Elements are classified broadly into two categories on the basis of properties: Metals:- Iron ,copper, zinc, aluminum etc. Non-metals:- Oxygen, nitrogen, hydrogen, chlorine, sulphur etc. Apart from metals and non-metals some elements show properties of both metals and non-metals, e.g. Arsenic, silicon, germanium. They are called metalloids.
(i) Action of air:-most of the metals react with air at high temp to form their basic oxides.
2Cu + O2 → 2CuO copper(II)oxide (black)
some oxides are amphoteric in nature. For example Al2O3.
Amphoteric oxides: - Oxides which react with both acids and bases to give salt and water.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Al2O3 + 2NaOH → 2NaAlO2 + H2O
Sodium aluminate Metal oxides those are soluble in water are called alkalies. For example Na2O & K2O. Na2O + H2O → 2NaOH K2O + H2O → 2KOH
(i) Na & K are most reactive metals. They react with air so vigorously that they catch fire when kept in open. So they are stored in kerosene.
(ii) Metals like Al, Zn, Pb, Sn do not react with air at room temp due to formation of oxide layer on their surface.
(iii) Silver and gold do not react with oxygen even at high temp.
(ii) Action of water
Metal + Water → Metal oxide + Hydrogen Metal oxide + Water → Metal Hydroxide.
Metal like Na, K catch fire when treated with cold water. This is due to the large amount of heat produced during the reaction. The hydrogen gas evolved during the process catches fire due to heat. Metals like Mg, Fe, Zn react only with steam to give corresponding oxide and H2 gas.
(iii)Action of acids
Metal + dil. Acid → Salt + H2 gas.
Note:- only Mn & Mg give H2 gas when treated with dil HNO3.
(iv) Action of metals with aqueous solution of other metal salts:-
metal A + salt solution of metal B → salt solution of A + metal B
Note:- The displacement take place only if metal A is more reactive than metal B.
Reactivity series:- On the basis of the relative reactivities, metals are arranged in order of decreasing reactivities.
Ionic Compounds Compounds formed by metal and non-metal are generally by transfer of electrons such compounds which are formed by formation of ions are called ionic compounds
Na -----àNa+ + e- 2,8,1 2,8 (sodium cation)
Cl + e- --------àCl- 2,8,7 2,8,8 (chloride anion)
Na + Cl ----à(Na+) [ Cl ]-
Properties of ionic compounds:-
· Ionic compounds are hard
· They have high melting and boiling points
· They are soluble in water
· They conduct electricity in aqueous and molten state
Occurrence and extraction of metals:-
Minerals:-The compounds of an element that occurs naturally in the earth’s crust.
Ores: - The minerals from which an element can be profitably and conveniently extracted. Enrichment of ores: - It is done to remove earthy impurities like clay, sand etc. from an ore is called enrichment or concentration of the ore.
Gangue: - The earthy impurities that is found with ores.
Extracting metal low in activity series:-
The metals low in the reactive series are very less reactive. The oxides of such metals can be reduced to metals by heating alone e.g.
2HgS(s) + 3O2 heat------à 2HgO(s) + 2SO2(g)
2HgO(s)-------à 2Hg(l) + O2(g)
Extracting Metals in the Middle of the Activity series
Metals like iron, zinc, lead etc. occur as sulphides or carbonates in nature. First the ore is converted into its oxide form This is done by either roasting or by calcinations
Roasting:- 2Zns(s) + 3O2 (g) heat 2ZnO +2SO2 (g)
ZnCO3(s) heat ZnO(s) +CO2(g)
SMELTING The metal oxide is reduced to metal by using suitable reducing agent such as Carbon. Extracting metals towards the top of activity series:- The metals high up in the activity series are very reactive. They cannot obtain by reduction of their oxides by carbon. These metals are obtained by the electrolysis of their molten chlorides e.g. Extraction of Na from NaCl
At cathode Na+ + e- àNa
At anode 2Cl- ------à Cl2 + 2e-
Refining of metals: - Most important method of refining of metals is electrolytic refining.
In this method the impure metal is taken as anode and pure metals is taken as cathode and the electrolyte used is aq. Salt solution of the metals Corrosion Active metals get oxidized by air and moisture For e.g. Rusting of iron:-due to formation of hydrated ferric oxide
Fe2O3+xH2O--------à Fe2O3.xH2O Rust.
Blackening of silver: - due to formation of silver sulphide.
