Metals

Objectives By the end of this lesson, you should be able to:  1. describe the general physical properties of metals  2. describe an alloy and give examples of alloys  3. identify representations of metals and alloys from diagrams of structures  4. explain why alloys have different physical properties to their constituent elements  5. construct equations, with state symbols, for the reaction of metals with water, steam and HCl

Physical Properties  Ductile- can be stretched to form wires  Malleable- can be bent and beaten into different shapes  Good conductors of heat and electricity  Shiny  High melting and boiling points  High density  Strength  Sonorous

Alloys  Alloys are mixture of two or more metallic elements or mixture of metallic and non-metallic elements.  Pure metals are soft as its layers of atoms can slide over one another, whereas in an alloy, the atoms has different sizes, so this disrupts the orderly layers of atoms and make it more difficult for the layers to slide over each other.  Alloys are harder and stronger than pure metals.

Fig.1 Simplified diagram of metal structure Fig. 2 Simplified diagram of structure of an alloy

Some Alloys and their uses AlloyMain ComponentsSome usesUseful properties DuraluminAl, Cu, MgAero planesLight & strong BrassCu, ZnDoorknobs, ornaments Corrosion resistant & hard BronzeCu, SnShips’ propellers, bells, statues Corrosion resistant & hard Cupro-nickelCu, Ni‘Silver’ coinsCorrosion resistant, looks like silver Titanium alloyTi, Fe, CAero planesLight & strong, low expansion when heated SolderPb, ZnJoining wiresVery low melting point ( 170 degree)

Some alloy steels TypeTypical CompositionTypical uses Chromium steelUp to 5% CrBall bearings Cobalt steelUp to 10% CoMagnets Molybdenum steelUp to 4% MoGun barrels Stainless steelOften 18% Cr, 8% NiSinks, cutlery Tungsten steelUp to 18% WTools, armour plate Vanadium steelUp to 2% VSpanners, tools

Reactions of group 1 metals with water

Reaction of Metal with Water  Potassium- reacts very vigorously with cold water, KOH and hydrogen gas is produced, lot of heat is produced causing hydrogen to catch fire & explode. 2K(s) + 2H 2 O(l) → 2KOH(aq) + H 2 (g)  Sodium- reacts vigorously with cold water, hydrogen gas produced, may catch fire & explode. 2Na(s) + 2H 2 O(l) → 2NaOH(aq) + H 2 (g)  Calcium- reacts readily with cold water, many bubbles of hydrogen gas is produced. 2Ca(s) + 2H 2 O(l) → 2Ca(OH) 2 (aq) + H 2 (g)

 Magnesium- reacts very slowly with cold water, few bubbles of hydrogen gas produced, but, hot magnesium reacts vigorously with steam, produce MgO & hydrogen gas. Mg(s) + H 2 O(g) → MgO(s) + H 2 (g)  Zinc- does not react with cold water, hot zinc reacts with steam Zn(s) + H 2 O(g) → ZnO(s) + H 2 (g)  Iron- does not react with cold water, hot iron reacts slowly with steam, produce iron(II, III) oxide (black iron oxide) and hydrogen gas. 3Fe(s) + 4H 2 O(g) → Fe 3 O 4 (s) + 4H 2 (g)  Lead, Copper & Gold- have no reaction with water or steam.

Reaction with dilute HCl  Potassium- explodes, KCl and H 2 gas produced. 2K(s) + 2HCl (aq) → 2KCl (aq) + H 2 (g)  Sodium- explodes, NaCl & Hydrogen gas produced. 2Na(s) + 2HCl (aq) → 2NaCl (aq) + H 2 (g)  Calcium- reacts very fast, many bubbles of hydrogen gas, Calcium chloride obtained. Ca(s) + 2HCl (aq) → CaCl 2 (aq) + H 2 (g)  Magnesium- reacts fast, many bubbles of hydrogen gas Mg(s) + 2HCl (aq) → MgCl 2 (aq) + H 2 (g)

 Zinc- reacts moderately fast, many bubbles of hydrogen gas. Zn(s) + 2HCl (aq) → ZnCl 2 (aq) + H 2 (g)  Iron- reacts slowly, bubbles of hydrogen gas, a pale green solution of iron (II) chloride obtained. Fe(s) + 2HCl (aq) → FeCl 2 (aq) + H 2 (g)  Lead- reacts very slowly with warm HCl.  Copper & Gold- have no reaction

Self-Test  1. What 2 physical properties of copper make it useful for use as circuit wires? (2 marks)  2. The 10- cent coin consists of 75% copper and 25% nickel. (a) What is the name used for mixtures of metals? (1 mark) (b) Sketch a diagram to show how the atoms are arranged in the coin. (1 marks)  3. Construct equations, with state symbols, for the following reactions. (a) The metal barium reacts with cold water to form a solution of barium hydroxide, Ba(OH) 2 (2 marks) (b) The metal aluminium reacts with warm hydrochloric acid to form a solution of aluminium chloride, AlCl 3 (2 marks)  4. Describe the word “ductile” and “malleable”(2 marks)