Post-lab 6 Copper Cycle-solutions

Post-lab 6 Copper Cycle-solutions - choudhury (fac489)...

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choudhury (fac489) – Post-lab 6 Copper Cycle – lyon – (51155) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices before answering. 001 10.0 points Consider the process in which H 2 SO 3 is con- verted to H 2 SO 4 . The oxidation state of oxy- gen remains - 2, and the oxidation state of H remains +1. Select the correct statement. 1. S is reduced and loses electrons. 2. S is reduced and gains electrons. 3. S neither gains nor loses electrons in this reaction. 4. S is oxidized and gains electrons. 5. S is oxidized and loses electrons. correct Explanation: Oxidation numbers are per atom. The sum of oxidation numbers in a neutral molecule is zero and in a polyatomic ion is equal to the charge on the ion. We know the oxidation number of O is - 2. We use these values and set the sum of the oxidation numbers equal to the appropriate value. The oxidation number of S is symbolized by x : 2(+1) + x + 3( - 2) = 0 H 2 SO 3 : 2 + x - 6 = 0 x = +4 2(+1) + x + 4( - 2) = 0 H 2 SO 4 : 2 + x - 8 = 0 x = +6 Sulfur goes from +4 to +6 for a loss of two electrons. 002 10.0 points Determine the oxidation number of S in Na 2 SO 3 if the oxidation number of Na is +1 and O is - 2. 1. +4 correct 2. - 1 3. +1 4. - 4 5. +5 Explanation: To calculate oxidation numbers, remember that the the sum of the numbers must equal the total charge on the molecule or in the case of neutral species, zero. Let x be the oxidation number of S. 2(+1) + x + 3( - 2) = 0 Na 2 SO 3 : x - 4 = 0 x = +4 003 10.0 points Determine the oxidation state of Sn in SnO - 2 3 given the oxidation number of O = - 2. 1. - 2 2. +3 3. +6 4. +8 5. +4 correct Explanation: To calculate oxidation numbers, remember that the sum of the numbers must equal the total charge on the molecule or in the case of neutral species, zero. Sn x + 3(O - 2 ) = - 2 SnO - 2 3 : x + ( - 6) = - 2 x = 4 004 (part 1 of 3) 10.0 points Which of the following reactions (reactants only) in the copper cycle is a precipitation reaction? (Note that the reactants are not balanced in the equations below.)
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choudhury (fac489) – Post-lab 6 Copper Cycle – lyon – (51155) 2 1. Cu(OH) 2 (aq) + heat 2. CuO(s) + H 2 SO 4 (aq) 3. CuSO 4 (aq) + Al(s) 4. Cu(NO 3 ) 2 (aq) + NaOH(aq) correct Explanation: 005 (part 2 of 3) 10.0 points Which of the following is the solid produced from the precipitation reaction above? 1. CuSO 4 2. CuO 3. Cu(OH) 2 correct 4. Cu(NO 3 ) 2 Explanation: 006 (part 3 of 3) 10.0 points Which is a spectator ion in the precipitation reaction above? 1. Cu 2+ 2. OH - 3. Na + correct 4. SO 2 - 4 Explanation: Precipitation reactions are driven by the formation of a solid In the copper cycle, the soluble copper(II) nitrate reacts with sodium hydroxide to produce solid copper(II) hydrox- ide. The precipitation reaction in the copper cycle is as follows: Cu(NO 3 ) 2 (aq) + 2NaOH(aq) Cu(OH) 2 (s) + 2NaNO 3 (aq) (copper(II) hydroxide is the solid product) Cu 2+ (aq) + 2NO
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This note was uploaded on 12/13/2011 for the course CH 204 taught by Professor Leytner during the Fall '08 term at University of Texas at Austin.

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Post-lab 6 Copper Cycle-solutions - choudhury (fac489)...

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