Formation of green layer on items made of copper:-due to formation of basic copper carbonate :- CuO+H2O+CO2 -------à Cu(OH)2,CuCO3(Green)
· Prevention of corrosion Galvanizing
Metal and non-metals
1 marks questions (very short answer type question)
Q.1:- Name a metal which can be cut with a knife?
Q.2:- hich metal is the best conductor of electricity?
Q.3 Which metal is poorest conductor of electricity?
Ans:- iron Q.4 Which metal is most ductile?
q.5 Which metal is best conductor of heat ?
ans:- silver(and copper)
Q.6:- Which metal other than mercury is liquid at room temperature? Ans:- Gallium
Q.7:- Which metal is poorest conductor of heat?
Ans:- lead (and mercury)
Q.8:- What is the nature of oxides of metal?
Q.9:- What is the nature of oxides of non- metal?
Q10:-Which non-metal conduct electricity?
Ans:-Graphite, allotrope of carbon conduct electricity.
Q.11:- Which non-metal is lusturous? Ans:- iodine
Q.12:- Why metals are hard and have high melting point?
Ans:- because of their crystalline structure metals are hard.
Q.13:- What is an amalgam? Ans:- An alloy of two metals in which one is mercury is called amalgam.
Q.14:- What are the constituents of solder?
Ans:- tin and lead
Q.15:- Name the green coloured compound which appears on the surface of copper utensils?
Ans:- Basic copper carbonate
q.16:- Why the item made of silver turns black when exposed to air?
Ans:- due to formation of silver sulphide
2 marks questions (short answer type question)
Q.1:- What are amphoteric oxides? Give an example.
Ans:- Oxides which react with both acids as well as bases to produce salt and water are called amphoteric oxides .for example:- Al2O3 . ZnO
Q.2:- Name two metals that react with dil.HNO3 to evolve H2 gas ?
Ans:- magnesium and manganese Q.3:- Why metals like potassium and sodium catch fire when treated with water? Ans:- The reaction between sodium and water is so violent that the H2 gas released catches fire .
Reaction:- 2Na(s) + 2H2O(l) ----------à2NaOH(aq) + H2(s) + heat energy
Q.4:- Why sodium is kept immersed in kerosene oil?
Ans:- because sodium react with air to form Na2O (sodium oxide).
Q.5:- Which gas is produced when dil. HCl is added to a reactive metal? Write the chemical reaction when iron reacts with dil. H2SO4?
Ans:- hydrogen gas is produce when dil. HCl is added to a reactive metal.
Fe(s) + H2SO4(dil.) ------àFeSO4(aq) +H2(g)
Q.6:- What would you observe when zinc is added to a solution of iron(II) sulphate ?write the chemical reaction that takes place.
Ans:- The solution of iron(II)sulphate slowly turns to colourless and grey coloured layer of Fe is deposited on the surface of zinc metal.
Zn(s) + FeSO4(aq) -------àZnSO4(aq) + Fe(s)
Q. 8:- Why ionic compounds have high melting points?
Ans:- Ionic solids have crystalline structure in which there is strong interionic attraction. So large amount of energy is needed to overcome this force of attraction.
Q. 9:- What do you mean by roasting? How it is different from calcination? In which types of ores roasting is done?
Ans:- Heating an ore strongly in excess of air is called roasting. This is done to convert sulphide ores into its oxide form. Calcination is different from roasting because it is done in absence of air.
2ZnS(s) + 3O2(g) heat -------à2ZnO(s) + 2SO2
Q10:- Define :- (i) Ore, (ii) Mineral.
Ans:- Ore:- The minerals from which an element can be extracted profitably and conveniently is called ore. E.g. - Bauxite, Al2O3.2H2O – is an ore of aluminum.
Mineral:- The compounds of elements that occurs naturally in earth‘s crust are called minerals. E.g.- Glauber‘s salt Na2SO4.7H2O; Borax Na2B4O7.10H20 are two mineral sources of Sodium.
Q.11:- Name two metals which are found in nature in the free state.
Ans:- Silver and Gold.
Q.12:- Define :- (i) Enrichment of Ores (ii) Gangue. Ans:- (i) Removal of earthly impurities like sand, clay from an ore is called enrichment of ore.
(ii) The earthy impurities like sand, clay that are found along with an ore are called gangue or matrix. Q.13:- Write short notes on electrolytic refining of metals.
