Name Class: ____ Date; ____ _ Metals @answer iv rica Go through the worked example. Use the tips to gui the questions. you in understanding and answering vr seideug Jo} QT JeBYS4OM (a) Brass is an alloy of copper and zinc. Explain why brass is harder than pure copper. Thought Process The physical properties of a substance depend on its structure. The difference in hardness between brass (an alloy) and copper (a metal) is due to their different atomic arrangements. Answer The atoms in pure copper are packed regularly in layers. When a force is applied, the layers of atoms can slide over one another easily. Thus, pure copper is soft. In brass, the copper and zinc atoms are of different sizes. This breaks up the regular arrangement of atoms in pure copper, which makes it harder for the layers to slide over one another when a force is applied. Hence, brass is harder than pure copper. ‘= It is @ common mistake to think that brass (an alloy) is harder and stronger than copper (a pure metal) because copper forms strong bonds with zinc. ‘+ The hardness of an alloy is due to the different sizes of the constituent atoms of the alloy. (b) Explain the electrical conductivity of zinc in the solid state. ‘Thought Process The electrical conductivity of a substance depends on its type of chemical bonding and its physical state. Answer Zinc is a metal. Zinc atoms are held by metallic bonds, which consist of positive zinc ions surrounded by a ‘sea of mobile electrons’. This means that the outer electrons are free to move through the entire metal structure. Thus, zinc can conduct electricity in the solid state. ‘+ Itis too vague to write ‘metals conduct electricity because the electrons move through the entire metal structure’. ‘+ Note that metals conduct electricity due to the movement of their outer electrons only. © 2014 Marshall Cavendish Education Pte Ltd Workshest10 75(ce) Carbon steels are alloys of iron and carbon. How does the carbon content of steel affect the properties of steel? Thought Process Whether a steel is malleable or brittle will depend on the proportion of carbon in the steel. Answer Mild steel has low carbon content. It is strong and malleable. High-carbon steel has high carbon content. It is strong but brittle, Thus, the higher the content of carbon, the more brittle the steel, This is @ question on comparing the different physical properties of high-carbon steel and mild steel (low-carbon stee!). TEST Section A: [Mun oni teas Choose the correct answer and write its letter in the brackets provided. 4. What is an alloy? A mixture of a metal with one or a few other elements. A mixture of a non-metal with one or a few other elements A mixture that must contain carbon ‘A mixture that must contain iron Cc vom> 2. Which diagram shows the structure of an alloy? HO " Po% @0o O° SC Cay 3. What are the advantages of recycling metals? 1 Conserves fossil fuels, 2 Reduces air and water pollution 3 Always requires less time and money A tand2 B tand3 © 2and3 D 1,2and3 ca TE Worksheet 10 (© 2014 Marshall Cavendish Education Pte LidThe positions of some metals in the reactivity series are shown below. Most reactive aye In which beaker will there be no reaction? A so B - PrxNO,on) sncliag) > Least reactive > lead => silver 2 E c E AgNOJaa) soci) ( Which statement about the production of iron from ironi{ll) oxide in the blast furnace is correct? com> Calcium carbonate (limestone) removes the basic impurities. Carbon is oxidised to carbon monoxide by carbon dioxide. Carbon monoxide oxidises ironi(Il) oxide to iron(ll) oxide. Molten iron floats on the molten slag. cy Which of the following uses is incorrect? A Cast iron for woks B_ Galvanised steel for cutlery © Stainless steel for hospital equipment D__ Steel for cans and containers co ‘Ametal, M, takes part in the reactions shown by the following chemical equations: 2M + 02—» 2MO M + 2HCI—» MCl, + Ho mo + c—He8t_, no reaction Which metal could M be? A tron B Lead © Magnesium D = Zinc ( ) Hydrogen was passed over 1.0 g of heated copper(ll) oxide. What is the colour and mass of the product obtained? Colour of product Mass of product A black more than 1.0 ¢ B black less than 1.0 ¢ © reddish-brown more than 1.0 g D reddish-brown less than 1.0 Ca © 2014 Marshal Cavendish Education Pte Lid worsen 30 TTSection Sehr Answer the following questions in the spaces provided. 4. Metals were added in excess to aqueous solutions of different metal nitrates. The table below records the observations obtained. A tick (V) indicates @ reaction. A cross (X) indicates no reaction. ee pacer ve fe Zine nitrate = = x x 7 x z 7 7 7 7 : 7 v x Silver x x x zing v w M. (a) Place the metals in order of the reactivity, starting with the most reactive metal. (b) Which metal and aqueous metal nitrate would react to give the following colour changes? (i) Blue to green: (il) Colourless to blue: (©) Apart from colour changes, state two other observations that would indicate that a chemical reaction has taken place. (a) What are the conditions that can cause iron to rust? (b) Explain why rusting is an example of oxidation, TB Worwsheet 10 {© 2014 Marshall Cavendish Education Pte Ltd(c) (i) Car bodies can be protected from rusting by painting and sacrificial protection. Explain how the two methods work (il) What will happen if the paint on a galvanised car body is scratched off? Explain your answer. 