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Redox module 3 word 97
- 1. 1 NAME………………………………………..CLASS………….TEACHER……………… Question 1 a) State the conditions for the rusting of iron i) …………………………………..ii)………………………………. b) What is the meaning of corrosion of metals? K Na ……………………………………………………………………………………… Mg Al Zn Write a half equation for corrosion of zinc metal ……………………………….. Fe c) Can corrosion of zinc be called rusting of zinc? Explain Sn Pb Cu Hg Ag Au
- 2. 2 …………………………………………………………………………….. d) Iron rusts faster at places near the sea. Explain ………………………………………………………………. e) In the diagram to the right are the metals arranged in descending order in electrochemical series. Gold when left for a long time does not corrode , whereas magnesium corrodes easily. Explain. ……………………………………………………………………….. f) Aluminum is situated high in the electrochemical series. But aluminum is very resistant to corrosion as compared to iron. Explain ……………………………………………………………………………….. Fill in the blanks with suitable words
- 3. 3 Step 1 (Oxidation)The surface of iron in the middle of water droplet serves as the anode, where oxidation occurs. a) What happens to the iron atom here? ………………………………………………………………. b) Write the half equation for the reaction that occur in a) above ………………………………………………………………………………… c) Through what substance do the electrons move to? ……………………… d) Through what substance do the iron(II) ions move to? ………………………. Step 2 (Reduction) the Iron surface serves as cathode where reduction occur e) Where do the electrons that are released by iron flow to? And why?
- 4. 4 ……………………………………………………………………………… f) What happens to the electrons here? ……………………………………………………………………. g) Write the half equation for the reaction that occur …………………………………………………………………… h) Where do the hydroxide ions formed in this reaction go to? ………………………………………………………………………… Step 3 Formation of Voltaic Cell) a) What happens to the iron(II) ions and the hydroxide ions formed from step 1 and step 2? ………………………………………………………………………… b) Write the ionic equation for the reaction …………………………………………………………………………. c) A voltaic cell is formed in this mechanism of rusting. State 2 process that produce this voltaic cell i) Through the metal ………………………………………………… ii) Through the water ………………………………………………….. Step 4 Formation of rust a) What happens to the iron(II) hydroxide formed when exposed to oxygen? ………………………………………………………………………… b) Write the formula of the rust formed …………………………………………………………………………. c) State the oxidizing agent and the reducing agent in rusting mechanism ……………………………………………………………………………..
- 5. 5 Fill in the table below . You may choose answers from the box given Iron and steel objects, like motorcars, ships, Cans of food bridges and steel pipes In machinery Bumpers of Roofs of houses Blocks of zinc are attached to motorcars the hull of the ship To protect underground Knives, spoons, medical instruments, steel pipelines kitchen sinks Ways to Methods Where are the method used? control rusting 1 Using Covering with paint 2 protective 3 coating 4 Covering with oil and grease 5 Covering with tin(tin plating) Covering with chromium(chromium plating) Covering with zinc metal(galvanizing) 6 Sacrificial Using blocks of zinc metal 7 protection Using blocks of magnesium metal 8 Alloying Making stainless steel (alloy)
- 6. 6 An experiment was done in a lab to investigate factors that affect rust. All the boiling tubes were left for 3 days a) After 3 days, it was noticed that in boiling tubes C and D, the potassium hexacyanoferrate(III) solution changed colour to dark blue. What is the inference? ………………………………………………………………. b) In which boiling tubes did iron nails show rusting? ………………………………………………………….. c) The nails in boiling tubes A and B did not rust. Explain ………………………………………………………………… d) Explain the function of experiment in E …………………………………………………………………….. e) Write half reaction for i) Oxidation in experiment A ……………………………………. ii) Oxidation in experiment C ……………………………………
- 7. 7 iii) Oxidation in experiment E …………………………………… f) What type of metals prevent rusting of iron? ………………………….. g) What type of metals encourage rusting of iron?.............................. h) If iron nails are immersed in alkaline solution, the nails do not rust. Explain ………………………………………………………………………. i) Calcium is more effective than zinc to prevent rusting Why do you think steel objects are coated with zinc instead of calcium? …………………………………………………………………………. j) Explain the followings i) When a metal corrodes, it undergoes oxidation ………………………………………………………………… ii) In tin plating, iron can is coated with tin. However as soon as the can is scratched, rusting will occur quickly ………………………………………………………………………. iii) In galvanizing, iron is coated with a layer of zinc. When the galvanized iron is scratched, rusting does not occur.
- 8. 8 ……………………………………………………………………. Question 1. What is meant by reactivity series of metals? ……………………………………………………………………………………. Question 2. Arrange the following metals according to the reactivity series, in descending order …… Aurum, silver, carbon potassium, magnesium, … hydrogen , sodium, mercury, aluminum, zinc, …… copper, lead, iron, tin …. …… … …… …. …… … …… … …… … …… …. Question 3 Which substances react with each other? If the substances react, write chemical equations a) Na2O + Mg ………………………………………………………. b) Mg + CuO ………………………………………………………. c) C + PbO ………………………………………………………….. d) H2 + ZnO …………………………………………………………
- 9. 9 e) Fe + Ag2O ………………………………………………………… f) CaO + Zn …………………………………………………………… Question 4 Table of extraction of metals K These metals have very strong attraction towards oxygen, therefore the Na oxides cannot be reduced by Carbon Ca Mg Extraction of metals must be done by electrolysis of molten compounds Al C Zn These metals have weak attraction towards oxygen compared to carbon, so the ores can be extracted easily by carbon H Fe Reactivity Sn increases Pb Cu Weak attraction towards oxygen, therefore heating the oxides in air Hg can reduce the metals easily Ag Very weak attraction towards oxygen. Exist as free metals Au How are these metals extracted from their ores? Use the table above to help you a) Zinc from zinc sulphide ………………………………….. b) Iron from iron(III) oxide ………………………………….. c) Copper from copper(II) sulphide ………………………….. d) Aluminum from aluminum oxide …………………….. e) Tin from tin(IV) oxide ………………………………… f) Gold and silver ………………………………………….. Question 5 Zinc is below magnesium in the reactivity series. Can zinc be extracted from zinc oxide using magnesium? Explain ……………………………………………………………………………………… Question 6 Why is carbon the preferred element used to reduce metals and not hydrogen or other metals?
- 10. 10 ………………………………………………………………………………………………….. Question 1 Complete the table below for differences between electrolytic cell and chemical cell Electrolytic cell Chemical cell/voltaic cell Draw Diagram Example for Example for Electrolysis of copper(II) sulphate Voltaic cell using copper and zinc as using carbon electrode electrodes, and copper(II) sulphate and zinc sulphate as electrolytes ………………………………. …………………………………….. Presence of voltmeter or ammeter? And ……………………………………… …………………………………….. why? Change of energy Positive electrode Negative Positive electrode Negative electrode electrode Type of electrode Electrode that is Electrode that is Less More joined to the joined to the electronegative electronegative …….. part of the …….. part of the metal becomes + battery battery electrode metal becomes - electrode Oxidation occur at ( release e-) and write half equation Reduction occur at (accept e-) and write half equation Cathode (area where electrons are accepted) Anode (area where electrons are released)