Metals

Alumina is the oxide of aluminium (aluminium oxide), which is produced from refining of bauxite.

Roasting is the process in which sulphide(S^-2) containing ore is heated in the presence of excess of air (O₂) for a long time and it is converted into oxide.

So, in this question only in option (B) zinc sulphide (ZnS) reacts with the excess of oxygen to form zinc oxide (ZnO).

Alloy is a homogeneous mixture of 2 or more metals or metal and non-metal. In this question we will get the solution by options.

•In option (A) silver is a metal not a mixture and option

•(B) gallium is also metal and option

•(D) 24 carat gold is the pure form of gold but option

•(C) 22 carat gold is an alloy which consists of 22 parts of gold and 2 parts of other metals such as copper or silver. So, the correct option is (C).

Let us take all the options from start.

•In option (A) if metal reacts with sulphuric acid salt of corresponding acid and dihydrogen gas is formed and same thing happens for option (B) also.

•When metal reacts with nitric acid it does not produce dihydrogen gas instead of that oxide of nitrogen is formed because nitric acid is strong oxidising agent.

•So, the correct option is (C).

•In option (D) when metal reacts with water metal hydroxide or metal oxide and dihydrogen gas is formed.

According to the activity series copper is more active than silver so the displacement reaction in the (C) option. In other options the solution metal is more active so no displacement reaction can take place.

In the first three options the metals were more active than the solution so they could displace them but Cu is less active than Fe so it can’t displace it. So, the correct option is (D).

Reduction is the method in which pure metal is obtained from the metal oxide.

If we check option by option then we can clearly see that in option (B) it is mentioned that metals have low melting and boiling points but it is not true generally metals have high melting and boiling point. So, option (B) is correct.

Melting point of alloy prepared from lead and tin is low so it is used to solder electric wires.

Aluminium is the most abundant metal available on earth. It makes up to 8% of Earth’s crust by weight.

Mercury is liquid at room temperature and it is also sensitive to temperature so it is used in thermometer.

Hygroscopic is a substance which absorbs moisture from air. Anhydrous calcium chloride is highly hygroscopic that is the reason it is kept in tightly sealed container.

All the elements are classified into 3 sections they are:

Metals, Non-metals and semi metals (metalloids).

Metals: A metal is a material that is hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable and ductile.

Non-metals: Non-metals have low melting and boiling points, densities, brittle if solid, and are usually poor conductors of heat and electricity.

Metalloids: A metalloid is an element that exhibits some properties of metals and some of non-metals.

Gold and platinum ate the metals available in free state because of their very low activity.

If in a certain mineral metal proportion is more and its extraction is advantageous then it is called ore. Ores are found in combined form in nature such as silicate, carbonate, oxide, phosphate, sulphide, etc.

The main 2 ores of iron are Haematite its formula is Fe₂O₃ and Magnetite its formula is Fe₃O₄. These ores are mainly found in the region of Madhya Pradesh, Tamil Nadu, Orissa, etc.

The 2 ores of copper are Cuprite (Cu₂O) and Copper Glance (Cu₂S). These ores are mainly found in the region of Rajasthan and Bihar.

Three methods of concentration of ores are:

(i) Concentration or centrifugation on the basis of difference of densities: This method is used when there is large difference in densities of ores and impurities.

(ii) Froth floatation method: This method is used for the concentration of ores of the metals whose ores are in sulphide form.

(iii) Magnetic separation: This method is used when either of ore or the impurity have some magnetic properties.

Reduction is carried out to obtain metal from metal oxide.

The 2 methods used to reduce metal oxide are:

i) Chemical reduction: When metal oxide is heated in blast furnace with carbon or carbon monoxide, metal is obtained.

e.g.

ii) Electrochemical reduction: Oxides of active metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.

e.g. electrochemical reduction of alumina to obtain aluminium.

The method to obtain about 100% pure metal by removing impurities in very small amounts in metal is called refining.

The three methods used for refining of metals are:

i) Electrolysis: In this method the rod of impure metal is taken as anode and rod of pure metal as cathode. The aqueous solution of salt of metal acts as electrolyte, when current is passed anode dissolves in electrolyte and the same amount of metal is deposited on cathode.

ii) Liquefaction: In this method furnace having a slope is used and the temperature of the furnace is kept higher than the melting point of metal.

When the impure metal is passed on the slope, the metal in it get melted and collected in the vessel but the melting point of impurities is high so they remain on the slope in solid form.

iii) Zone refining: In this method we remove trace impurities which are generally more soluble in molten metal, their solubility decreases as the metal cools and impurities are separated in the form of crystals.

