TyroCity: Chemistry 12 Notes

Extraction Of Zinc From Zinc Blende

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

Concentration:
Zinc blende is concentrated by floath floatation process. The pulverized ore is kept in large tank containing water and pine oil. The mixture is agitated by passing compressed air. Ore forms froth and comes to the surface while impurities are left in water.

Roasting:
The concentrated are is heated in excess supply of air above 9000c on the hearth of reberveratory furnace. During roasting. Zinc sulphide is converted to Zinc Oxide.
2ZnS + 3O2 → 2ZnO + 2SO2

Small amount of ZnS may be oxidized to ZnSO4 but above 9000c , ZnSO4 decompose forming Zinc Oxide (ZnO)
ZnS + 2O2 → ZnSO4
ZnSO4 above 900 → 2ZnO + 2SO2 + O2

Reduction (Smelting):
ZnO obtained during roasting is mixed with coke and heated strongly where ZnO is reduced to Zn by carbon.
ZnO + C → Zn + CO
The reduction is done in vertical refort. In this process roasted are mixed with coke in the ration of 2:1 and small briquets are made. These briquets are fed into vertical report furnance, from the charging door. The report is heated externally by burning produce gas (w+N2) to about 14000c. The vapour of zn is camed to condenser where it condenses to give molten zinc called spelter zinc.

Purification:
Zinc spelter contains pb, fb, cd, as, etc. as impurities. Impure zinc can be purified by following methods.

1. By fractional distillation:
The bpt of Pb, Fb are higher than that of zinc while that of cadmium, arsenic are lower than that of zinc. When distillation is carried out around 1000°c, zinc, Cd, As, etc. distill off leaving Pb and Fe the distillate is then heated to 800°c where cd and as distill off leaving pure zinc. This sample of Zn is about 99% pure.

2. By electrolysis:
Zinc of higher purity can be obtained by electrolysis. Pure zinc rod is used as cathode while a block of impure zinc is used as anode. A mixture of ZnSO4 and dill H2SO4 is used as electrolyte. On passing current impure zinc dissolves and equivalent amount of pure zinc is deposited at cathode.

Physical properties

It is a blueish white lusticous metal.
Zinc is brittle at ordinary temperature but it becomes malleable from 100-150. c then again it becomes brittle.
It melts at 420. c and boils at 900. c and has sp. Gravity 7.13.

Chemical properties
1. Action of air:-
Dry air has effect on zinc but in moist air, zinc forms a protective layer of basic zinc carbonate.
Zn + O2 + H2O + CO2 → ZnCO3.Zn (OH)2
When heated in air, zinc burns greenish blue flame forming clouds of light, white power of zinc oxide which is commonly known as ‘philosopher’s wool. Beside this name, other common names are ‘Zinc white and china white.
2Zn + O2 → 2ZnO

2. Action of water:-
Pure zinc does not react with water but impure zinc displaces hydrogen gas. Zn-inc reacts with hno3 in four different concentrations giving different reduced product.
Zn + H2O → ZnO + H2

3. Action with acids:
Dilute H2SO4 and dil. HCl gives H2 gas with zinc
Zn + dil. H2SO4 → ZnCl2 + H2
Zn + dil. HCl → ZnSO4 + H2

With hot and conc. H2SO4 zinc gives SO2 gas
Zn + 2H2SO4 → ZnSO4 + SO2 + 2H2O

Zinc reacts with HNO3 in four different conditions giving different product:

With very dil. HNO3
With very dil. HNO3, Zn gives ammonium nitrate
4Zn + 10HNO3 → 4Zn(NO3)2 + NH4NO2 +3H2O

With dil. HNO3
Zinc reduces dil. HNO3 to nitrous oxide (N2O)
4Zn + 10HNO3 → 4Zn(NO3)2 + N2O +5H2O

With modrately conc. HNO3
Zinc reduces moderately conc. HNO3 to NO (nitric oxide)
3Zn + 8HNO3 → 3Zn(NO3)2 + 2NO2 +4H2O

With conc. HNO3
Zinc reduces conc. HNO3 to NO2 (nitrogen dioxide)
Zn + 4HNO3 → Zn(NO3)2 +2 NO2 +2H2O

4. Reaction with Alkalies:-

Zinc readily dissolve in hot and conc. solution of caustic bases like NaOH , KOH, etc giving hydrogen gas.
Zn + NaOH → Na2ZnO2 + H2
Zn + KOH → K2ZnO2 + H2

5. Displacement Reaction:-

Zinc can displace less electropositive metals from their salt solution
Zn + CuSO4 → ZnSO4 + Cu
Zn + 2Na[Au(CN)2] → NA2[Zn(CN)4] + 2Au

Uses of zinc:

It is used for galvanization of iron.
It is used in making alloys like Brass. German metal, German silver, etc

Galvanization
The process of applying a coat of zinc on base metal like iron is galvanization Iron is galvanized to protect iron from resting the galvanization is done in following steps.

Cleaning and picking:
Before applying zinc coat on iron, the surface of iron should be clean. The cleaning is done first by sand blast and then washed by dipping in diluted acid. The process of cleaning iron by using dil. acid is called picking.

