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chemistry ch2071a teacher-marked assignment oxidation-reduction chemistry student instructions Overview This assignment is designed to give you practice in demonstrating your understanding of the fundamental concepts of chemistry. It is not for NCEA credit, but it will help you to develop your skills, so that you do well in future assessments. Conditions • This is a closed book assessment; you may not refer back to any booklets. • There is no time limit for this assignment, but allow about one hour to finish it. You will need: • a pen or pencil and a calculator. If you do not understand any of these conditions, please phone, fax or email your teacher now. A Periodic Table and tables of species and their colours are supplied near the back of this assignment. You can tear out this page to refer to the tables more easily. Supervisor requirements You and your supervisor (if applicable) must sign the cover sheet at the back of the assessment to verify that the work is your own. Assessment criteria Not Attempted Did not attempt to complete. Not yet on target for Achieved Did not demonstrate an understanding of oxidationreduction chemistry. On target for Achieved Demonstrated an understanding of oxidationreduction chemistry. On target for Achieved with Merit On target for Achieved with Excellence Demonstrated an in-depth understanding of oxidationreduction chemistry. Demonstrated a comprehensive understanding of oxidationreduction chemistry. For teacher use only © te aho o t e k ur a p o un a m u 2012/2 ch2071a teacher-marked assignment answer all the questions question one a. Complete the table with the oxidation number of each underlined element. The first one has been done for you. Species NH3 Oxidation number -3 H2SO4 Cl2 NO3- HCl b. The reaction between magnesium and hydrochloric acid is represented by the following equation: Mg + 2HCl MgCl2 + H2 Identify the oxidant in this reaction. Explain your answer with reference to oxidation numbers. 2 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment c. For each of the following reactions, identify the underlined product, the oxidant and the reductant. i. Chlorine gas is bubbled through a colourless potassium bromide solution, turning it yellow-orange. product oxidant reductant ii. When hydrogen peroxide is added to an acidified potassium permanganate solution, the purple solution becomes colourless and bubbles of gas are seen. product oxidant reductant iii. When zinc is added to an iodine solution, the brown solution becomes colourless. product oxidant reductant iv. When aluminium foil is added to bromine liquid, the mixture burns and white smoke is produced. product oxidant reductant © te ah o o t e k ur a p o un a m u CH2071A 3 ch2071a teacher-marked assignment question two a. Sulfur dioxide gas (SO2) is bubbled through a solution of acidified potassium permanganate (KMnO4). An oxidation-reduction reaction occurs. The unbalanced equation for this reaction is: MnO4– + SO2 Mn2+ + SO42– A student wrote the two following half-equations: Mn2+ + 4H2O Equation One MnO4– + 8H+ + 5e– + – SO42– + 2H2O Equation Two SO2 + 4H + 2e It is not possible to combine these two half-equations as the student had written Equation Two incorrectly. 4 i. Describe the mistake that was made in Equation Two. ii. Write Equation Two correctly. iii. Discuss, in terms of oxidation-reduction principles, electron transfer and charge, why Equation One and the original Equation Two cannot be combined into an overall balanced equation. CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment b. Hydrogen peroxide is added to a solution of potassium bromide. You may use the resource tables given at the end of this assignment to help you answer the following questions. i. Identify which substance is being reduced. Use oxidation numbers and the transfer of electrons to justify your choice. ii. Describe what you would expect to observe for this reaction. Link all observations to the species concerned. (Tip: remember to describe both reactants and products.) iii. Write the balanced oxidation half reaction. iv. Write the balanced reduction half reaction v. Write the full balanced equation. © te ah o o t e k ur a p o un a m u CH2071A 5 ch2071a teacher-marked assignment question three Acidified potassium dichromate, K2Cr2O7, is a common oxidant used in aqueous solution. You may use the resource tables given at the end of this assignment to help you answer the following questions to explain the chemistry when acidified potassium dichromate solution is added to a solution of potassium iodide, KI. a. Describe what you would expect to observe for this reaction. Link all observations to the species concerned. (Tip: remember to describe both reactants and products.) b. Write the balanced oxidation half reaction. c. Explain why this is the oxidation half reaction. Refer to changes in oxidation number and the number of electrons transferred. d. Write the balanced reduction half reaction. e. Explain why this is the reduction half reaction. Refer to changes in oxidation number and the number of electrons transferred. f. Write the full balanced equation. 