O Levels Combined Chemistry G3 O Levels G3 Combined Chemistry Paper 1 mock Name 1 / 20 1. 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 % 2 / 20 2. Heavy water is made up of 2 deuterium( Hydrogen atoms with mass number 2) atoms and 1 oxygen atom. Which properties are true about heavy water? 1 Its boiling point is higher than 100 °C. 2. It reacts with sodium to form sodium hydroxide and hydrogen gas. 3 It can act as a solvent for sodium chloride. 1 only 2 and 3 only 1, 2 and 3 none of the above Heavy water has a higher molar mass as compared to normal water, and the boiling point will be slightly higher. Howeve,r most of the chemical properties will be similar. 3 / 20 3. 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 4 / 20 4. 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% 5 / 20 5. 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 6 / 20 6. 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, 7 / 20 7. 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 8 / 20 8. 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. 9 / 20 9. Elements X and Y combine to form an ionic compound. Atoms of X have more protons than atoms of Y. Atoms of Y have more valence electrons than atoms of X. Which statement is correct? Ions of X are negatively charged. Atoms of X have more electron shells than atoms of Y. X and Y are in the same period of the Periodic Table. X and Y are in the same group of the Periodic Table. X and Y, one is metal, one is non-metal. since Y has more valence then X is metal and Y is non-metal and X has more electron shell since it has protons. 10 / 20 10. When crude oil is fractionally distilled, which list best describes the mixture of compounds collected at the bottom of the fractionating column? Short chain molecules, low viscosity, high flammability Short chain molecules, low boiling point, low flammability Long chain molecules, high flammability, high boiling point Long chain molecules, high viscosity, high boiling point The molecules with the greatest molar mass and longest chain are collected at the bottom. They have the highest boiling point and are hard to ignite 11 / 20 11. The flowchart shows some reactions of a compound T. What could compound T be? aluminium carbonate ammonium nitrate calcium nitrate zinc carbonate Ammonium salt + Strong Alkali --> ammonia gas + water + salt test for nitrate: add sodium hydroxide solution to the sample, followed by aluminum foil, and gently heat the mixture. If nitrate ions are present, they will be reduced to ammonia gas, which can be detected by its pungent smell or by its ability to turn damp red litmus paper blue. 12 / 20 12. Which of the following statements about a homologous series is correct? The melting and boiling point increases with increasing relative molecular mass. The members have similar physical properties. The members have the same molecular formula. The relative molecular masses of consecutive members differ by 12. The physical properties of members show a trend 13 / 20 13. 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 14 / 20 14. 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 15 / 20 15. Which substances contain the same number of atoms? A B C D 16 / 20 16. An unknown solid Q has the following properties. •When aqueous sodium hydroxide is added until in excess to the solution, no visible reaction is observed. • When dilute acid is added to Q, effervescence of a colourless gas is observed. • Q dissolves in water to form a colourless solution. • Q is stable to heat. What is Q likely to be? ammonium carbonate copper(II) hydroxide sodium carbonate zinc carbonate • When aqueous sodium hydroxide is added in excess to sodium carbonate, no reaction takes place • When dilute acid is added to sodium carbonate, carbon dioxide is evolved. • Sodium carbonate is soluble in water and form a colourless solution. • sodium carbonate is stable to heat. 17 / 20 17. 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 18 / 20 18. 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 19 / 20 19. 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 20 / 20 20. 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 Your score isThe average score is 85% 0% Restart quiz
