CBSE Class 10 Science Metals And Non Metals Notes Set 03

METALS & NON-METALS

Comparison of properties of metals & non-metals

Anodizing: Process of forming a thick oxide layer on the surface of metal. For eg., \( Al \) article is made anode. Cathode is made from any inert electrode like graphite. \( H_2SO_4 \) is taken as electrolyte. \( O_2 \) gas evolved at anode reacts with \( Al \) on the surface of \( Al \) article to make a thick protective oxide layer. This oxide layer can be dyed easily.

Reaction of metals with water

• The order of reactivity of metals with dil. \( HCl \) is \( Mg > Al > Zn > Fe > Cu \).
• Metals on reaction with \( HNO_3 \) do not produce \( H_2 \) as \( HNO_3 \) is a strong oxidizing agent and oxidizes \( H_2 \) to \( H_2O \) and itself gets reduced to oxides of nitrogen.
• \( Cu \) reacts with hot & conc. \( H_2SO_4 \) to produce \( CuSO_4, SO_2, \) & \( H_2O \).
• Magnesium and manganese are two metals which react with very dilute \( HNO_3 \) to evolve hydrogen gas.
• \( Fe \) reacts with dil. \( H_2SO_4 \) to evolve \( H_2 \) gas.
• Aqua regia is a freshly prepared mixture of conc. \( HCl \) and conc. \( HNO_3 \) in the ratio \( 3 : 1 \). It can dissolve gold, even though neither of these acids can do so alone. It is a highly corrosive, fuming liquid. It is one of the few reagent that is able to dissolve gold and platinum.

Reaction of metal with solutions of other metal salts

A more reactive metal displaces a less reactive metal from its aqueous salt solution. This is known as displacement reaction. It is many-a-times observed by a colour change in the salt solution or deposition of the displaced metal.

\( CuSO_4(aq) + Fe(s) \to FeSO_4(aq) + Cu(s) \)
(Blue)                           (Green)      (Brown)

A brownish deposition of copper is observed on the surface of iron nail dipped in a blue coloured copper sulphate solution, which turns green due to the formation of ferrous sulphate on account of higher reactivity of iron.

Activity series of some metals

• Potassium (K) - Most Reactive
• Barium (Ba)
• Calcium (Ca)
• Sodium (Na)
• Magnesium (Mg)
• Aluminium (Al)
• Zinc (Zn)
• Iron (Fe)
• Nickel (Ni)
• Tin (Sn)
• Lead (Pb)
• Hydrogen (H)
• Copper (Cu)
• Mercury (Hg)
• Silver (Ag)
• Gold (Au) - Least Reactive

Reaction of metals with non-metals

• Metals are electron donors therefore, they becomes a cation to achieve nearest noble gas configuration and become stable.
• Non-metals are electron acceptors therefore, they become anions to achieve nearest noble gas configuration and become stable.
• When a metal donates an electron and non-metal accepts the same electron, they get bound by strong electrostatic forces of attraction and form ionic bond or electrovalent bond. This can be represented by lewis dot structure.
• \( Na + \cdot \ddot{Cl} : \to [Na]^+ [\cdot \ddot{Cl} :]^- \)
• The combining capacity of an element is called its valency.
• Element losing an electron gains a positive charge while an element gaining an electron gets a negative charge on it.

Properties of Ionic compounds

• Physical state: They are solid, relatively hard, held together by strong electrostatic force of attraction and are generally brittle.
• Solubility: As ionic compounds are polar in nature, so they dissolve in polar solvent like water and are insoluble in non-polar solvents like kerosene.
• Melting & Boiling Points: As they are bound by strong electrostatic forces of attraction. So, a large amount of energy is needed to break these bonds.
• Conduction of electricity: Ions do not move in solid state so ionic compounds conduct electricity in molten or aqueous solution only.
• Colour to the flame: Most metal salts when brought into the flame, impart characterisic colour to the flame.

Occurrence of metals

• Metals occur either in their native state or combined state (depending upon their reactivities).
• Elements in reactivity series from K to Al are highly reactive and Zn to Pb are moderately reactive, so are always found in combined state. Elements from Cu to Ag are less reactive, so can be found in free as well as combined state. Elements from Pt to Au are least reactive so are found in free state.
• The elementary state of compounds in the form of which metals occur in nature are called minerals.
• The minerals from which metals can be conveniently and profitably extracted are called ores.
• Therefore, all ores are minerals but all minerals are not ores.
• The process of extracting metal from its ore, followed by refining of metal is known as metallurgy.
• Crushing of ore is done in hammer-mill or jaw-crusher.
• Grinding is done in ball mill or stamp mill. Crushing & grinding together are known as pulverisation of ore.
• Impurities in ore, are called as gangue or matrix. Removal of impurities is known as enrichment of ore.
• Various separation techniques are employed based on the properties of ores and gangue:
  • Levigation is based on difference in densities. Eg. Haemetite ore of iron.
  • Froth floatation is based on difference in wetting properties of the ore and gangue particles. e.g. ZnS.
  • Liquation is based on difference in melting points of ore and gangue particles. e.g. ore of tin & Zn.
  • Magnetic separation is based on magnetic properties of ore and gangue. e.g. Magnetite ore of iron (\( Fe_3O_4 \)).
  • Leaching is used when none of the physical properties work, then chemically ore and gangue is separated. e.g. Bayer’s process for alumina enrichment.

