Chemistry Solved Past Paper 2nd year 2013 Karachi Board

SECTION ‘A’ (MULTIPLE QUESTIONS ANSWER)

1. Choose the correct answer from the given options:

i) The formula of Hypochlorous acid is:
* HOCI
* HCIO
* HCIG.J
* HCl04

ii) The etal ion having the highest number of unpaired electrons is

* Mn+2
* Fe+2
* Co+2
* Ni+2

iii) The chemical name of laughing gas is:
* Nitric oxide
* Nitrous oxide
* Nitrogen trioxide
* Nitrogen pentoxide

iv) This has the minimum hydratio energy:
* Na+
* K+
* Rb+
Cs+

v) Cycfoalkanes have the general formula:
* CnH2n+2
* CnH2n-2
* CnH2n
*CnH2n+4

vi) Glycogen is a:
* 0 osaccharide
* 0igosaccharide
* Polysaccharide
* Disaccharide

vii) This gas was used in the First World war.
* Phosgene gas
* Mustard gas
* Coal gas
* Ammonia gas

viii) The hybridization in the Carbon atom of Carbonyl group i~:
* sp
* sp2
* Sp3
* d2sp3

ix) All no e gas fulfill the Octet ru e except:
* Kr
* He
* Ne
* Ar

x) The atomic number of an e ernent be ongi g to group VA and 3rd period is:
* 7
* 13
15
* 23

xi) Ele ent of group IB are called:
* normal elements
* Rare Earth metals
* Coinage metals
* Alkali metals

xii) Hydride ion and Helium atom have the same:
* number of protons
* Number of e elctrons
* number of neutrons
* valency

xiii} The number of neutrons in Protium is:
* zero
* 1
* 2
* 3

xiv) The element having the s~bol ‘Ga’ belongs to this family:
* Carbon
* itrogen
* Boron
* Beryllium

xv) On burning in excess of Oxygen. Sodium forms its:
* superoxide
* peroxide
* monoxide
* dioxide

xvi) A mixture of Aluminium nitrate and Aluminium powder is called:
* Duralumin
* Ammonal
* Camallite
* Alum

xvii) C32B,011.5H20is the chemical formula of:
* Cryolite
* Colernanite
* Bauxite
* Borax

SECTION ‘B’ (SHORT QUESTIONS ANSWER)

INORGANIC CHEMISTRY

2.i) (a) Give the valence shell electronic configuration of the following groups:
IlA and lB .
IIA and lB
IIA = ns2
18 = ns’, (n_i)d1o
IVA and VIB
Ans: IVA and VIS
IVA = ns2, np2
VI~ = ns’, (n _1)d5
(b) Define the following with examples:
Dobereiner’s Triads
Ans: Dobereiner arranged the elements in a group of three i.e. mad.
According to him
* In a triad, the atomic mass of the central element is approximately same as the arthematic mean of the other two elements·

daigram

daigram

Newland’s Law of Octaves
Newland an English chemist, arranged, the elements in the increasing order of their atomic weights. According to him.
“When elements are arranged in the ascending order of their atomic weights, the 8th elements starting from 1st  resembles the first in physical and chemical properties

(a) Differentiate between the natural isotopes of Hydrogen.

table

table

ii) (b) Interstitial Hydrides are not true chemical compounds. Comment.
Transition metals adsorb H2 gases molecule on Intrestitial spaces ,(empty spaces between atoms) It is called interstitial Hydrides, Properties of these hydrides apparently those of pure metals. Thats why they are not true chemical compounds.
iii) Give equations for the following;
* Reaction of Ferric oxide with Aluminium
2AI + Fe203 ~ 2Al203 + 2Fe
Reaction of litharge with Sodium chloride.
Ans: 5PbO + H20 + 2NaCI ~ 2NaOH + PbCI2.4PbO
Reaction of Benzene with Sulphuric acid
Ans: CsHs + H2S04~ CSHSS03H + H20
* Reaction of Sodium dichromate with Potassium chloride
Ans: Na2Cr207 + 2KCI ~ 2NaCI + K2Cr207
iv) What is Allotropy? Describe amorphous form ofSulphur.- lve reasons for its softness and elasticity. I
Ans: Allotropy: The existence of element in more than one form is
known as allotropy. Allotropic forms of sulphure:
There are two allotropic forms of sulphur.
(a) Crystalline (b) Amorphous
(b) Amorphous form of Sulpher:
When sulphur is heated up to its bOiling point & quickly proved into cold water then a rubber like plastic sulphur is obtained.
Structure:
Its structure consist of long chains’S’ atoms coiled up its elasticity is due to uncoiling of long sulphur chains and then recoiling of on release of tension, hence it can be stretchable.

Chain of Sulphur atoms

Chain of Sulphur atoms

Properties:
1. It is black rubber like material.
2. It is non-crytalline forms-of sulphur.
3. It is insoluble in water but soluble in CS2.

v) Give reasons:
The elements of a group in the periodic table have the same valence shell electronic configuration.
Since the properties of element have a periodic function of their atomic no (Z), the electronic configuration vary with increasing atomic no. in periodic maner. Hence In a group elements shows same valence shell electronic configuration.