3. The following list shows some elements in order of reactivity. Most reactive > Least reactive potassium > magnesium > carbon > iron > tin > gold (a) Some reactions of the metals are summarised in the table below. Metal Reaction with water or steam | Reaction with dilute acids potassium | violent reaction with cold water explosive magnesium, violent reaction with steam fast iron) slow reaction with steam slow tin ‘slow reaction with steam slow gold no reaction with water or steam no reaction (i) From the table, deduce the position of hydrogen in the reactivity series. (ll) Based on your answer in (a)(i), deduce a general rule for the reactivity of metals with water and dilute acids. {b) Why does gold occur mostly as pure gold in the Earth's crust, while potassium only occurs as potassium compounds? © 2014 Marshal Cavendish Education Pte Ltd Worksheet 10(c) Based on the order of reactivity of the elements, state the method that is most likely used to extract the following metals from their compounds. (i) Magnesium from molten magnesium chloride: (il) Tin from tin(!v) oxide: 4. The table below gives the densities and melting points of substances used in the blast furnace, at normal atmospheric pressure. i]s; tina ponte] calelum carbonate 271 decomposes at 850°C alum oxide 3.35 72600 calelum sileate 2.50 1530 carbon 225 ‘4000 iron 7.80 1539 iron) oxide 5.24 1566 magnesium oxide 2.58 2900 The diagram below shows the temperatures in a blast furnace. waste gases Some elements, including those used in the blast furnace, are shown below in decreasing order of reactivity. Ca>Mg>Fe>C>H>Ti BO Worksheet 20 © 2014 Marshal Caventish Education Pe Ltd(a) (b) (co) @ (e) {© 2014 Marshall Cavendish Education Pte Ltd Name the substances that are fed into the furnace at A. This reaction takes place at the base of the furnace: {s) + On(g) > COAg) How is the carbon dioxide formed immediately reduced to carbon monoxide? Write the equation for the reduction of iron(II) oxide by carbon monoxide. (Why Is the temperature of the slag coming out of B much lower than 1530°C? (il) Use the data from the table to explain why slag floats on top of molten iron. (lil) Why is it useful for slag to float on top of the molten iron? (i) The furnace is lined with magnesium oxide bricks. Suggest one physical property and ‘one chemical property of magnesium oxide that make it a suitable material. Physical property: Chemical property: (il) Why might the furnace explode if damp substances were added at A?eT Section C: Grea ee Answer the following questions. 1, Aluminium is the most abundant metal in the Earth’s crust. It has a low density and is corrosion- resistant. |n a laboratory, some experiments involving aluminium were set up. auriniam ‘luminium sniniam aluminium sto sip stp stip rubbed with rubbed with a oe ‘sandpaper sandpaper Iron calcium aqueous aqueous a in ion nitrate ‘aletm nitate Experiment 4 Experiment 2 Experiment 3 Experiment 4 Changes were only observed in Experiment 3, ¢ (a) Describe the observations you would see in Experiment 3. Write a balanced chemical equation for this reaction. (b) Suggest why a reaction occurred in Experiment 3 but not in Experiment 1. (¢) Based on the experimental results, arrange aluminium, calcium and iron in increasing order of reactivity. (d)_ The carbonates of calcium and iron decompose on heating. Based on your answer in (¢), deduce the thermal stability of aluminium carbonate. Explain your answer. 82 Worksneot 10 ‘© 2014 Marshall Cavendish Education Pte Lid2. Steel is an alloy of iron with carbon and/or other metals. It is made from cast iron extracted from the blast furnace. Steel has many uses and properties, (a) With the aid of diagrams, explain the difference between steel and iron in terms of structure. Structure of stee! Structure of iron (b) Explain how the difference in structures in (a) accounts for the difference in physical properties of steel and iron. (c) Carbon steel is a main category of steel. There are two types of carbon steel — high-carbon steel and mild steel, State how the compositions of high-carbon steel and mild steel account for their properties and uses. (d) Recycling metals helps to conserve natural resources and has many advantages. Discuss some problems faced in metal recycling. {© 2014 Marshall Cavendish Education Pte Lid venmeneWORK ON IT! Circle the question(s) that you have answered incorrectly. Then, revisit the relevant section(s) In the ‘textbook to strengthen your understanding of the key concept(s). ‘Question number(s) Textbook Leming outoomes a ae] ath choice nnn: response ‘wren (e)_Explan what an ay 1 - - 144 (0) ently the dlagrars of suuclures of metals and alloys. : al 2a) aa {Elin the aiference m the proportes o : alloys and their constituent metals. 7 bal 2(b) 14.4 (@) Determine the order of reactity of some ira fomths eactorscf mals | 7 i) - 142 Wattle ond cute ycrochers {@) Relate the reatviyof metas to reir {andonoy to form ste tne by othe Slacoment of metals Rom thee the placement of 4 - | a@ae | 14s + the vento of etl vith the oxide of another meta {Determine he order of veacty of Imetas om to egucton af metal oxides | 7, 8 . - 143 Wheaton and Pycogen (Deserve te action of heaton mata Catone aor tew mentee! | - 16) 143 Stat elated ote veel) series {hDoduce the over of eatvyof metals Wengen aso of exporimertarrests, | ~ 13 | ae | 148 {Reet the method of obtaining te metal from its ore to its position in the reactivity - 3(b), 3(c) - 14.4 Describe and expan te reactors Ioted inthe oxranton often the 5 4 144 Bist frnce {W_ldenity and dosotbe sea 9s on soy - - 20) 1s {Desc now the properties of tel vary with the amount of carbon or other metals. - - 2(c) 14.5 Sed fore (i) State the uses of Hoel é e 2) was (0) Describe te condtons necessary for rusting to occur. ~ (a) ~ 14.6 (0) Stee how rusting can be povered = 26) : 146 (6) Sst whyteeisaneedto eaete metas | 3 z : 147 {@) Discuss the osves related to escing metals. - - 2d) 147 {@_Detne oxidation asthe dah af onan. z 2) = wa (9) Detneoldaton as an ineease In [CO oksahn See” : 20) : 134 84 — Worksheet 10 (© 2014 Marshall cavendeh Education Pte Utd