page 09 22. A compound was found to have the percentage composition by mass as shown below. vanadium 61.4% oxygen 38.6% This compound has the formula A VO B VO2 C V2O D V2O3 23. Which of the following compounds could be used as a primary standard? A Calcium carbonate B Hydrochloric acid C Sodium carbonate D Sodium hydroxide 24. The total mass of the Earth’s atmosphere has been determined to be 5.1 × 1018 kg. What mass, in kg, of carbon dioxide is in the Earth’s atmosphere if the concentration of carbon dioxide is 420 ppm? A 1.2 × 1013 B 2.1 × 1015 C 1.2 × 1016 D 2.1 × 1018 25. The concentration of Pb2+ ions in a solution can be determined using the following sequence of reactions: Pb2+(aq)  +  CrO4 2−(aq)  ↓  PbCrO4(s) PbCrO4(s)  +  2Cl−(aq)  ↓  PbCl2(s)  +  CrO4 2−(aq) 2CrO4 2−(aq)  +  6I−(aq)  +  16H+(aq)  ↓  2Cr3+(aq)  +  3I2(aq)  +  8H2O(ℓ) How many moles of iodine are formed from one mole of Pb2+ ions in the solution? A 0.75 B 1.5 C 3.0 D 6.0 [END OF SECTION 1. NOW ATTEMPT THE QUESTIONS IN SECTION 2 OF YOUR QUESTION AND ANSWER BOOKLET.] page 10 [BLANK PAGE] DO NOT WRITE ON THIS PAGE page 11 [BLANK PAGE] DO NOT WRITE ON THIS PAGE page 12 [BLANK PAGE] DO NOT WRITE ON THIS PAGE