1. The percent by mass of nitrogen in Mg(CN) 2 is equal to 1) 3)

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1 1. The percent by mass of nitrogen in Mg(CN) 2 is equal to 2. A compound consists of 40.% sulfur and 60.% oxygen by mass. What is the empirical formula of this compound? 1) SO 2) SO 2 3) SO 3 4) SO 4 3. What is the empirical formula of a compound if a sample contains 8.52 grams of carbon and 1.42 grams of hydrogen? 1) C 2 H 2) CH 2 3) CH 4) C 2 H 2 4. If the density of a gas at STP is 2.50 grams per liter, what is the gram molecular mass of the gas? 1) ) ) ) Air consists of approximately 79% nitrogen and 19% oxygen. Which gas is less dense than air at STP? 1) CO 2 2) H 2 S 3) NH 3 4) SO 2 6. What is the molecular formula of a compound with an empirical formula of CH and a molecular mass of 78? 1) C 6 H 6 2) C 4 H 10 3) C 2 H 2 4) CH 7. A student determining the percent by mass of water in a hydrated crystal obtained the following data. Mass of crystal before heating g Mass of crystal after 1st heating g Mass of crystal after 2nd heating g What is the percent by mass of water hydrate? 1) 0.80% 3) 80.% 2) 0.20% 4) 20.% 8. The percent by mass of carbon in HC 2 H 3 O 2 is equal to 9. What is the percent by mass of oxygen in Ca(OH) 2 [formula mass = 47.1] 1) 21.6% 3) 45.9% 2) 43.2% 4) 54.1% 10. The percent by mass of nitrogen in N 2 O is 1) 8.0 3) 32 2) 16 4) A compound contains 50% sulfur and 50% oxygen by mass. The empirical formula of this compound is 1) SO 2) SO 2 3) SO 3 4) SO What is the molecular mass of a gas whose density is 1.25 grams per liter at STP? 1) ) ) ) An 8.24-gram sample of a hydrated salt is heated until it has a constant mass of 6.20 grams. What was the percent by mass of water contained in the original sample? 1) 14.1% 3) 32.9% 2) 24.8% 4) 75.2% 14. A 60. gram sample of LiCl H 2 O is heated in an open crucible until all of the water has been driven off. What is the total mass of LiCl remaining in the crucible? 1) 18 g 3) 42 g 2) 24 g 4) 60 g 15. What is the empirical formula of a compound that contains 30.4% nitrogen and 69.6% oxygen by mass? 1) NO 2) NO 2 3) N 2 O 3 4) N 2 O What is the percent by mass of hydrogen in CH 3 COOH (formula mass = 60.)? 1) 1.7% 3) 6.7% 2) 5.0% 4) 7.1% 17. A 1.20-gram sample of a hydrated salt is heated to a constant mass of 0.80 gram. What was the percent by mass of water contained in the original sample? 1) 20. 3) 50. 2) 33 4) A compound contains 16% carbon and 84% sulfur by mass. What is the empirical formula of this compound? 1) CS 2 2) C 2 S 2 3) CS 4) C 2 S 19. A hydrated salt is a solid that includes water molecules within its crystal structure. A student heated a 9.10-gram sample of a hydrated salt to a constant mass of 5.41 grams. What percent by mass of water did the salt contain? 1) 3.69% 3) 40.5% 2) 16.8% 4) 59.5%