In the method of electrolysis the rod of impure metal is taken as anode and rod of pure metal is taken as cathode. The aqueous solution of salt of, metal is used as an electrolyte. On passing electric current the anode dissolves in the electrolyte and the same proportion of pure metal gets deposited on cathode.

Refining of copper by electrolysis

Bauxite is the ore of the aluminium by processing of bauxite aluminium is obtained from it. Some of the chief impurities present in the bauxite are iron oxide (Fe₂O₃) and silica (SiO₂).

To obtain the alumina from aluminium by electrochemical reduction in which alumina has high melting point to bring down its melting point feldspar (CaF₂) is added and cryolite (Na₃AlF₆) is added to increase the electrical conductivity so that electrolysis could be carried out easily.

It is the waste material separated from metals during smelting or refining of ore.

e.g. when Calcium silicate (CaSiO₃) formed as a result of the reaction of calcium oxide and silica in the blast furnace.

liquid cooled slag is used in construction of roads; it is used in concrete in combination with Portland cement.

The general principle that is taken into consideration in determination of activity series is “A less active metal can be displaced from the solution of its salt by a more active metal”.

In periodic table the elements present in group 1 i.e. alkali metals are soft and are easy to cut.

Two soft metals are:

Sodium (Na) and Potassium (K)

Metals are generally good conductors of electricity but there are 2 metals which are exception and they are:

Lead (Pb) and Mercury (Hg)

Generally metal oxides are basic in nature. So two metal oxides that are alkali by dissolving in water are:

i) Sodium oxide (Na₂O)

ii) Potassium oxide (K₂O)

Alkali metals burn with explosion in reaction with water and the 2 metals are:

i) Sodium

ii) Potassium

These metals react vigorously with water. The dihydrogen gas produced by these metals is so high that it explodes in water and burns speedily.

The metals which are generally inert in nature do not corrode. Two examples are:

i) Gold

ii) Platinum

Stainless steel is an alloy which is hard and strong and does not gets easily corroded. It is mainly mixture 3 metals they are:

i) Iron

ii) Nickel

iii) Chromium

Rust is a reddish coating when iron is attacked by moist air. The chemical formula of rust is Fe₂O₃.xH₂O.

i. 2PbS(s) + 30₂(g) _{2PbO(s) + SO2}(g)

_{PbO = Lead oxide}

_SO2 = Sulphur dioxide

ii. MgCO₃(s) MgO(s) + CO₂ (g)

MgO = Magnesium oxide

CO₂ = Carbon dioxide

iii. Fe₂O₃(s) + 3CO (g) 2Fe(s) + 3CO₂ (g)

Fe = Iron

CO₂ = Carbon dioxide

iv. Fe₂O₃(s) + 2Al(s) 2Fe(l) + Al₂O₃(s)

Fe = Iron

Al₂O₃ = Alumina

v. 2Al(OH)₃(s) Al₂O₃(s) + 3H₂O(g)

Al₂O₃ = Alumina

H₂O = Water

vi. CaO(s) + SiO₂(s) _CaSiO3 (l)

_CaSiO3 = Calcium silicate

vii. K₂O(s) + H₂O (l) _{2KOH (aq)}

_{2KOH = Potassium hydroxide}

_{vii. Mg(s) + 2H2}O (l) _Mg(OH)2(aq) + H₂ (g)

_Mg(OH)2 = Magnesium hydroxide

_H2 = Hydrogen

_{ix. Zn(s) + 2HCl (aq)ZnCl2} (aq) + H₂ (g)

_ZnCl2 = Zinc chloride

_H2 = Hydrogen

_{x. Ca(s) + Cl2} (g) _CaCl2(s)

_CaCl2 = Calcium chloride

To remove impurity from iron ore the method of magnetic separation is used. Powdered ore is allowed to fall on the belt.

A magnet at one end of the belt which attracts the iron particles and fall nearer, the remaining particles fall away because of not being attracted.

Thus, by method of magnetic separation impurity of iron is removed from the ore.

Copper pyrite (Cu₂S) is the ore of copper in the sulphide form so here method of froth-floatation should be used for concentration.

In this method, the fine powder of ore and water are filled in a big vessel and pine or turpentine oil is added to it. The sulphide particles of metals get wet and stick to it, while impurities do not get wet.

In this liquid mixture, air is passed with pressure through a tube. Hence, froth is produced around the light particles of the sulphide ore and comes to the surface of the liquid mixture.

