TyroCity: Chemistry 12 Notes

Laplace – Lavoiser Law Of Thermo Chemical Reaction

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

The amount of heat for the reverse of a reaction will be equal but will have opposite sign.

Cupric Oxide Or Black Oxide Of Copper (CuO)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is obtained by heating copper in air above 9000c
Cu + O2 above 900 → 2CuO

It can also be formed by heating cupric hydro oxide, cupric carbonate or cupric nitrate.
Cu(OH)2 → CuO + H2O
CuCO3 → Cuo + CO2
2CuO(NO)3 → 2CuO + 4NO2 + O2

Properties

It is a black amorphous solid insoluble in water.

It reacts with acids forming corresponding salts. cuprous chloride.
CuO + 2HCl → CuCl2 + H2O
Cupric Chloride
CuO + H2SO4 → CuSO4 + H2O
Copper Sulphate
CuO + 2HNO3 → Cu(NO3)2 + H2O
Cupric Nitrate

It is reduced by reducing agents like H2 CO etc. to copper.

CuO + H2 → Cu + H2O
Heated
CuO + Co → Cu + CO2
heated

Uses

It is used in making colored glass.
It is used to remove sulphur from petroleum.

Extraction Of Iron From Haematite

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

1. Concentration:
Haematite ore being oxide ore is concentrated by gravity separation process using hydraulic separator. The oxide is being heavier settles to the bottom while lighter impurities come to the surface and is removed.

2. Calcination:
The concentrated ore is heated in limited supply of air on the shallow hearth of Reverberatory furnace during calcination, flowing changes occur.

Moisture and volatile impurities are driven out.
Non-metallic impurities like s, p, etc are removed as their oxides.
S + O2 → SO2
P4 + 5O2 → 2P2O5
If any carbonate is present then it dissociates to give oxide.
FeCo3 → FeO + Co2

3. Smelting:
The calcined ore is mixed with lime stone (CaCO3) (Flux) and ore in the ratio of 8:1:4 and charged into blast furnace. The blast furnace is cylindrical steel vessel limed 6m in diameter. On passing Pre heated compressed air inside the furnace, four distinct zones are formed.

Zone of reduction combustion:
This zone lie at the bottom of the blast furnace where carbon burns in presence of pre heated air forming CO2 and heat.
C + O2 → Co2 + heat
Here, the temp is maintained above 15000c. This produces the energy required for the smelling of iron.

Zone of fusion:
This zone lies above zone of combustion. Here upcoming CO2 is reduced by red-hot coke to carbon monoxide. The reaction is endothermic and temp falls to 12000 -13000 c
Co2 + C → 2CO – heat
Red-hot
The spongy iron formed in zone of reduction melts here and any oxide escaped reduction is reduced here.
2Fe2O3 + 3C → 4Fe + 3CO2

Zone of slag formation:
This zone lies above zone of fusion and it has temp of about 10000c. In this zone calcium carbonate dissociate forming can (calcium oxide) which combines with silica (SlO2) present as impurity in Haematite forming calcium silicate (CaSiO3) as slag.
CaCo3 → CaO + CO2
CaO + SiO2 → CaSiO3
Calicum flicate (slag)
The slag is lighter than molten iron and to floats on the surface of the iron. The formation of prevents the oxidation of iron.

Zone of reduction:
This is the most important zone and has temperature of 600-7000c. In this zone Fe2O3 is reduced to iron by co in three steps.
3Fe2O3 + CO → 2Fe3O4 + CO2
Fe3O4 + CO → 3FeO + CO2
FeO + CO → Fe + CO2
(Solid state)
From the bottom of blast furnace, molten slag and molten iron are tapped out. This iron is impure and is called cast-iron or pig-iron.

Copper

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Symbol: Cu (Cuprum)

At. No.: 29

At mass: 635

Electronic Configuration:

Occurrence
Copper occurs in both native state and combined state. The chief ores of copper are:

Mohr’s Salt Or Ferrous Ammonium Sulphate FeSO4(NH4)2 SO4.6H2O)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Hydrated ferrous ammonium sulphate is commonly known as mohr’s salt .It is prepared by crystallization of equimolar solution of FeSO4 and (NH4)2SO4.

FeSO4(aq) + (NH4)2SO4 crystallization → FeSO4 (NH4)2SO4.6H2O.
Mohr’s salt
This double salt is more stable than FeSO4 alone and is used as reducing agent in redox fitration. During redox reaction Fe+2 ions mohr’s salt is oxidised to Fe+3 ions.

