O Levels Combined Chemistry G3 O Levels G3 Combined Chemistry Paper 1 mock Name 1 / 20 1. Three elements W, X, Y, and Z have consecutive, increasing proton (atomic) numbers. Element Y exists as a colourless, monatomic gas at room temperature. Which will be the chemical formula of a compound formed between W and chlorine? WCl W2Cl WCl2 W2Cl3 Y would be noble gas and thus W is in group 16 with 6 valence electrons and need 2 more Cl has 7 valence and need 1 more so the formula will be WCl2 2 / 20 2. Which statement does not explain why the speed of the reaction between zinc and dilute sulfuric acid increases when the acid is warmed? The particles are moving faster as they gain more energy. The activation energy of the reaction decreases. The particles are colliding more frequently. More particles have sufficient energy required for the reaction. An alternative pathway with lower activation energy is only provided by a catalyst, not a higher temperature 3 / 20 3. Which substances contain the same number of atoms? A B C D 4 / 20 4. 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. 5 / 20 5. 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. 6 / 20 6. Which one of the following could be used to distinguish aqueous solutions of sodium chloride and sodium iodide? aqueous barium chloride aqueous silver nitrate aqueous sodium hydroxide aqueous sulfuric acid When silver nitrate is added, PPT of silver chloride(white) and silver iodide(yellow) will be formed, respectively 7 / 20 7. Calcium nitrate crystals contain water of crystallisation. Its formula may be written as Ca(NO3)2●nH2O. When a 7.00 g sample of hydrated calcium nitrate is heated to remove all water, 4.90 g of anhydrous calcium nitrate remains after heating. What is the value of n? 1 2 3 4 7 g - 4.9 g = 2.1g of water 1 mole water --> 18g 2.1 g --> 0.11667 mole 1 mole Calcium nitrate --> 164g 4.9g --> 0.029878 mole ratio 0.029878 : 0.11667 1 : 4 8 / 20 8. An impure sample of calcium carbonate with a mass of 1.70 g was reacted with excess hydrochloric acid and 360 cm3 of carbon dioxide was collected at room temperature and pressure. What is the percentage purity of the calcium carbonate? 75% 88% 90% 98% CaCO3 + 2HCl --> CaCl2 + CO2 + H2O 1 mole --> 24000 cm3 360 cm3 --> 0.015 mole Ratio of CaCO3 : CO2 1:1 mole of CaCO3 = 0.015 mole molar mass of CaCO3 = 100g mass = 0.015 x 100 = 1.5g % purity = 1.5/1.7 x 100% = 88.2% 9 / 20 9. A reaction takes place in two stages in the presence of a catalyst: Which ion is the catalyst in the reaction? Fe^2+ (aq) I^– (aq) SO4^2– (aq) S2O8^2– (aq) The catalyst must remain unchanged at the end of the reaction. 10 / 20 10. Which compound has the lowest percentage by mass of nitrogen? (NH2)2CO (NH4)2SO4 (NH4)3PO4 NH4NO3 % of N in (NH2)2CO = 46.65 % % of N in (NH4)2SO4 = 21.2% % of N in (NH4)3PO4 = 28.18% % of N in NH4NO3 = 35% 11 / 20 11. When excess aluminium oxide, Al2O3 was added to a portion of dilute sodium hydroxide. Which of the following correctly describes the pH change and the explanation? A B C D Aluminium oxide is amphoteric and neutralises the sodium hydroxide. Thus the pH decrease 12 / 20 12. 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 13 / 20 13. 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 14 / 20 14. A warship had its hull plated in copper to protect its wooden hull from rotting. However, after 2 years at sea, it was found that the iron parts of the warship in contact with the copper plates were more corroded than normal. What is the best explanation for this observation? Copper acts as a catalyst to speed up corrosion. Copper reacts with the iron to increase corrosion. Iron displaces copper to form iron(III) oxide. Iron is more reactive and corrodes in place of copper. Iron is above copper in the reactivity series. Iron will readily give away electrons to copper. Thus, iron will ionize easily to react with the oxygen in the air to rust. 15 / 20 15. A paper chromatography experiment was carried out to determine the inks present in a mixture, and the results shown below were obtained. Which statement about the results is incorrect? Ink 4 is more soluble than ink 3 in the solvent used. Inks 1 and 2 contained more than one colour pigment. The ink mixture contained inks 1, 3 and 4. The Rf value of ink 3 in the solvent used is more than 0.5. The further the ink moved from the starting line, the more soluble it is in this solvent 16 / 20 16. 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 17 / 20 17. How many of the following processes will lead to an increase in greenhouse gas emissions? 1 2 3 4 decomposition -> give out carbon dioxide fermentation -> give our carbon dioxide photosynthesis -> take in carbon dioxide polymerisation -> none, maybe water respiration -> give out carbon dioxide neutralisation -> only salt and water 18 / 20 18. The structure of brass is shown below. What is the purpose of adding zinc to copper? to make the packing of atoms more compact to strengthen the metallic bonds between copper atoms to prevent layers of copper atoms from sliding over each other easily to prevent the ‘sea of electrons’ from moving freely in the metal lattice Adding zinc atoms to copper disrupts the orderly arrangement, which prevents layers of copper atoms from sliding over each other easily. The effect is that the alloy is now harder and stronger than pure copper. 19 / 20 19. 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. 20 / 20 20. 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 Your score isThe average score is 85% 0% Restart quiz