The impurities get wet by water and settles down and the ore is removed with sieves and washed with water.

By this method clay, sand, etc are removed.

For refining of copper by electrolysis, impure copper rod is arranged as anode and rod of pure copper as cathode.

The aqueous solution of copper sulphate is taken as electrolyte.

When electric current is passed through the electrolyte the proportion of which copper from anode is dissolved in aqueous solution of copper sulphate and the same amount of copper from electrolyte is deposited on cathode.

Copper deposited on cathode is of 100% purity.

Four physical properties of the metals are:

i) The surface of metals is shiny and can be polished.

ii) Generally, metals are in solid form and heavy in weight but metals like mercury and gallium exist in liquid form.

iii) Metals are good conductors of heat and electricity except metals such as lead and mercury.

iv) Some of the metals are malleable and ductile. E.g. gold, etc.

Both brass and bronze are alloy.

Brass: The components of brass are Copper (Cu) and Zinc (Zn).

The uses of brass are in preparing cooking utensils, machinery parts and musical instruments.

Bronze: The components of bronze are Copper (Cu) and Tin (Sn).

The uses of bronze are in making statues, coins and medals.

Earth is a treasure of elements as different elements are obtained directly or indirectly from:

i) Lithosphere: It is the part of the earth formed of sand, clay and stone, in which metal elements like aluminium, copper, iron, calcium, sodium, zinc etc. are in the forms of oxide, sulphide or carbonate.

ii) Hydrosphere: It is the mostly liquid part of the earth water of seas, rivers, lakes and the ice of polar region. In this part of region non-metals such as chlorine, fluorine and metals like sodium, potassium, calcium, etc. are found in combined forms.

iii) Atmosphere: The cover of gases around the earth is called atmosphere. Non-metallic gases such as nitrogen, oxygen, carbon dioxide, etc. are present.

There are mainly three different methods for concentration of ores and they are:

i) Concentration or centrifugation on the basis of difference of densities: This method is used when there is large difference in densities of ores and impurities. In this method finely, powdered ore is placed on a moving table with slots and it is moved rapidly so that light particles of metal remain in the slot in the table

ii) Froth floatation method: This method is used for the concentration of ores of the metals whose ores are in sulphide form.

The fine powder of ore and water are filled in a big vessel and pine or turpentine oil is added to it. The sulphide particles of metals get wet and stick to it, while impurities do not get wet.

Air is passed with pressure through a tube and froth is produced around the light particles of the sulphide ore and comes to the surface of the liquid mixture.

The impurities get wet by water and settles down and the ore is removed with sieves and washed with water.

By this method clay, sand, etc are removed.

iii) Magnetic separation: This method is used when either of ore or the impurity have some magnetic properties.

Powdered ore is allowed to fall on a belt.

A magnet at one end of the belt which attracts the ore particles and fall nearer, the remaining particles fall away because of not being attracted.

Thus, by method of magnetic separation impurities are removed from the ore.

These are the methods which are used to convert ore into metal oxides.

i) Roasting: When sulphide containing ore is heated for a long time in presence of excess of air to form metal oxide, this method of converting sulphide containing ore into metal oxide in presence of excess of air is called roasting.

e.g.

ii) Calcination: When carbonate containing ore is heated for a long time in absence of air it is converted into metal oxide. This method of converting carbonate containing ore into metal oxide is called calcination.

e.g.

iii) Smelting: If the ore is in melted form then it is called smelting.

Reduction is the process in which metal oxides are converted into their respective metals.

There are 2 methods of reduction and they are:

i) Chemical reduction: This is the type of reduction in which metal oxide is heated with carbon or carbon monoxide to obtain the metal.

e.g. MnO₂(s) + 2C(s) → Mn(s) + 2CO(g)

Fe₂O₃(s) + 3CO (g) → 2Fe(s) + 3CO₂ (g)

Oxides of metals such as chromium, iron and manganese are heated with aluminium powder to obtain the metal.

e.g.

ii) Electrochemical reduction: All metals cannot be reduced by chemical method, some metals such as sodium, magnesium, etc cannot be reduced from carbon because of their more attraction towards oxygen. Hence, electrochemical reduction is used for the reduction of active metals.

In electrochemical reduction electrodes of inert metals like graphite or platinum are used in electrochemical cell.

e.g. electrochemical reduction of alumina to obtain aluminium.

