO3- only Na+, I-, NO3- only Na+, I- only Na+, NO3- only AgNO3 + NaI --> NaNO3 + AgI 50.0 cm3 of 0.10 mol/dm3 silver nitrate, AgNO3 = 0.005 mole 150.0 cm3 of 0.05 mol/dm3 of sodium iodide, NaI, = 0.0075 mole Reactant ions left = Na+ and I - product ions = Na+ and NO3^- Your score isThe average score is 85% 0% Restart quiz