Extraction of metals from the enriched ore

• Metals lying low in activity series (Cu, Hg, Ag, Pt, Au)
  • Found in native state or in the form of sulphides.
  • Sulphide ore \( \xrightarrow{\text{Heating in excess of air}} \) Roasting \( \to \) Oxide \( \xrightarrow{\Delta} \) Metal \( \to \) Refining.
  • Eg. \( HgS \xrightarrow{O_2} HgO \xrightarrow{\Delta} Hg \).
  • The reaction in which one of the reactant (\( Cu_2S \)) carries the reduction of the product (\( Cu_2O \)) is known as auto reduction or self reduction.
• Metals lying in middle of activity series (Fe, Zn, Pb, Sn, Ni, Mn, Cr, etc.)
  • Found as carbonates or sulphides.
  • Carbonates \( \xrightarrow{\text{heating in limited air}} \) Calcination \( \to \) Oxide (ZnO).
  • Sulphide (ZnS) \( \xrightarrow{\text{Roasting}} \) Oxide (ZnO).
  • Reduction of oxide:
    • Reduction by carbon/coke.
    • With CO.
    • With Aluminium (Thermite reaction). Reaction is highly exothermic, Metal obtained is in molten state.
  • Metal \( \to \) Refining.
  • Reduction by carbon is also known as smelting.
• Metals lying in high up in activity series (K, Ca, Na, Mg & Al)
  • Found as oxides or halides.
  • Have strong affinity for oxygen so cannot be reduced by carbon. Hence, electrolytic reduction is employed.
  • Electrolytic Reduction: Eg. NaCl (molten or aqueous)
    \( NaCl \xrightarrow{\Delta} Na^+ + Cl^- \)
    Cathode - Reduction of Metal ion: \( Na^+ + e^- \to Na(s) \). Metal obtained at cathode.
    Anode - oxidation of non metal ion: \( Cl^- \to Cl(g) + e^- \), \( Cl + Cl \to Cl_2(g) \).

Refining of impure metal

Extraction of metal is followed by electrolytic refining process. e.g. Electrolytic refining of copper (impure).

• On passing electric current through electrolyte, the pure metal from the anode dissolves into the electrolyte.
• An equivalent amount of pure metal from the electrolyte gets deposited on the cathode.
• The soluble impurities go into the solution, leaving the insoluble impurities which settle down at the bottom of the anode as anode mud.

At Anode: \( M(s) \to M^{n+}(aq) + ne^- \) (Metal atom from anode to Metal ion)
At Cathode: \( M^{n+}(aq) + ne^- \to M(s) \) (Metal ion from solution to Metal atom)

Corrosion

• The process of slowly eating up of metal due to their conversion into oxides, carbonates, sulphide, sulphate, etc. by the action of atmospheric gases and moisture is called corrosion.
• In case of iron it is called rusting.
• Factors affecting corrosion: Position in activity series, presence of water vapour & gases like \( CO_2, SO_2 \), etc., and presence of salt or electrolyte in water.
• Prevention: Painting, self prevention (forming protective layer on its surface), cathodic protection (setting up of electrochemical cell by connecting to a less reactive metal and preventing oxidation), oiling and greasing. Electroplating (galvanization/ tinning) and by alloying.

Alloys

An alloy is a homogeneous mixture of two or more metals or non-metal. It can be prepared by first melting the metal and then dissolving the other elements (metal or non-metal) in proper proportions. The physical properties of an alloy are different from the constituent metals (from which it is made).

Alloy has the following characteristics properties:

(i) Alloys are stronger than the metals from which they are made.

(ii) They are harder than constituent metals.

(iii) They are more resistant to corrosion.

(iv) They have lower melting points than the constituent metals.

(v) They have lower electrical conductivity than pure metals.

Some of the common alloys are

(i) Duralumin: It is an alloy of aluminium. It contains 95% of aluminium, 4% of copper, magnesium is 0.5% and 0.5% of manganese. It is stronger and lighter than aluminium. Duralumin is used for making bodies of air crafts, helicopters, jets, kitchen ware like pressure cooker. It is also used for making bodies of ships (due to its resistance to sea water corrosion). It is also known as duralium.

(ii) Amalgam: It is an alloy of mercury and one or more other metals is known as an amalgam. It may be solid or liquid. A solution of sodium metal in liquid mercury metal is called sodium amalgam, which is used as a reducing agent. Amalgam of silver, tin and zinc is used by dentists for filling in teeth.

(iii) Alloys of Gold: The purity of gold is expressed is terms of 'carats'. Pure gold is known as 24 carats gold. It is very soft due to which, it is not suitable for making jewellery. It is alloyed with either silver or copper to make it hard and more suitable for making ornaments. In India, gold ornaments are usually made of 22 carats gold. It is an alloy of gold with silver or copper. Twenty-four-karat gold is an element. It contains only gold atoms. Fourteen-karat and 18-karat gold are alloys. They contain a mixture of different atoms.

Alloys of copper

Alloys of zinc