Cathode: 2Al⁺³(l) +6e^-→ 2Al (l)

Anode: 3O^-2(l) → 3/2 O₂ (g) +6e^-

Some metals after reduction still contain some impurities which is further removed by refining. Two of which methods are:

iv) Liquefaction: This method is used for the metals having low melting point such as lead, tin, etc.

In this method furnace having a slope is used and the temperature of the furnace is kept higher than the melting point of metal.

When the impure metal is passed on the slope, the metal in it get melted and collected in the vessel but the melting point of impurities is high so they remain on the slope in solid form.

v) Zone refining: This method is based on the principle of fractional distillation to get a very high level of purity. Refining of semi metals is done by this method. In this method we remove trace impurities which are generally more soluble in molten metal, their solubility decreases as the metal cools and impurities are separated in the form of crystals.

Aluminium is the most abundant metal on Earth. It is extracted from bauxite (Al₂O₃.2H₂O) in 2 steps (i) to obtain alumina from bauxite (ii) to obtain alumina metal from alumina.

i) To obtain alumina from bauxite

Bauxite contains impurities such as iron oxide and sand (silica) is also present. Alumina is obtained from bauxite by Bayer’s process, in this process bauxite powder is taken and concentrated (45%) sodium hydroxide solution is added and then heated in closed vessel at 433 K temperature and 5 to 6 bar pressure, by hours by doing this aluminium oxide present in bauxite is converted into sodium aluminate which is soluble in water.

Al₂O₃(s) + 2NaOH (aq) → 2NaAlO₂ (aq) + H₂O (l)

Iron oxide is insoluble in water so it is removed by filtration but silica form sodium silicate which is soluble in water. Now, sodium aluminate and sodium silicate are there as filtrate. Excess of water is added and continuously stirred so that hydrolysis of sodium aluminate takes place and forms aluminium hydroxide and sodium silicate remains as impurity.

2NaAlO₂ + 2H₂O → Al(OH)₃ + NaOH

The precipitate is washed repeatedly with water, dried and on heating at 1473 K temperature pure aluminium oxide (alumina) is obtained.

ii) To obtain aluminium from alumina

To obtain aluminium from alumina is done by electrochemical reduction and also known as Hall-Heroult method. In this process cryolite (Na₃AlF₆) is added so that electrolysis could be done easily and this mixture also works as good electric conductor, further the melting point is also brought down by addition of feldspar(CaF₂).

The mixture of alumina, feldspar and cryolite is electrolysed in a vessel of iron having inner surface layered with carbon. In this the rods of carbon are joined by copper clamp which acts as anode and carbon layered graphite acts as cathode. When electric current is passed molten aluminium is deposited on cathode and dioxygen gas is produced at cathode. The molten aluminium is collected at the bottom of the cell is taken out.

Cathode: 2Al⁺³ + 6e^-→ 2Al

Anode: 3O^-2→ 3/2 O₂ 6e^-

The dioxygen gas produced at anode reacts with the rod of carbon and forms carbon dioxide, as a result anode gets corroded and should be frequently replaced.

Iron is extracted from haematite by reduction in blast furnace.

The blast furnace is narrow in upper part, wide in middle and narrow at bottom part. The inner side of blast furnace has brick which are fire proof.

Most of the impurities present in ore are removed and then the concentrated ore is added to blast furnace with the help of hooper.

Due to the high temperature following reactions takes place and molten iron is obtained.

i) Coke combines with oxygen and forms carbon dioxide, due to exothermic reaction the temp of furnace becomes 1773K to 1993 K.

C(s) + O₂(g) → CO₂(g) + Heat

ii) Calcium oxide and carbon dioxide are formed due to decomposition of lime stone due to high temperature.

CaCO₃(s) → CaO(s) + CO₂

iii) When hot carbon dioxide goes up in the furnace it combines with coke and forms carbon monoxide, due to the endothermic reaction temperature comes down.

CO₂ (s) + C(s) → CO(g)

iv) When the temp. of furnace is 673K to 973K, the iron oxide present in haematite is reduced to liquid form.

3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂

Fe₃O₄ + CO → 3FeO + CO₂

FeO + CO → Fe + CO₂

Calcium oxide formed during the reaction combines with impurity silica present in haematite and forms calcium silicate i.e. slag.

CaO + SiO₂→ CaSiO₃

Slag is lighter than iron so it floats and separated afterwards.

The activity series of metals is a list of metals ranked in order of decreasing reactivity to displace hydrogen gas from its aqueous solution. It can also be used to predict which metals will displace other metals in aqueous solutions.

