Download NotesDownload Redox Reactions NotesDownload Reversible Reactions Notes (Credits to Mustafa Asif) Download presentation here Additional NotesREDOX ReactionBoth oxidation and Reduction going on side-by-side Combustion Oxidation that occurs so rapidly that noticeable heat and light are produced; burning. Incomplete combustion
Carbon monoxide
Carbon Essentially carbon acts as a reducing agent as well as the carbon monoxide that is inevitably formed by its heating in air.
DEFINITIONS OF OXIDATION AND REDUCTION (REDOX)
Oxidation State in Reduction-Oxidation reactionOxidation State is the charge an atom would have if it existed as an ionTo work out oxidation state, the rules are:
Work out the oxidation states of the underlined elements in these compounds: (a) CO2 (oxidation state of C) + (-2) x 2 = 0 (oxidation state of C) + (-4) = 0 Oxidation state of C = +4 (b) KMnO4 (+1) + (oxidation state of Mn) + (-2) x 4 = 0 (oxidation state of Mn) + (+1) + (-8) = 0 (oxidation state of Mn) + (-7) =0 Oxidation state of Mn = +7 (c) Fe(NO3)2 (oxidation state of Fe) + (-1) x 2 = 0 (oxidation state of Fe) + (-2) = 0 Oxidation state of Fe = +2 Examples of elements with variable oxidation statesSome compounds with possible variable oxidation states have roman numeral as a guide about their oxidation state, e.g.
A. Metals with acids Cu (s) + HCl (aq) → CuCl2 (aq) + H2 (g)
Cl2 (aq) + 2KI (aq) → 2KCl (aq) + I2 (aq)
Test for Oxidising/Reducing AgentsNon-Redox Reactions
Reversible Reactions
Effect of Temperature on Reversible Reactions
Effect of Pressure on Reversible Reactions
Dynamic equilibrium
MCQ Questions1. Which one of the following is usually described as a reducing
agent?
b. concentrated sulphuric acid c. copper(II) oxide d. Sodium oxide
2. Cu+ ions
may be formed when
3. An oxidisng agent was observed to turn from orange to green. It
is most likely to be:
4. When iron
(II) oxide is heated strongly with carbon
5. When iron
(III) sulphate is reduced to iron (II) sulphate, the colour of the solution
turns from a. Cl2 + 2I- –> 2Cl- + I2
7. Which conversion involves the smallest change in oxidation number of the
underlined element?
8. The oxidation states of chlorine in ClO4- and Cl2O are respectively
9. Which
statement is true about oxidizing agents?
10. What
does an oxidizing agent do? 11. When zinc reacts with dilute sulphuric acid a gas is released. What happens to the zinc and what is the gas released?
12. Which compound, when added to aqueous iron(II) sulphate, takes part in a redox reaction? a. ammonia b. barium chloride c. potassium manganate(VII) d. sodium hydroxide 13. Which of the following is a property of aqueous potassium iodide? a. it does not conduct electricity b. it is decolorised by chlorine c. it reacts with aqueous bromine to form iodine d. it is a purple solution 14. What happens when a copper atom becomes a copper(II) ion? a. it is oxidised by losing two electrons b. it is oxidised by gaining two electrons c. it is reduced by gaining two electrons d. it is reduced by losing two electrons 15. Which reaction is an example of a redox reaction? a. CuO + H2SO4 --> CuSO4 + H2O b. H+ + OH- --> H2O c. Ag+ + Cl- --> AgCl d. 2SO4 + O2 --> 2SO3 16. In which pair is the underlined element in the same oxidation state in both compounds? a. CuCl2 and NaCl b. H2S and SO2 c. Fe2O3 and FeSO4 d. MnO2 and MnCl2 17. Solution X turns acidified potassium dichromate(VI) from orange to green. What must solution X contain? a. an alkali b an ammonium salt c. an oxidising agent d. a reducing agent 18. In which oxide does X have the same oxidation state as in the chloride, XCl3? a. X3O b. X2O c. XO2 d. X2O3 19. In which of the following changes is the nitrogen reduced? a. NH3 to NO b. NH3 to NO3- c. N2 to NH3 d. N3- to N2 20. When gas X is passed over heated copper(II) oxide the products are copper and steam only. What is gas X? a. ammonia b. carbon monoxide c. hydrogen d. methane 21. Which element in the reaction below is oxidised? 