TyroCity: Chemistry 12 Notes

Extraction Of Mercury From Cinnabar

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

1. Concentration

Cinnabar being sulphide is concentrate by froth floatation method. The pulverized are is kept in water containing pine oil & the mixture is agitated by passing compressed air. Ore forms froth with oil and come to the surface and are skimmed off while impurities are left in water.

2. Roasting and distillation

The concentrated are is mixed with 2% coke and fed into shaft furnace through a cup and wine. Arrangement the furnace is heated by pruning fuel and air is below in cinnabar is first oxidized to mercuric oxide which then decompose into mercury the vapor of mercury are condensed in Y-shaped. Earthen condensers cooled by water.

2HgS + O2 → 2HgO + 2SO2
2HgO → 2Hg + O2

3. Purification:
Mercury obtained by above process is not pure and contains impurities like copper (Cu), Zn, Bi, Ag, etc. as impurities. The impure mercury is filtered through daemons leather to remove suspended soiled. After that mercury is dropped through a long tube filled with 5% HNO3 solution. The base metals dissolve in HNO3 as Nitrate.

4Zn + 10 HNO3 → 4Zn(NO3)2 + NH4NO3 + 3H2O
4Cu+ 10 HNO3 → 4Cu(NO3)2 + 2NO + 4H2O

Any mercurous nitrate if from reacts with base metal giving back mercury.

Hg2(NO3)2 + Cu → Cu (NO3)2 + 2Hg

Mercury still contains metal like gold (Au), silver (Ag), Pt, etc. as impurities. These are removed by vacuum distillation where mercury distills leaving other metals.

Properties:

Mercury is a shining metal having density 13.6 gmcm3
It has mpt on -370c and bpt 3570c
It vapourises forming monoatomic mercury molecule and mercury vapour are highly poisonous.

Chemical properties

Action of air
Air does not react with Hg, at normal (ordinary) temperature but on heating, mercury to its boiling point combines with oxygen forming mercuric oxide.

2Hg + O2 → 2HgO

Action of ozone
In an atmosphere of ozone, mercury loses its meniscus due to formation of mercurous oxide. When this mercury is allowed to slide down on glass surface, it leaves mercurous oxide in its trail. This phenomenon is called Tailing of Mercury

2Hg + O3 → Hg2O + O2
Mercurous oxide

Action of acids
dil. HCl and Dil H2SO4 does not reach while dil. HNO3 gives mercurous nitrate.

6Hg + Dil8HNO3 → 3Hg2(NO3)2 + 2NO + 4H2O Mercurous nitrate

Hot and conc. H2SO4 gives SO2 gas along with mercuric sulphate.
Hg + 2H2SO4 → HgSO4 + SO2 + 2H2O
conc.
Mercurous sulphate
Hot and conc. HNO3 gives mercuric nitrate and Nitrogendioxide.
Hg + 4HNO3 → Hg(NO3)2 + 2NO2 + 2H2O
conc.

Conc. HCl alone does not react with mercury but aquaregia dissolves mercury as mercuric (Corrosive sublimate)

HNO3 + 3HCl → NOCl + 2H2O + 2Cl
Hg + 2Cl → HgCl2
Hg + HNO3 + 3HCl → NOCl + HgCl2 + 2H2O

Action of halogen:
Mercury combines directly with halogen to form mercury halides. The compound depends upon availability of halogen.

Hg + Cl2 → HgCl2
Excess Mercuric chloride
2Hg + Cl2 → Hg2Cl2
Limited Mercurous chloride

Action with sulphur
Mercury combines readily with sulphur at ordinary temperature forming mercuric sulphide.
Hg + S → HgS

Uses of mercury

It is used in making thermometer, barometer etc.
It is used in making mercury vapour lamps.
It is used in extraction of gold by amalgumation process.
It is used in manufacture of Caustic Soda (NaOH) by castner kellner process and kellner solvay process
It is used in making amalgam.

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:

Concentration Of Solution

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

Concentration of solution corresponds to the amount of solute present in the given amount of solution. There are different units to explain the concentration of solution.