Applying of zinc coat:
The coat of zinc can be applied on iron surface by 3 methods.
By electroplating:-
Zinc can be electroplated on iron by keeping iron article as cathode, zinc as anode and znso4 solution as electrolyte. On passing current a layer of zinc is coated on iron article.
By metallizing:-
Zinc can be directly applied by dipping iron article in molten zinc this process is generally used for galvanization of iron sheets. Iron sheets are dipped in molten zinc bath & then passed through huge rollers that distributes zinc coat equally.
By sherardizing:-
The process is used for galvanization of small iron articles like nail, screws etc. In this process iron article are mixed with zinc dust and then heated in enclosed vessel for few hours when coat of zinc is applied on iron.

Volumetric Analysis Formulae

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

This relation tells that the combining mass ratio of reactants is always in the ratio of their equivalent masses. This law is also termed as law of chemical equivalence.

Atomic mass = eqv. Mass x valency
G. eqv. / eqv. = Equivalent mass of substance expressed in grams is 1 g. eqv. Or 1 eqv.

Eqv. Mass of a compound.

Where basicity of acid is defined as the no. of H+ ions displaced or OH– ions combined per molecule of the acid.
eg. Eqv. Mass of H2SO4 = 98/2 = 49

Where acidity of the base is defined as the no. of H+ ions combined or OH– ions displaced per molecule of the base.
eg. Eqv. Mass of Ca(OH)2 = 74/2 = 37

eg. Eqv. Mass of Na2Co3 = 106/2 = 53

eg. Eqv. Mass of CO3— = 60/2 = 30
Eqv. Mass of Na+ = 23/1 = 23
In the case of acid, base and salt, the eqv. Mass can be obtained by the summation of positive and negative radical.

Manufacture Of Steel

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

By Bessemerisation process:
Principle:
In bessemerisation process, the impurities present in cast iron are removed by air oxidation and calculated amount of carbon is added in the form of spigelesien (Fe + Mn +C) is added to obtain Steel. The lining of Bessemer converter depends upon presence or absence of phosphorous. If phosphorous is present, then basic lining of CaO or MgO is used and if phosphorous is absent, then acidic lining of SiO2 is used. The reactions occurring during manufacture of steel are.

2C +O2 → 2CO
S + O2 → SO2
Si + O2 → SiO2
2Mn + O2 → 2Mno
MnO + SiO2 → MnSiO3
Manganous silicate (slag)

If phosphorous is present,

4P + 5O2 → 2P2O5
P2O5 + 3CaO → Ca3(PO4)2
Calcium phosphate (thomas slag)

Process:
Molten cast iron is kept in Bessemer converter lined internally by basic lining (if phosphorous is present) or acidic lining (if Phosphour is absent) and blast of air is passed into the mixture. At first impurities other than carbon are oxidized. Then carbon is oxidized to carbon monoxide which burns with light blue fame at the mouth of bessemer converter. When the flame dies out, calculated amount of spigelesin is added and mixed by passing air for some time. Then steel is manufactured. The process is completed in 15-20 minutes and the batch size is 500-600Kgs. The quality of steel obtained by Bessernerization process is not uniform. During the process some amount of Iron is lost as slag.

By Siemen Martin’s process or open hearth process:
Principle:

In open hearth process, the impurities present in cast iron are removed by oxidation by haematite. The percentage of carbon is decreased by adding scrap iron. The heat required for the process is obtained by burning per-heated producer gas (Co+N2) by regeneration of heat economy Depending upon the impurities the lining of hearth is acidic (If phosphorous is absent) or basic lining (if phosphorous is present). The percentage of carbon is maintained by adding required amount of splgelesien. The reactions during manufacture of steel are.

3C + 2Fe2O3 → 4Fe + 3CO2
3S + 2Fe2O3 → 4Fe + 3SO2
3Si + 2Fe2O3 → 4Fe + 3SiO2
SiO2 + Cao → CaSiO3

If phosphorous is present,

6P + 5Fe2O3 → 10Fe + 3P2O5
P2O5+3CaO → Ca3(PO4)2

Process:

Mixture of cast iron scrap iron , haematite and small amount of lime is kept on hearth of open hearth furnace & mixture is healed by burning producer gas by regenerative system. The outgoing hearth gas pre. Heats the incoming producer gas which an combustion can generate higher temperature. The slag formed is removed and a small amount of steel is withdrawn from the hearth and is analyzed. The percentage of carbon in steel can be increased by adding spigelicien and can be decreased by adding scrap iron. The process is slow and takes about 8-10 hours and quality steel is better as sample can be analyzed.

The advantages of open hearth process over bessemerization process are as follows:

The quality of steel is uniform.
Substance like Haematite, scrap iron is converted to valuable steel.
The loss of iron is very small.
The batch size in open hearth process is very large compared to bessernerisation process.

Varieties Of Iron

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

Iron is used in three commercial varieties.