2FeSO4 + Cl2 + H2SO4 --> Fe2(SO4)3 + 2HCl a. chlorine b. hydrogen c. iron d. sulphur 22. In which reaction does the oxidation state of iron remain unchanged? a. 2Fe + 3Cl2 --> 2FeCl3 b. 2FeCl2 + Cl2 --> 2FeCl3 c. Fe + 2FeCl3 --> 3FeCl2 d. Fe2O3 + 6HCl --> 2FeCl3 + 3H2O 23. Titanium is manufactured from a mixture of iron(II) titanate, FeTiO3, and iron(III) titanate, Fe(TiO3)3. What are the oxidation numbers of titanium in these 2 compounds? a. +2, +2 b. +4, +4 c. +2, +3 d. +4, +2 24. Which of the following does not represent a redox reaction? a. Sn2+ (aq) + 2Fe3+ (aq) ---> Sn4+ (aq) + 2Fe2+ (aq) b. Ca (s) + 2HCl (aq) ---> CaCl2 (aq) + H2 (g) c. Ag+ (aq) + Cl- (aq) ---> AgCl (s) d. Zn (s) + 2H+ (aq) ---> Zn2+ (aq) + H2 (g) 25. In which pair is the underlined element in the same oxidation state in both compounds? a. CuCl2 and NaCl b. H2S and SO2 c. Fe2O3 and FeSO4 d. MnO2 and MnCl2 26. Which compound, when added to aqueous iron(III) sulphate, takes part in a redox reaction? a. ammonia b. barium chloride c. potassium manganate (VII) d. sodium hydroxide 27. Solution X turns acidified potassium dichromate(VI) from orange to green. What must solution X contain? a. alkali b. ammonium salt c. oxidising agent d. reducing agent Answers1. a2. b 3. b 4. a 5. d 6. d (CuO + H2 –> Cu + H2O) 7. b (NO3- (aq) –> NO2 (g)) 8. c (+7 and +14) 9. d (They readily accept electrons) 10. d (It turns aqueous potassium iodide brown) 11. a 12. c 13. c 14. a 15. d (the oxidation number of S increased from +4 in SO2 to +6 in SO3. The oxidation number of oxygen decreased from 0 in O2 to -2 in SO3) 16. a (the oxidation state of chlorine in both is -1) 17. d 18. d 19. c 20. c (H2 reduces CuO to Cu while itself is oxidised to H2O) 21. c 22. d (the oxidation number of Fe in iron(III) oxide and iron(III) chloride is +3) 23. b 24. c 25. a (both have an oxidation state of -1) 26. c (this is a good oxidising agent in an acidic medium) 27. d Structured Questions1a. What is the meaning of (II) in copper(II) oxide1b. In each of the following, underline the formula of the substance that is being oxidised. Give a reason in each case. i. 2CO + O2 ---> 2CO2 ii. 2NH3 + 3CuO ---> N2 + 3Cu + 3H2O iii. 2Fe2+ + Cl2 ---> 2Fe3+ + 2Cl- Solution 1a. It refers to the valency of the metal copper 1bi. 2CO + O2 --> 2CO2 reason: addition of oxygen to the compound 1bii. 2NH3 + 3CuO --> N2 + 3Cu + 3H2O reason: removal of hydrogen from the compound 1biii. 2Fe2+ + Cl2 --> 2Fe3+ + 2Cl- reason: increase in valency from +2 to +3 for the iron ion 2a. Define oxidation in terms of electron transfer 2b. Name a substance which is an oxidizing agent in aqueous solution. Explain how aqueous potassium iodide can be used to confirm that this named substance is an oxidizing agent. Solution 2a. Oxidation is the transfer of electron from one particle to another. The particle that loses the electron is said to be oxidised. 2b. Chlorine is an oxiding agent. Aqueous chlorine is added to aqueous potassium iodide with starch added. A dark blue color is seen, indicating the presence of I2. So I- must have been oxidised to I2. 