Units of concentration:
1. Percentage of solution:
It is the no. of part of solute present in 100 parts of solution. Percentage of solution can be expressed either in W/W, W/V or V/V

2. Normality of Solution (eqv.l-1 or N)
It is defined as the no. of gram eqv. of solute present in 1L of its solution.
Mathematically,

A solution is said to have concentration 1 normal (1N), decinormal (N/10) and centinormal (N/100) as 1,0.1,0.01 gm eqv. Of solute are present in 1L of solution respectively.

3. Molarity of solution (moml L-1 or M)
It is defined as the no. of g. mol. Of solute present in 1L of its solution.
Mathematically,

A solution is said to have concentration 1 molar (1M), decimolar (M/10) and centimolar (M/100) as 1, 0.1 and 0.01 g. mol. Of solute are present in 1L of its solution respectively.

4. Gram/L (gL-1)
It is defined as the no. of gm of solute present in 1L of solution. gL-1 can be related to normality (N) and molarity (M) ad thereby normality and molarity can be related to one another and it is reduced as follows:

gL-1 = Normality x eqv. wt. → 1
Similarly,
gL-1 = molarity x mol. Wt. → 2

then from equation 1 and 2. We get,
Normality x eqv. wt. = molarity x mol. Wt.

This expression says, normality and molarity of solution becomes identical only if eq. wt. and mol. wt. are same.

5. Molarity (mol Kg-1 or m)
Molarity is defined as the no. of moles of solute present in 1 kg. of solvent.
Mathematically,

A solution is said to have 1 molar concentration when 1 mole of solute is present in 1 kg of solvent.

6. Mole Fraction (x)
Mole fraction is the fraction of total no. of mole of a compound present in the mixture.
Let us consider a solution containing n1 mole of solvent and n2 mole of solute.

Here, x1 + x2 = 1

7. Part per million (PPM)
Part per million is the no. of part of solute present in 1 million part of solution.

Order Of Reaction

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

Let’s consider a reaction,
A + B → product

The rate of reaction of above reaction is given by rate law expression,

Rate:

where k is constant called rate constant and is rate of reaction when concentration of all reactants is unit molarity (1m). Here m is order of reaction with respect to A, n is order of reaction w.r.t B and (m +n) is overall order of reaction. So, order of a reaction is the sum of the power to which the concentration of reactants is raised in the experimental rate law expression.

Unit of rate constant

Let’s consider a reaction,

A → product

The unit of rate constant depends upon the order of reaction.

For a reaction,

A → product

The rate law expression is,

when n = 0 The reaction is said to be a zeroth order reaction and for such reaction the rate of reaction is independent of concentration of reactant.

E.g.

Enzyme catalysed bio-chemical reaction.
Decomposition of HI on the surface of gold.
Reaction between H2 and Cl2 to give HCl in presence of light.

When, n =1,
The reaction is said to be a first order reaction and for such reaction the change rate is equal to the change in concentration of reactant.

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.

Properties Of Iron

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

1. Action of air:
Dry air has no effect on iron but most air forms a brown layer of hydrated ferric oxide called Rust.
2Fe + O2 + xH2O → Fe2O3.xH2O
Hydrated ferric oxide (Rust)

2. Action of water:
Cold water does not react with iron but when steam is passed over red hot iron,H2 gas is displaced.
Fe+H2O → Fe3O4 + H2
Red -hot steam Ferrosoferric oxide

3. Reaction with non-metals:
Iron reacts directly with non-metals like halogens, sulphur carbon etc. to give respective compounds.
2Fe + 3Cl2 → 2FeCl3
Ferric chloride
Fe + S → Fes
Ferous sulphide.
3Fe + C → Fe3C
Iron carbidc or cementite.

4. Reaction with carbon monoxide:
Iron reacts with CO at 1200C forming iron penta carbonys.
Fe + 5CO 120 → Fe (CO)5
Iron pentacarbonyl

5. Reaction with acids:
With dil. HCl and dil. H2SO4, iron gives ferrous salt along with H2 gas.
Fe + 2HCl → FeCl2 + H2
Dil.
Fe + H2SO4 → FeSO4 + H2
Dil.
with hot and conc. H2SO4, iron gas a mixture of ferrous sulphate and ferric sulphate.
Fe + 2H2SO4 → FeSO4 + SO2 + 2H2O
Conc.
2Fe + 2H2SO4 → Fe2 (SO4)3 + SO2 + 2H2O
with dil HNO3, iron give nitrate and ammonium nitrate
4Fe + 10HNO3 → 4Fe (NO3)2 + NH4NO3 + 3H2O
Dil
with mod conc. HNO3, iron gives Ferric nitrate and NO2 (Nitrogen dioxide).
Fe + 6HNO3 → Fe (NO3)3 + 3NO2 + 3H2O.
with hot and conc. HNO3, Iron does not react due to formation of an inert large of Fe3O4. This is called passivity of iron.