(Properties same as FeSO4. 7H2O)

Rusting

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

The chemical corrosion of iron by oxidation with moist air to give hydrated ferric oxide is called resting and the produce is rust. The nesting process is accelerated by acidic oxide like CO2, SO2, NO2, etc.
2Fe + O2 + xH2O → Fe2O3. xH2O
Rust
There are many theories to explain the nesting of iron is any which most reliable theory is electrochemical theory.

Acc. to this theory, rusting of iron occurs due to formation of galvanic cell in the iron. At anode, iron atom oxides to Fe++ ion by losing 2 electrons.

At anode, Fe → Fe++ + 2e
The electon moves to cathode where oxygen reduces to OH by gaining electron.
At cathode=12O2 + H2O + 2e → 2OH

Fe++ and OH– ion combines forming Fe(Oh)2.
Fe+2 +2OH → Fe (OH)2
Ferrous wmpound are unstable so Fe(OH)2 is oxided by air in presence of water to Fe (OH)3. Which then decompose forming Ferric oxide which is rust.
2Fe(OH)2 + H2O +12O2 → 2Fe (OH)3
2Fe (OH)3 → Fe2O3+3H2O.
This theory is supported by fact that analysis of rust shows presence of Fe+3 stages.

Prevention of rusting:
This phenomenon can be prevented by:

By applying layer of enamel, grease oil etc.
By galvanisity iron by zinc.
By making passive by dipping is conc. HNO3 or by passing steam over red hot iron.
By cathodic protection, this process is generally used in ships Iron is kept in contact with more electropositive metals like Zn, Al, Mg, etc. which acts as anode where iron is protected as cathode. The metal used as anode is called sacrificial anode.

Silver (Ag)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Symbol : Ag (latin, Argentum)
Atomic number : 47
Atomic mass : 108 amu

Occurrence:
It occurs in both combined step and native state. The chief ores of silver are:

Thermodynamic Equilibrium

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

The system is said to be in thermodynamic equilibrium if it attains thermal, mechanical, and chemical equilibrium at a time with surrounding.
Thermal equilibrium means temperature remaining constant.
Mechanical equilibrium means pressure remaining constant.

Chemical equilibrium means composition/mass remaining constant.

First Law Of Thermodynamics

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Total energy in the universe remains constant.
Energy can neither be created nor be destroyed but can be transferred from one form to another.
When Q amount of heat is supplied to the system, some part of it is used up to increase in its internal energy and remaining some part of it is used up for work done.

i.e. Q=∆E+W………………. (1)
If work is done by the system.
Q=∆E-W………………. (2)
If work is done on the system.
Where, Q= heat supplied
W=work done
∆E=change in internal energy.
∆E at constant volume
We have, from first law of thermodynamics;
Q=∆E+W
Q=∆E+P∆V
At constant volume, ∆V=0
So, Q=∆E
It means, at constant volume condition, the total amount of heat supplied is equal to change Internal energy of system.
∆E at adbiatic condition
We have, from first law of thermodynamics;
Q=∆E+W
At adbiatic condition, Q=0
So, -W=∆E
It means, at adbiatic condition, the work is done by utilizing the Internal energy of system.

Advantages of first law of thermodynamics

Total energy of the universe remains constant.
Different forms of energy are inter-convertible.
When one form of energy disappears, an equivalent amount of energy in another form appears.

Disadvantages of first law of thermodynamics

It doesn’t tell the extent and direction of the convertibility of one form of energy to another.
It doesn’t tell why chemical reactions do not proceed to completion.
It doesn’t tell why natural processes are unidirectional.
It doesn’t explain the feasibility and spontaneity of a process.
It says the equivalency of work and heat. But it has been observed that the work can be completely transformed into heat but heat cannot be transformed into work without permanent change in the system or surrounding which is not explained by the law.

Extraction Of Copper From Copper Pyrite

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

The principal ore of copper is copper pyrite and copper is extracted from this ore. The different steps in extraction of copper are:

Crushing and concentration:
The ore obtained from mines are broken down into small piece by jaw crusher and then pulverized. The ore being sulphide ore is concentrated by froth floatation process. Pulverized ore is kept in water containing pine oil and the mixture is agitated by passing compressed air. Ore forms froth with pine oil and comes to the surface and is skimmed off while impurities are left in water.