2 20. What is the empirical formula of a compound consisting of 29.6% oxygen and 70.4% fluorine by mass? 1) OF 2) OF 2 3) O 2 F 4) O 2 F What is the molecular formula of a compound that has a molecular mass of 92 and an empirical formula of NO 2? 1) NO 2 2) N 2 O 4 3) N 3 O 6 4) N 4 O A sample of an unknown gas at STP has a density of 1.25 grams per liter. What is the gram molecular mass of this gas? 1) 28.0 g 3) 64.0 g 2) 44.0 g 4) 80.0 g 23. A compound has an empirical formula of CH 2 and a molecular mass of 56. What is its molecular formula? 1) CH 2 2) C 2 H 4 3) C 3 H 6 4) C 4 H The empirical formula of a compound is CH 2 O and the molecular mass is 180. What is the molecular formula of this compound? 1) C 6 H 12 O 6 2) C 4 H 8 O 4 3) C 2 H 4 O 2 4) CH 2 O 25. What is the percent by mass of nitrogen in the compound NH 4 NO 3 (formula mass = 80.)? 1) 5.7% 3) 29% 2) 18% 4) 35% 26. Which of the following gases has the greatest density at STP? 1) SO 2 2) CO 2 3) Cl 2 4) N What is the gram-molecular mass of a gas that has a density of 1.78 grams per liter at STP? 1) 17.8 g 3) 39.9 g 2) 22.4 g 4) 79.6 g 28. A compound consists of 25.9% nitrogen and 74.1% oxygen by mass. What is the empirical formula of the compound? 1) NO 2) NO 2 3) N 2 O 4) N 2 O Base your answer to the following question on the table below shows the data collected during the heating of a 5.0 gram sample of a hydrated salt. After 60. minutes, how many grams of water appear to remain in the salt? 1) ) 1.9 2) 2.0 4) What is the empirical formula of a compound that contains 85% Ag and 15% F by mass? 1) AgF 2) Ag 2 F 3) AgF 2 4) Ag 2 F In which compound is the percent by mass of oxygen greatest? 1) BeO 3) CaO 2) MgO 4) SrO 32. What is the percent by mass of sulfur in sulfur dioxide? 1) 32 3) 50. 2) 33 4) A compound has the empirical formula CH and a molecular mass of 78. What is the molecular formula of the compound? 1) C 2 H 2 2) C 3 H 3 3) C 4 H 4 4) C 6 H What is the percent by mass of oxygen in H 2 SO 4? [formula mass = 98] 1) 16% 3) 65% 2) 33% 4) 98% 35. The percent by mass of oxygen in H 2 C 2 O 4 is equal to

3 36. A compound which contains 75% carbon and 25% hydrogen by mass has the formula 1) CH 4 2) C 2 H 2 3) C 2 H 6 4) C 3 H Eleven grams of a gas occupies 5.6 liters at STP. What is the molecular mass of this gas? 1) 11 3) 44 2) 22 4) A compound was analyzed and found to contain 75% carbon and 25% hydrogen by mass. What is the compound's empirical formula? 1) CH 2) CH 2 3) CH 3 4) CH A 4.4 gram sample of a hydrate was heated until the water of hydration was driven off. The anhydrous compound remaining had a mass of 3.3 grams. What is the percentage by mass of water in the hydrate? 1) 25% 3) 67% 2) 33% 4) 75% 40. A 10.0 gram sample of a hydrate was heated until all the water of hydration was driven off. The mass of anhydrous product remaining was 8.00 grams. What is the percent of water in the hydrate? 1) 12.5% 3) 25.0% 2) 20.0% 4) 80.0% 41. At STP, what is the density of a gas that has a gram molecular mass of 32 grams? 1) 0.70 g/l 3) 3.2 g/l 2) 2.0 g/l 4) 1.4 g/l 42. What is the empirical formula of a compound that contains 28% iron, 24% sulfur, and 48% oxygen by mass? 1) FeSO 3 2) FeSO 4 3) Fe 2 (SO 3 ) 3 4) Fe 2 (SO 4 ) The density of a gas is 0.77 gram per liter at STP. What is the formula mass of the gas? 1) 8.5 g 3) 29 g 2) 17 g 4) 34 g 44. What is the approximate percent composition by mass of CaBr 2 (formula mass = 200)? 1) 20% calcium and 80% bromine 2) 25% calcium and 75% bromine 3) 30% calcium and 70% bromine 4) 35% calcium and 65% bromine 45. What is the ratio by mass of hydrogen to oxygen in H 2 O? 1) 1:2 3) 1:8 2) 2:1 4) 8:1 46. Which species contains the greatest percent by mass of hydrogen? 1) OH 2) H 2 O 3) H 3 O + 4) H 2 O 2

4 47. A hydrate is a compound with water molecules incorporated into its crystal structure. In an experiment to find the percent by mass of water in a hydrated compound, the following data were recorded: What is the percent by mass of water in the hydrate? 1) 8.0 % 2) 50. % 3) 72. % 4) 96. % 48. A student determining the percent by mass of water in a hydrated sample of salt obtained the following data: Mass of hydrate 6.25 g Mass of sample after 1st heating 5.12 g Mass of sample after 2nd heating 5.12 g The correct expression for obtaining the percent by mass of water in the sample is 49. A compound contains 53% Al and 47% O by mass. What is the empirical formula of this compound? 1) AlO 2) AlO 2 3) Al 2 O 3 4) Al 3 O The percent by mass of oxygen in Na 2 SO 4 (formula mass = 142) is closest to 1) 11% 3) 45% 2) 22% 4) 64%

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