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

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.

Silver Nitrate (AgNO3)

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

Silver Nitrate is commonly known as Lunar caustic.

Preparation
AgNO3 is prepared by dissolving silver metal in dil HNO3. The silver nitrate solution of crystallization gives colorless crystal of AgNO3.
3Ag + 4HNO3 → 3AgNO3 + NO + 2H2O.

Properties

It is colorless crystalline solid soluble in water.
It is highly sensitive to light and when kept in contact with skins it leaves a permanent dark stain.

Action of heat
When silver nitrate is heated first it decomposes forming silver nitrite which on further heating decompose giving silver metal.
2AgNO3 → 2AgNO2 + O2
AgNO2 → Ag + NO2

Precipitation reaction
AgNO3 gives precipitate with halide ion (Cl, Br & I ) and from color of precipitate the halide ion can be identified.
Cl + AgNO2 → AgC + NO3
Curdy white
Br + AgNO2 → AgBr + NO3
Pale yellow
I + AgNO2 → AgI + NO3
Yellow ppt
Ammonical Silver Nitrate [Tollen’s reagent] is used to detect reducing groups in organic compounds like aldetyde. The reducing agent reduces tollen’s reagent to metallic silver which deposits in test-tube forming silver mirror.
Ag2O + HCHO → 2Ag + HCOOH
Toller’s reagent

Uses

It is used in making silver halides used in photography.
It is used in making inks and hair dye’s.
It is used in making silver mirror.
It is used in lab as analytical reagent.

Some Special Steels

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

Zinc Oxide (ZnO)

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

ZnO is commonly known as philosopher’s wool or zinc white or china white.

Preparation:

It can be obtained by heating zinc in air.

2Zn + O2 → 2ZnO

It can also be prepared by decomposition of zinc carbonate. Zinc nitrate, zinc sulphate, etc.
ZnCO3 → ZnO + CO2
2Zn(NO3)2 → 2ZnO + 4NO2 + O2
ZnSO4 → ZnO + SO2

Properties:
It is light white amorphous solid which becomes yellow on heating and again on cooling.

When heated with cobalt nitrate, it gives a green compound known a Rinmanr’s green, It is a mixed oxide and is used as green pigment.

2Co (NO3)2 → 2CoO + 4NO2 + O2

ZnO + CoO → CoZnO2

Cobalto zincate (Rinmann’s green)

ZnO is an amphoteric oxide. And can react with both acid and alkali forming saltand water.

It is insoluble in water but dissolves in acid giving respective salts.

Use:

It is used as pigment in making white colored paints.
It is used for surgical dressing. (Sterilizing agent).
It is used in preparation of Rinmann’s grice used as pigment.

Bond Energy Or Bond Enthalpy

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

Bond energy of a bond is amount of energy required to break 1 mole of a bond in gaseous state or energy released when one mole of a bond is formed in gaseous state.

In terms of bond energy,
Hreaction = Heat absorbed – Heat released = bond energies of reactants – bond energies of products

Estimate the enthalpy change for the reaction

Sol:
The amount of energy released during formation of 2moles of H-Cl bond = 2 × 430 = 860 KJ

H reaction = Energy absorbed – Energy released
= 618 – 860
= -182 KJ

Calculate the enthalpy change for the hydrogenation of ethane gas.

Given, bond energy of H -H bond = 435 KJ mole-1

Bond energy of C – H bond = 413 KJ mole-1

Bond energy of C -C bond = 347 KJ mole-1

Bond energy of C=C bond = 615 KJ mole-1

The amount of energy absorbed during reaction
= 413 × 4 + 615 + 435
= 2702 KJ

Energy released during reaction
= 6 × 413 + 347
= 2825 KJ

H reaction = 2825 – 2702 KJ = -123 KJ