6 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment question four: Drops of iron(II) sulfate are added to a chlorine solution. The very pale green solution began to turn colourless. You may use the resource tables given at the end of this assignment to help you answer the following questions. a. Describe what you would expect to observe for this reaction. Link all observations to the species concerned. (Tip: remember to describe both reactants and products.) b. Write the balanced oxidation half reaction. c. Explain why this is the oxidation half reaction. Refer to changes in oxidation number and the number of electrons transferred. d. Write the balanced reduction half reaction. e. Explain why this is the reduction half reaction. Refer to changes in oxidation number and the number of electrons transferred. f. Write the full balanced equation. © te ah o o t e k ur a p o un a m u CH2071A 7 ch2071a teacher-marked assignment Extra space. Label each question clearly. 8 CH2071A © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment appearance of redox reactants and their products redox reactants and their products Species Appearance Br2 → Br– Br– colourless ion Cl2 → Cl– Br2 red/orange liquid C black solid CO2 → C → Cr3+ CO2 colourless gas which turns lime water milky Cr2O /H Cu2+ → Cu Cl– colourless ion Fe3+ → Fe2+ Cl2 pale green gas H+ → H2 Cr2O72–/H+ orange ion H2O2 → H2O Cr3+ green ion HNO3(conc) → NO2 Cu Pinkish/red-brown solid I2 → I– Cu2+ blue ion IO3– → I2 Fe pale green ion MnO /H → Mn2+ Fe3+ orange (brownish) ion → H colourless ion O2 H2O2 + → O2– H2 colourless gas O2 OCl– → Cl– H2O colourless liquid H2O2 colourless liquid S H2S colourless gas HNO3(conc) colourless liquid HSO colourless ion I colourless ion I2 brown solution, black solid 2+ – 3 – – 4 + → H2S 2– 4 SO → HSO3– SO42– → SO2 SO → SO32– 2– 4 colourless ion IO3– colourless ion Mn 2+ MnO /H purple ion NO2 brown gas O2 colourless gas 2– O colourless ion OCl– colourless ion S yellow solid SO2 colourless gas SO32– colourless ion SO42– colourless ion Zn colourless ion – 4 2+ + 2– 7 + © te ah o o t e k ur a p o un a m u CH2071A 9 10 CH2071A Y 226 223 262 261 262 105 263 264 107 265 108 268 109 192 77 Ir 103 45 Rf Db Sg Bh Hs Mt 106 104 103 88 190 87 Fr Ra Lr 186 184 181 179 175 137 76 133 75 101 W Re Os 74 98.9 56 73 95.9 44 55 72 92.9 43 58.9 195 78 197 79 108 47 63.6 201 80 112 48 65.4 204 81 115 49 69.7 Pt Au Hg Tl 106 46 58.7 31 Zr Nb Mo Tc Ru Rh Pd Ag Cd In 91.2 42 Cs Ba Lu Hf Ta 71 88.9 41 55.8 28 30 87.6 Rb Sr 40 54.9 27 Si P 207 82 Pb 119 209 83 Bi 122 51 74.9 33 31.0 S Cl 210 84 I 210 85 127 53 79.9 35 35.5 17 19.0 9 F 17 Ar Kr 222 86 131 Xe 54 83.8 36 40.0 18 20.2 10 Ne 4.0 He Po At Rn 128 52 79.0 34 32.1 16 16.0 8 O 16 Sn Sb Te 50 72.6 32 28.1 15 14.0 7 N 15 Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br 52.0 26 29 85.5 12 39 11 38 V 50.9 25 10 37 Ti 47.9 24 9 45.0 Ca Sc 23 7 8 40.1 K 22 6 39.1 21 5 20 4 19 3 Al 27.0 24.3 23.0 14 13 Na Mg 12.0 6 C 14 10.8 12 1.0 11 Molar mass/g mol-1 5 B 9.0 1 H 6.9 Atomic Number Be 4 3 13 Li 2 1 2 18 ch2071a teacher-marked assignment periodic table © te ah o o te k u ra p ou n a mu ch2071a teacher-marked assignment what to do next When you have finished this teacher-marked assignment, please make sure that you have written your name and ID number on the back cover. You can also use a label if you have one on hand. By post: Put the assignment in the plastic envelope provided. Make sure that the address card shows the address for Te Aho o Te Kura Pounamu. Seal the envelope with tape before you post it. Do not include booklets from other subjects with this Science work. By email: Scan the pages including the cover sheet and email to your teacher. The standard format for Te Kura teacher email addresses is: firstname.lastname@tekura.school.nz If you aren’t sure who your teacher is, call 0800 65 99 88. If you do not have your next set of study materials, contact your teacher immediately. If you are not sure what to do next, ask your teacher for advice. © te ah o o t e k ur a p o un a m u CH2071A 11 cover sheet – ch2071a students – place student address label below or write in your details. Full Name ID No. Address (If changed) authentication statement I certify that the assessment work is the original work of the student named above. Signed Signed (Student) (Supervisor) for school use only assessment www.tekura.school.nz Copyright © 2012 Board of Trustees of Te Aho o Te Kura Pounamu, Private Bag 39992, Wellington Mail Centre, Lower Hutt 5045, New Zealand. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the written permission of Te Aho o Te Kura Pounamu.
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