1. Cast iron or pig iron:
It is the most impure form of iron and contains two-five percent impurity mainly carbon. This from is hard and brittle. It is used in making gutter pipes, furniture gutter cover (manhole)

2. Wroght iron:
It is the purest form of iron and contains 0.12-0.25% impurity. It is soft and malleable. It is used in black smith. It is used in making agricultural tools, chains, anchor, etc.

3. Steel:
It is intermediate form of iron and contains 0.5-1.2% impurity mainly carbon. It is mostly used as construction materials, etc.

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:

Thermodynamic Processes

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

Isothermal process
Any physical or chemical process in which the temperature remains constant during the state change is called isothermal process.
Here, ∆T=0

Adbiatic process
Any physical or chemical process which takes place without flow of heat in or out of system during the state change is called adbiatic process.
Here, ∆Q=0

Isobaric process
Any physical or chemical process in which the pressure of the system remains constant during the state change is called isobaric process.
Here, ∆P=0

Isochoric process
Any physical or chemical process in which the volume remains constant during the state change is called isochoric process.
Here, ∆V=0

Transition Metals & Iron

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

The elements of ‘d’ block of periodic table including elements of Group IB to vii B. And viii are transition metals some important characteristics of transition metals are:

They have general configuration (n-1)d1-10 ns1-2 . They have partially filled valence shell and penultimate shell.
Transition metals have strong metallic bond, so they are heavy and herd. They have high mpt and bpt.
They are highly malleable and ductile they have high electrical and thermal conductivity.
They can absorb large quantity of the gases on their surface and this phenomenon is called occlusion. Because of this property these metals are used as catalyst in gaseous reaction.
Transition metals show variable oxidation state. For 3d, series, +2 is common O.S.

Eg. Sc → +2 and +3
Cu → +1 and +2
Mn → +2,+3,+4,+5,+6 and +7
MnSO4, Mn2O3, Mno2, Mn2o5, K2Mno4/HMno4

Transition metal forms colored compounds. The color of compounds is determined by number of unpaired electrons in d-orbital species with some no of unpaired electrons have same color.
Eg. V4 + → Cu4
(Ar)3d1 → (Ar)3d9 both have blue color.
1 Unpaired e+ 1 unpaired e–
They transition metal and metal ions show paramagnetic nature. The magnetic moment depends upon the number of unpaired electrons in d-orbital.
Transition metal ion can from complex with ligands. The central metal provides empty orbitals into which ligands donate tone pair of electrons forming co-ordinate co-Volant bond.

Arhenius Equation Dependence Of Rate On Temperature

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

The variation of rate or reaction on temperature is given by Arhenius equation. This eqn is:

where,

k = Rate constant
Eact = Activation energy
R = Universal gas constant
T = Temperature in Kelvin
A = Constant called Arhenius factor

In a graph of lnk is plotted against 1/T it gives a straight line having y-intercept value lnA and slope -Eact/RT.

This shows that the rate constant is directly proportional to rate of reaction increase in temperature causes increase in rate of reaction.

If k1 and k2 are rate constant of a given reaction at T1 & T2.

Then,

From equation (i) and (ii) we get,

Introduction To Thermodynamics

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

Energy is the capacity of doing work and it has different forms. Energy can neither be created nor be destroyed but can be transferred from one form to another.
Thermodynamics is a branch of science that deals with the inter-conversion of one form of energy into another. In another word, it is the relation between energy change and chemical reaction.
Different terms used in thermodynamics:
System
The part of universe which is our observation is called system.
Surrounding
The part of our universe beyond the system is called surrounding.
Boundary
The part of universe that separates system from surrounding is called boundary.

Types of system
Open system
The system which can exchange both matter and energy to the surrounding is called open system.eg water kept in open vessel.
Closed system
The system which can exchange energy but not matter to the surrounding is called closed system.eg water kept in closed vessel.
Isolated system
The system which can neither exchange energy nor matter to the surrounding is called isolated system.eg water kept in thermos.

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.

Rate Of Reaction And Stoichiometric Coefficient

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

Let’s consider a reaction

N2 + 3H2 → 2NH3

The rate of reaction can be expressed as,

Here, during disappearance of 1 mole of N, 3 mols of H2 are disappeared. So, the rate of disappearance of H2 is 3 times the rate of disappearance of N2.

The disappearance of 1 mole of N2 gives 2 moles of NH3. So the rate of formation of NH3 is 2 times the rate of disappearance.

The equivalent rate of reaction is,

Therefore, the equivalent rate of a reaction is obtained by dividing the rate of each species by its stoichiometric coefficient,

aA + bB → cC + dD

The equivalent rate of reaction is,

For the reaction,
H2 + I2 → 2HI

Express the rate of reaction in terms of all species for decomposition of N2O5. If the rate of formation of O2 is 2× 10-4 mol lit-1 S-1 calculate the rate of disappearance of N2O5 and rate of formation of N2.

Sign Convention Of Heat And Work

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

1. Heat (q)
Case I:
When heat is absorbed by the system, q = +ve.

Case II:
When heat is released by the system, q = -ve.

2. Work (w)
Case I: (Work of Expansion)
When work is done by the system, w = +ve.

Case II: (Work of Compression)
When work is done on the system, w = -ve.