TyroCity: Chemistry 12 Notes

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:

Copper Sulphate(CuSO4)

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

Copper Sulphate pentahydrate (CuSO4 5H2O) is commonly known as Blue Vitriol. It is obtained in lab by dissolving CuO, Cu(OH)2 or CuCO3 in dil H2SO4. The solution on crystallization gives blue triclinic crystals of CuSO4 5H2O.

CuO + H2SO4 → CuSO4 + H2O
Cu(OH)2 + H2SO4 → CuSO4 + H2O
CuCO3 + H2SO4 → CuSO4 + H2O + CO2
CuSO4 crystallization → CuSO4 5H2O
Blue Vitriol
In large scale, CuSO4 is obtained by reacting scrap copper with hot and dilute H2SO4 in presence of wir.
2Cu + 2H2SO4 + O2 → 2CuSO4 + H2O
Hot & dil

Properties

Hydrated copper sulphate is blue crystalline solid while anhydrous CuSO4 is white amorphous solid.
It is soluble in water.
Action of heat:
Blue vitriol on heating losses 4 molecules of water at 1000c to give monohydrate form and at 2300c to give anhydrous CuSO4.
CuSO4 5H2O 100 → CuSO4H2O 230 → CuSO4
Blue blueish white white

Anhydrous CuSO4 gives back blue vitrial in contact with water so anhydrous CuSO4 is used to detect water.
Anhydrous CuSO4 on further heating decompose forming CuO.
CuSO4 above 230 → CuO + SO3
Black

Action of water:

CuSO4 gives acidiec salt solution due to hydrolysis of Cu++ ion as it. Is salt of weak base and strong acid.
CuSO4 (aq) → Cu++ + SO4
Cu++ + 2H2O → Cu (OH)2 + 2H+

Reaction with KI:

KI reduces CuSO4 to cuprous iodide which appears as white ppt while KI is oxidized to I2

Reaction with NH3:

when NH3 is added to CuSO4 solution, a bluish white ppt of Cu(OH)2 is formed which dissolves in excess ammonia forming tetra amine copper (II) sulphate which is commonly known as Schweizer’s reagent.
CuSO4 + NH4OH → Cu(OH3)4SO4
Bluish white
CuSO4 + NH4OH + (NH4)2SO4 → [Cu(NH3)4]SO4 + 4H2O
Tetra amine copper (ii) sulphate (deep blue)

Uses

It is used as electrolyte in purification of copper & electroplating of Cu.
It is used in making schweizer’s reagent used for mfg of paper.
It is used as pesticide in controlling aphids and fungal growth.

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)

Zinc (Zn)

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

The element Zn, Cd and Hg forms group IIB of the periodic table. These elements do not have partially filled d. orbitals both in metal and metal ion. So, they do not exhibit general properties of transition metals and are called non- typical transition metal.

Occurrence:

Zinc occurs in nature only in combined state. The main ores of zinc are:

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.

Cuprous Oxide Or Red Oxide Of Cupper (Cu2O)

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

It occurs in nature as cuprite. It is obtained by heating copper in air above 11000c.

4Cu+o2 above 11000c → 2Cu2o.

If can also be obtained by reducing alkaline Cuso4. (fehling’s solutional with reducing agents like glucose.

CuSO4+2NaOH → Cu(OH)2+Na2SO4
Cu(OH)2 → CuO+H2O
2CuO + C6H12O6 → Cu2O + C6H12O7

Properties

It is a red amorphous solid insoluble in water.
It dissolves in conc. HCl giving cuprous chloride.

Cu2O + 2Conc.HCl → Cu2Cl2 + H2O

It dissolves in conc. H2SO4 giving copper sulphate and metallic copper

Cu2O + H2OSO4 → CuSO4 + H2O + Cu

Uses

It is used in making ruby-red glass.
It is used in making anti-rust paints.
It is used in preparation of Cu2Cl2.

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.

Numerical Related Hess’s Law

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

1. Calculate the heat of formation of napthalene from the following data.

Alternate solution:
Considering combustion of Napthalence, we have,
H reaction = H formation products – H formation preactants.
-1231.6 = (10 × H formation CO2 + 4 × H formation O2)
-1231.6 = {10 × (-94.405) + 4 × (-68.3)} – H formation of GoH8-O
-1231.6 = -944.05 + (-273.2) – H formation of GoH8
-1231.6 + 944.05 + 273.2 = – H formation of GoH8
-14.35 = – H formation of GoH8
H formation of GoH8 = 14.35 Kcal Jxole-1

2. Calculate the standard heat of formation of CH4 (g) from the following information.

3. Calculate the enthalpy of formation of ethane at 298k, if the enthalpies of combustion at CH2 and C2 H6 are -94.14, -68.47 and -373.3 Kcal respectively.

4. Standard enthalpy of formation of H2O (l), CO2 (g) and C6H6 (l) are -286, -393.5 and +49.02 KJ mol-1 respectively at 298K. Calculate the standard enthalpy of combustion of C6H6 (l) at the given temperature.

5. Calculate the heat of combustion of glucose from the following data.

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,

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.

Ferric Chloride (FeCl2 or Fe2Cl6)

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

Preparation:

Anhydrous FeCl3 is obtained by passing dry Cl2 gas over red hot iron.
2Fe + 3Cl2 → 2FeCl3

Hydrated ferric chloride is obtained by dissolving iron in aquaregia or by dissolving Fe2O3 or Fe (OH)3 in HCl. On crystallization FeCl3 solution gives yellow crystals of FeCl3 6H2O.
2Fe + 9HCl + 3HNO3 → 2FeCl3 + 3NOCl + 6H2O
Fe2O3 + 6HCl → 2FeCl3 + 3H2O
Fe (OH)2 + 6HCl → FeCl3 + 3 H2O

FeCl3 (ag) crystallization → FeCl3.6H2O
Yellow crytals

Properties:

Anhydrous FeCl3 is black amorphous solid while hydrated FeCl3 is yellow crysaline solid.
At lower temperature (4000c) the vapor density of ferric chloxde corresponds to the molecular formula Fe2Cl6. Fe2Cl6 is chlorine bridged dimeric structure.

At higher temperature (7000c), Fecl3 decompose forming ferrous chloride.
FeCl3 above 700 → 2FeCl2 + Cl2

Hydrolysis
The aqueous solution of FeCl3 is acidic due to hydrolysis to form weak base and strong acid.
FeCl3 + 3H2O → Fe(OH)3 + 3HCl
Weak base strong acid
Reaction with potassium Ferro cyanide:
Ferric chloride reacts with potassium ferro cyanide forming a prussiara blue colouration of ferric ferro cyanide.
4FeCl3 + 3 K4 [Fe (CN)6]0 → Fe4 [Fe (CN)6]3 + 12KCl
Prussian blue ferroc ferro cyanide
Reaction with ammonium thiocyanate:
Ferric chloride gives a blood red coloration of Ferric thiocyanate with ammonium thiocyanate.
FeCl3 + 3 NH4CNS → [Fe (CNS)3] + 3NH4Cl
Ferric thiocyanate
Blood red
Reaction with ammonium hydroxide:
Ferric chloride gives a reddish brown ppt of ferric hydroxide with Ammonium Hydroxide solution.
FeCl3 + 3NH4OH → Fe (OH)3 + 3NH4Cl
Ferric hydroxide
Reddish brown

Uses:

It is used in medicine as astrigents and antiseptic.
It is used as mordant in dying.
It is used as a catalyst in friedal craft’s reaction.
It is used to etch metals like Cu, Ag, during making block.

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.