Ans:- In electrolytic refining the impure metal is taken as anode and the pure metal is taken as cathode. These two rods are dipped in aqueous salt solution of the same metal and electricity is passed. Pure metal from anode is dissolved into the solution and equivalent amount of pure metal from the electrolyte is deposited at the cathode
Q.14:- Name the conditions which are essential for corrosion.
Ans:- (i) Presence of moisture, (ii) Presence of air.
Q.15:- What is Galvanisation? Write its use.
Ans:- Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of Zinc.
Short Answer Type Questions:- (3 marks)
Q.1:- Write suitable example, explain how a metal low in the activity series can be extracted?
Ans:- Metals low in the activity series are less reactive. The oxides of these metals can be reduced to metals by heating alone. For example, extraction of Mercury (Hg) from Cinnabar (HgO).
2HgS(s) + 3O2(g) heat-----------à 2HgO(s) + 2SO2(g)
2HgO(s) heat -----------------à2Hg(l) + O2(g)
Q.2:- Write three properties of ionic compounds.
Ans:- (i) Ionic compounds have high melting points. (ii) Ionic compounds are soluble in water. (iii) Ionic compounds conduct electricity in aqueous and molten state.
1. What is anodizing? What is its use?
Ans. The process of forming a thick oxide layer of aluminium oxide that makes it resistant to further corrosion.
2. What is aqua regia? What is its use?
Ans. Aqua regia is a mixture of conc. HCl and conc. HNO3 in the ratio 3:1. It can dissolve gold and platinum.
3. What do you mean by thermite reaction? What is its use?
Ans. The reaction between Iron(II) oxide Fe2O3 with Al is used to join rail track joints or cracked machine parts. This reaction is known as thermit reaction.
Fe2O3 (s) + 2Al (s) 2Fe (l) + Al2O3 (s) + Heat
4. Why active metals do not liberate H2 gas when treated with dil. HNO3?
Ans. This is because HNO3 is strong oxidizing agent. It oxidizes H2 produced to water and itself gets reduced to nitrogen oxides.
5. Sometimes the ore itself acts as a reducing agent. Give an example.
Ans. During roasting of Cu2S, the ore itself acts as a reducing agent.
2CuS (s) + 3O2(g) → 2Cu2O(s) + 2SO2(g)
2Cu2O + Cu2S → 6Cu(s) + SO2(g)
MCQ for practical skills
1. An iron nail is dipped in copper sulphate solution. It is observed that
I. The colour 0f the solution remain unchanged .
II. The colour 0f the solution becomes red .
III. The colour 0f the solution turns to light green .
IV. None of these
I. turns dry blue litmus paper red
II. turns moist blue litmus paper red
III. turns moist red litmus paper blue
IV. none of these
3. Metal A when dipped in solution of salt of metal B ,then metal B is displaced . this shows that
I. Metal A is more reactive than metal B
II. Metal B is more reactive than metal A
III. Metal A and metal B are equally reactive
IV. None of these
4. When iron nail is dipped in aqueous solution of copper sulphate , it is observed that
I. Brown coloured layer is formed on the surface of iron nail
II. Blue coloured layer is formed on the surface of iron nail
III. green coloured layer is formed on the surface of iron nail
IV. none of these
MULTIPLE CHOICE QUESTIONS
Q.1-which of of the following metals will not react with oxygen,even when heated very strongly in air? (a) Zn (b) Al (c)Ag (d)Fe
Q.2-electrometallurgical process is employed to extract?
(a)Fe (b)Pb (c)Na (d)Ag
Ans – © Na
Q.3-which of the following elements occurs in free in nature
(a)Co (b)Fe (c)Ni (d)Pt
Ans-(d) Pt Q.4-What is not true about calcinations?
(a)to remove all organic matter (b)to convert ore into metal
©to remove moisture from the ore (d)to decompose carbonates and hydroxides
Ans-(b)to convert ore into metal.
Q.5 what is not true about roasting?
(a)to convert sulphides into oxides
(b)to remove volatile impurities ©to dry the ore
(d)to convert the the ore into fine powder
Ans-(d) to convert ore into fine powder
Q.6 which of the following pairs will give displacement reaction
(a)NaCl solution and copper metal (b)MgCl2 solution and aluminium metal
©FeSO4 solution and silver metal
(d)AgNO3 solution and copper metal
Ans-(d) AgNO3 solution and copper metal
Q.7-A non-metallic oxide which is neutral in nature is
(a)CO2 (b)CO ©P2O5 (d)none of these