3. Name 5 different salts which can be prepared using only the substances dilute sulphuric acid, dilute ethanoic acid, aqueous ammonia and potassium hydroxide. Solution - potassium sulphate - potassium ethanoate - ammonium sulphate - ammonium ethanoate - potassium hydrogensulphate 4. By giving either the name or the formula, identify each of the lettered substances in the following: a. when an excess of aqueous chlorine was added to aqueous potassium iodide, a black solid, P was formed. What is P? b. Q is a sodium salt. When a solution of Q was added to aqueous silver nitrate, a white precipitate, R was formed. This precipitate did not dissolve in dilute nitric acid. What is Q and R? c. S is a sodium salt. When a solution of S was added to aqueous barium nitrate, a white precipitate, T was formed. When dilute nitric acid was added to T, it dissolved and a gas, U which turned limewater milky was evolved. What is S, T, and U? d. When aqueous sodium hydroxide was added to aqueous zinc chloride, a white precipitate, V was formed. This precipitate dissolved in an excess of sodium hydroxide to form a colorless solution in which zinc was present as a salt, W. What is V and W? Solution 4a. P = iodine, I2 Cl2 oxidises I- to I2. Cl2 + 2I- --> 2Cl- + I2 4b. Q = sodium chloride, NaCl R = silver chloride, AgCl Cl- + Ag+ --> AgCl 4c. S = sodium carbonate, Na2CO3 T = Barium carbonate, BaCO3 U = carbon dioxide, CO2 Since the white precipitate dissolves in dilute HNO3, the anion cannot be SO42- because BaSO4 is insoluble in dilute HNO3 Ba2+ + CO32- --> BaCO3 BaCO3 + 2H+ --> Ba2+ + H2O + CO2 4d. V = zinc hydroxide, Zn(OH)2 W = sodium zincate, Na2Zn(OH)4 or Na2ZnO2 Zn2+ + 2OH- --> Zn(OH)2 Zn(OH)2 + 2OH- --> Zn(OH)42- or ZnO22- + 2H2O 5. Aqueous copper(II) sulphate reacts with aqueous potassium iodide according to the equation below. 2Cu2+ + 4I- --> 2CuI + I2 a. Identify the reducing agent in this reaction. Explain your answer b. Describe briefly how acidified potassium manganate(VII) can be used to test for a reducing agent Solution 5a. Aqueous potassium iodide. Iodide ion gives away electrons and become oxidised to iodine molecules. The oxidation state of iodine increased from -1 in I- to 0 in I2 indicating that iodide is oxidised. b. Addition of purple acidified potassium manganate(VII) solution to a reducing agent causes the purple solution to decolorise. 6. Aqueous iron(II) ions react with acidified potassium manganate(VII) according to the equation below 5Fe2+ + 8H+ + MnO4- --> 5Fe3+ +4H2O +Mn2+ a. What is the reducing agent in this reaction? Explain your answer. b Briefly describe how aqueous potassium iodide can be used to test for an oxidising agent Solution 6a. Iron(II) irons, Fe2+ is the reducing agent. Each Fe2+ ion has lost 1 electron to form Fe3+ ion causing the oxidation number of iron to increase from +2 to +3 b. Add the oxidising agent to potassium iodide solution. A brown solution of iodine is obtained. 7. Potassium dichromate is an oxidizing agent. The oxidation number of chromium in potassium dichromate is +6. ai. name one compound which can be oxidized by potassium dichromate aii. state the condition(s) under which the compound reacts with potassium dichromate aiii. what product is formed from the compound in the redox reaction? b. In the presence of a dilute acid, chromium(II) ions react with atmospheric oxygen to from chromium(III) ions and water. bi. write the half equations for the formation of chromium(III) ions bii. write the half equation for the formation of water biii. write the overall equation for the reaction c. suggest 2 ways in which chromium can be used to prevent the corrosion of iron. Solution ai. potassium iodide OR iron(II) sulphate aii. mix the potassium iodide with acidified potassium dichromate OR mix the iron(II) sulphate with acidified potassium dichromate aiii. iodine OR iron(III) ions bi. Cr2+ --> Cr3+ + e- bii. O2 + 4H+ + 4e- --> 2H2O biii. 4Cr2+ + O2 + 4H+ --> 4Cr3+ + 2H2O c. chromium can be used in chromium-plating and making stainless steel. iodide ions are oxidised to brown iodine molecules. |
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