Experiment:

Step-1: Take 2 test tubes and mark them as 1 and 2.

Step-2: In test tube 1 add 0.1 gram of copper sulphate and in test tube 2 add 0.1 gram of silver nitrate.

Step-3: Add 10 ml of water in both the test tubes and dissolve them.

Step-4: Now bring an iron nail and copper wire and add these to test tube 1 and 2.

Step-5: Place them in order and observe them.

Step-6: After 30 minutes we will observe that in test tube-1 iron nail will appear brown due to deposition of copper on it. In test tube -2 a white shining colour deposited on the copper wire.

Step-7: From the experiment we can conclude that iron (Fe) is more active metal than copper (Cu) because Cu from solution of CuSo₄ was displaced by iron i.e. Fe>Cu. Cu is more active metal than Ag because Ag was displaced from its solution of AgNO₃ by Cu metal i.e. Cu>Ag.

Thus the final order is Fe>Cu>Ag.

Activity series of metals:

K>Na>Ca>Mg>Al>Zn>Fe>Pb>[H]>Cu>Hg>Ag>Au

Chemical properties of metals are:

i) Reaction with dioxygen: Metal elements can easily donate electrons to dioxygen atom.

Metal elements combine with oxygen to form oxides.

Metal + Dioxygen → Metal oxides

e.g. 2Mg(s) + O₂(g) → 2MgO(s)

All metals do not react with dioxygen all metals show different properties such as metals like gold do not react with dioxygen at higher temperatures also.

ii) Reaction with water: Metals on reaction with water form hydroxides or oxides and produce dihydrogen gas. Metals such as sodium and potassium reacts vigorously with water and produce hydrogen gas.

Metal + Water → Metal hydroxide or Metal oxide + Dihydrogen gas

e.g. 2K(s) +2H₂O(l) → 2KOH(aq) + H₂(g)

Magnesium does not react with cold water but instead of it reacts with hot water to form magnesium hydroxide.

Mg(s) +2H₂O (l) → MgOH (aq) + H₂ (g)

Aluminium, zinc and iron metals do not reacts with hot or cold water but they react with water vapours to form oxides and hydrogen gas.

e.g. 2Al(s) +3H₂O (l) → Al₂O₃ (aq) + 3H₂ (g)

iii) Reaction with acid: All metals do not react with dilute acid. When metal reacts with dilute acid, salt of corresponding metal and di hydrogen gas is formed.

Metal + Dilute acid → Salt of corresponding metal + Dihydrogen gas

e.g. Mg(s) +H₂SO₄ (aq) → MgSO₄ (aq) + H₂ (g)

iv) Reaction with Dichlorine: Metals react with dichlorine to form metal chlorides.

Metal + Dichlorine gas → Metal chloride

e.g. Ca(s) + Cl₂(g) → CaCl₂(s)

v) Reaction with Dihydrogen: All metals do not react with dihydrogen because metals donate electrons and dihydrogen does not accept electron.

Metals such as Na, K, Ca combine with hydrogen and form hydrides of that metal.

Active metal + Dihydrogen gas → Metal hydride

e.g. Ca(s) + H₂(g) → CaH₂(s)

The erosion reaction of any metal with water or moisture when it comes in its contact is called metallic corrosion and due to continuous exposure to moist air or water is the reason for metallic corrosion.

Remedies to prevent corrosion:

•Applying paint

It is easy and cheap method to prevent corrosion of iron. The body of a car windows or pillars can be protected against corrosion but it is essential to apply paint at regular intervals.

•Applying oil

Applying oil to the mechanical tools such as hammer, gardener scissors, etc. could be a method for protection of iron from corrosion due to presence of oil layer.

•Galvanisation

It is another method for prevention of iron from corrosion in which very fine layer of zinc metal is coated on the surface of iron. If zinc is removed from the surface of iron, it does not get corroded because zinc is more active metal which spreads and prevents corrosion. It is an effective method of prevention.

•Certain suitable chemicals which are called inhibitors can also be used so that they combine with the surface of metal by chemical bond and prevent corrosion.

•By making alloys which makes them more harder and stronger and prevents corrosion for e.g. steel.

Alloys are the homogeneous mixture of 2 or more metals or metal and non-metals.

By making alloys there are changes in the properties of the element which is advantageous to us such as:

•It makes them hard and stronger. For e.g. steel (alloy of iron and carbon)

•Some of the alloys lowers the melting point which makes them easily fusible and this property is used in solders.

•Alloys of aluminium are light and stronger which are used in aeroplanes.