exam 2 - Garg Pallavi – Exam 2 – Due Nov 7 2007 11:00...

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Unformatted text preview: Garg, Pallavi – Exam 2 – Due: Nov 7 2007, 11:00 pm – Inst: Donna C Lyon 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points What is the reducing agent in the reaction 4NH 3 (g) + 3O 2 (g) → 2N 2 (g) + 6H 2 O(g)? 1. O 2 2. NH 3 correct 3. N 2 4. H 2 O Explanation: The reducing agent causes another sub- stance to be reduced by donating the elec- trons gained by the reduced substance. The reducing agent therefore loses electrons and is oxidized. Oxidation is indicated by the algebraic in- creaseoftheoxidationnumber. Theoxidation number of free, uncombined elements is zero. This includes polyatomic elements such as N 2 and O 2 . The sum of oxidation numbers in a neutral molecule is zero. The oxidation num- bers of O and H in compounds are- 2 and +1 respectively. We can calculate the oxidation number of N in NH 3 : x + 3(+1) = 0 NH 3 : x =- 3 The oxidation number of N increases from- 3 to 0, indicating that it is being oxidized and is the reducing agent. 002 (part 1 of 1) 10 points Dissolving 3.00 g of an impure sample of cal- cium carbonate in hydrochloric acid produces 0.656 L of carbon dioxide, measured at 293 Kelvin and 1.04 atm. What is the percent by mass of the calcium carbonate in the sam- ple? (Hydrochloric acid reacts with calcium carbonate to produce calcium chloride, water, and carbon dioxide). 1. 54.6 percent 2. 88.2 percent 3. 76.3 percent 4. 94.7 percent correct 5. 64.5 percent Explanation: 003 (part 1 of 1) 10 points Write the net ionic equation for the follow- ing reaction: Aqueous solutions of copper(II) nitrate and sodium hydroxide are mixed to form solid copper(II) hydroxide and aqueous sodium nitrate. 1. 2Na + + 2NO- 3 → 2NaNO 3 (aq) 2. Cu 2+ + 2NO- 3 + 2Na + + 2OH- → Cu 2+ + 2OH- + 2Na + + 2NO- 3 3. Cu 2+ + 2OH- → Cu(OH) 2 (s) correct 4. Cu(NO 3 ) 2 (aq) + 2NaOH(aq) → Cu(OH) 2 (s) + 2NaNO 3 (aq) Explanation: In a net ionic equation, only the species involved in the reaction are written. All spec- tator ions are removed. Sodium ions (Na + ) and nitrate ions (NO- 3 ) appear on both sides of the total ionic equation, so they are specta- tor ions and are not written. Remember that sodium ions and nitrate are common specta- tor ions. 004 (part 1 of 1) 10 points For the following reaction, 2HCl + Na 2 CO 3 → 2NaCl + H 2 O + CO 2 4 . 5 L of CO 2 is collected at STP. What is the molarity of HCl solution if 245 mL was used up? The molar mass of Na 2 CO 3 is 106 g / mol, the molar mass of HCl Garg, Pallavi – Exam 2 – Due: Nov 7 2007, 11:00 pm – Inst: Donna C Lyon 2 is 36 . 5 g / mol, and the density of the solution is 1 . 23 g / mL....
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exam 2 - Garg Pallavi – Exam 2 – Due Nov 7 2007 11:00...

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