sul1-2 - CHEMISTRY 1E03 Instructors: J. Barbier, R. Dumont...

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Version 1 Page 1 CHEMISTRY 1E03 10 OCTOBER 2008 Instructors: J. Barbier, R. Dumont MCMASTER UNIVERSITY - TERM TEST # 1 - DURATION: 100 minutes ANSWERS QUESTIONS 1–20 ARE WORTH 2 MARKS EACH. 1. The percentage by mass of bicarbonate in an Alka-Seltzer tablet is 32.5 %. Calculate the volume of carbon dioxide gas ( in mL ) generated at 37 °C and 1.00 atm from a 3.29 g tablet according to the reaction: HCO 3 (aq) + H + (aq) H 2 O(l) + CO 2 (g) A) 1370 B) 27.2 C) 446 2 marks D) 53 E) 618 A 3.29 g tablet contains 3.29 0.325 = 1.069 g bicarbonate Molar mass of bicarbonate (HCO 3 - ) = 12.01 + 1.008 + 48.00 = 61.018 g # moles bicarbonate = 1.069 / 61.018 = 1.752 10 –2 mole # moles of CO 2 produced = 1.752 10 –2 mole (see reaction above) PV = nRT V = 1.752 10 –2 0.08206 310.15 / 1.00 = 0.446 L = 446 mL
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Version 1 Page 2 2. Neutral atoms of 16 O, 17 O and 18 O all have: A) 8 electrons and 8 protons 2 marks B) 16 protons C) 16 protons and 16 electrons D) 8 neutrons and 8 protons E) 8 neutrons For all oxygen isotopes, Z = 8, i.e. there are 8 protons in the nucleus and 8 electrons in the neutral atoms. Isotopes differ by the number of neutrons only. 16 O has 8 protons and 8 neutrons in the nucleus, etc. 3. In a lab experiment, a student adds 10.0 mL of a 2.0 M solution of sodium hydroxide to 50.0 mL of a 0.30 M solution of cobalt(II) nitrate (where II represents the oxidation state of cobalt). When the reaction reaches completion, what mass (in grams) of cobalt(II) hydroxide is formed? Assume that the only reaction occurring is: Co(NO 3 ) 2 (aq) + 2 NaOH(aq) Co(OH) 2 (s) + 2 NaNO 3 (aq). A) 3.9 B) 1.9 C) 2.9 D) 0.93 2 marks E) 1.4 0.5 mark answer obtained if 0.015 mole Co(OH) 2 is used in the calculation # moles of NaOH = volume molarity = 0.01 2 = 0.02 mole # moles of Co(NO 3 ) 2 = volume molarity = 0.05 0.3 = 0.015 mole For a complete reaction, 0.015 mole Co(NO 3 ) 2 would require 0.03 mole NaOH (see coefficients in the balanced reaction). Hence NaOH is the limiting reagent. 0.02 mole NaOH react with 0.01 mole Co(NO 3 ) 2 to form 0.01 mole Co(OH) 2 . Mass of Co(OH) 2 formed = # moles molar mass = 0.01 (58.93 + 32 + 2.016) = 0.93 g
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Version 1 Page 3 4. The density of a noble gas is 2.71 g L –1 at 3.00 atm and 0 °C. What is the gas? A) Xe B) Kr C) He D) Ar E) Ne 2 marks Assume that the gas is ideal PV = nRT V = sample mass / density = # moles molar mass / density = n M / d PV = P n M/d = nRT M = RT d/ P = 0.08206 273.15 2.71 / 3.00 = 20.2 g the noble gas is Ne 5. Which one of the following statements is false regarding reactions (i), (ii) and (iii), shown here? (i) 2NaOH(aq) + NiCl
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sul1-2 - CHEMISTRY 1E03 Instructors: J. Barbier, R. Dumont...

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