Roasting
The concentrated ore is heated in excess supply of air on the hearth of reberberatory furnace below its melting point. The different changes during roasting are:

Moisture and volatile impurities are driven out.
Non-metallic impurities like sulphur, phosphorous, arsenic etc. are removed as their oxides.

Smelting
The roasted ore, coke and silica (flux) is charged a water jacketed blast furnace when hot air is passed into blast furnace. Fes if oxidized to FeO which combines with S1O2 to form ferrous silicate as slag.

As long as Fes is present in the mixture Cu2O can’t be formed as copper has higher affinity for sulphur than oxygen. In molten state FeS & Cu2S are missible and the molten mixture of Cu2S and FeS is called copper malte. The lower end of blast furnace has two openings for slag and copper matte.

Fig: Blast Furnace for extraction of copper

Bassemerisation
The molten matte is mixed with little silica and charged into a Bessemer converter. Lined internally by basic lining of CaO or MgO. Hot air is blown into the mixture which converts remaining FeS. To FeSiO3.

The reaction is highly exothermic and copper obtained is in molten state. During solidification, SO2 escapes forming blisters on the surface of metal. This variety of copper containing about 2% of impurity is blister copper.

Refining:
Blister copper consists of about 2% of impurities consisting of cliver, Glod, Zinc, Nicket etc. It is mostly purified by electrolytic method. A block of impure copper is anode, a strip of pure copper is cathode while solution of CuSO4 containing dil H2SO4 is e;ectrolyte. On passing current, impure copper dissolves and equivalent amount of pure copper is deposited at cathode. Impurities are collected below anode as anode mud.

Physical Properties:

It is a transition metal having characteristic red color.
It is highly malleable & ductile and has high electrical and thermal conductivity
It has high melting point 10830c and bpt 2320c
It has specific gravity 8.93

Chemical properties

Action of air:
Dry air has no effect but moist air containing CO2gas forms a green layer of basic copper carbonate.

Action of water:
Water has no effect on copper.

Action of Alkalis:
Alkalis has no effect on copper.

Action of Acids:
** 1. With HNO3**
dil HNO3 does not react with copper while moderately conc. HNO3 (1:1) is reduced to Nitric oxide by copper.

2. With H2SO4

dil. H2SO4 alone does not react but hot dil. H2SO4 in presence of air gives CuSO4

3. With HCl
Copper reacts with hot and conc HCl in presence of air forming cupric chloride.

Displacement reaction:
Copper can displace metals lying below it in electrochemical series from their salt solution.

Uses of copper:

It is in making electrical cables.
It is used in making coins.
It is used in making allays like brass, German Silver.
It is Rold Gold, constantan, bell metal etc.
It is used in making utensits.
It is used in making scientifi equipments like calioriemeter boilers etc.

Enthalpy (H)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

It is the sum of internal energy and product of pressure and volume.

i.e. H=E+PV…..(1)
Here, E, P & V all are state function so H is also the state function.
Being a state function it depends upon initial and final state and also its absolute value cannot be determined however change can be measured.
Now, ∆H=Hp-Hr…………(2)
Where, Hp= enthalpy of product
Hr= Enthalpy of reactant
∆H at constant pressure
We have, from first law of thermodynamics;
Q=∆E+W
Q=∆E+P∆V….(1)
Also, H=E+PV……..(2)
At constant pressure, Q=Qp
So, equation (1) becomes,

Qp=Ep-Er+P(Vp-Vr)
Qp=Ep+PVp-(Er+PVr)
Qp=Hp-Hr
Qp=∆H
It means, heat of reaction at constant pressure is equal to change in enthalpy of reaction.

Half Life (t1/2)

Chemistry 12 Notes — Sun, 08 Apr 2012 05:41:42 +0000

Half Life of a reaction is time required to reduce the initial concentration to half. The half-life of a reaction depends on the order of reaction. The variation of half-life with order is given as:

Integrated rate law expression

For Zeroth order reaction

For first order reaction

Integrating on both sides, we get,

So, half-life of first order reaction is independent of initial concentration.

Numerical
The half-life of a first order reaction is 50 mins. Calculate the time required to complete 75% of the reaction.
Given,

Again,
initial concentration (a) = 100 (let) then
at time t,

Concentration left (a-x) = 100-75 = 25
We have,

Calculate the half period of first order reaction when rate constant is 5 year-1.
We have,
For 1st order reaction
t1/2 = 0.693/5
= 0.1386 year