Alkali metals cannot be used in voltaic cell.
Alakli metals shows high oxldation.electrode potential. Hence it can not be used in voltaic cell, which has water as solvent, to avoid the reaction of metal with water.

In d block elements, 4s orbitals are filled prior to 3d orbitals
but 4s electrons are lost first in ionisation.
4s orbitals has less energy then 3d, So it filled prior to 3d. But 45 orbit is outer most that why electron lost first fram 4s orbit in Ionization.

Ligands are generally called Lewis bases.
Lewis Base are electron doner since ligands are also electron doner to the transition metal incomplete compounded. Hence It is also called Lewis Base.

vi) Explain the extraction of Sodium metal by the electrolysis of
molten Sodium chloride.
Introduction:
The electrolysis of molten NaCI for industrial production of Na-metal
involves the reduction of Na+ ions. at cathode. This is carried out in
‘Down’s cell.
Chemistry of Cell (Down’s Cell):
In this process a mixture of NaCI and CaCI2 is electrolyzed in a cylindrical outer iron cell lined with fire bricks. CaCI2 is added to decrease the fusing temperature of NaCI from 801°C to 600°C which makes the process feasible. The cell is fitted with a graphite anode and a surrounding by iron cathode. The two electrodes are separated by a cylindrical iron gauze. This keeps away the molten sodium which floats to the top of cathode compartment from CI2 formed at anode. Na-metal collects in the inverted trough ‘T’ placed over the cathode, rises up the pipe ‘P’ and is tapped off through iron vessel ‘V’.

Reactions of The Cell

Reactions of The Cell

Reactions of The Cell

vii) (a) Write I.U.P.A.C. names of the following:
• NH.• [ Cr (SCN)4 (NH3) 2]
Ans: Amonium Tetra thio cyanato diamme chromate (III)
• Na3 [ Fe (CN)s NO]
Ans: Sodium Nitro so penta cyanato Ferrate (III)
vii) (b) Write the chemical formulae of the following:
• Tineal
Ans: Na2i3407. 10H20
• lead sesquioxide
Ans: Pb304
• Stibnite
Ans: Sb2S3
• Carnallite
Ans: MgCI2. KCI. 6H20
viii) How is Soda Ash manufactured by Ammonia Solvay process?
Ans: See on Page # 348.

ORGANIC CHEMISTRY

ix) Describe the natural sources of organic compounds.
Natural sources of organic compound: Following are the three main sources of organic compound other than plants and animals.
1. Coal
2. Natural gas
3. Petroleum

1. Coal: Coal is the decay product of plant which were buried millions of year ago. It is the source of hundreds of important organic compounds. It is found under the surface of earth at different depths. The main constituent of coal is carbon with some percentages of hydrogen’s, oxygen, nitrogen and sulphur. Anthracite coal, Bituminous coal, lignite and peat are some of its type.
Destructive Distillation of Coal: Following are the three main fractions of coal when it is subjected to destructive distillation.
1. Coke: A solid material which is pure carbon and used as reducing agent in industries.
2. Coal Gas: It IS a gaseous product and used as fuel.
3. Coal tar: It is a viscous’ liquid and source of hundreds organic compound.
2. Natural Gas: Natural gas is also one of the important sources of simple organic compounds especially like methane. Methane is about 85% or more of Natural gas. Sui gas contain 94.6% methane it is mainly used as fuel.

Composition of Sui Gas

Composition of Sui Gas

3. Petroleum: The word petroleum comes from the latin petra (rock)
and oleum (oil). It is a viscous liquid mixture of various components. It contains alkanes, alkenes, cyclo-alkane & aromatic hydro carbons. It is also called crude oil.
The main fractions of petroelum are:
1. Natural gas,
2. Gasoline,
3. Kerosene oil
4. Diesel Oil,
5. Lubricating oil and waxes
6. Asphalt.
x) (a) Define the following, giving examples: \
Isomers
The organic compounds having same molecule formula but different structure formulae are called isomers:
Exmp: (i) CH3 – CH2 – OH Ethyl Alcohol
(ii) CH3 – 0 – CH3 Dimethyl Ether
Both have molecule formula C2H60. The are Isomers .
Polymers ,
Numbers of small molecule having less molecular masses unit together to forms large molecule having high molecule mass called polymers, that phenomenon called polymerlzatlon.
Example ‘of Polymers: ‘
Polyethene (a polymers of ethene)
P.v. C (a polymers of vinyl chloride)
x) (b) ‘Acetylene shows acidic properties.’ Give two reactions to justify this statement.
(1) Reaction with Na metal. •
CH == CH + 2Na ~ NaC == CNa + 2H
(2) Reaction with Heavy metal.
I\’H CH =’ CH + AgN03 1) AgC == CAg + 2HNOJ
xi) (a) Which alkane is obtained by the reaction of metallic Sodium with the following compounds?

Bromo-propane

Bromo-propane

Question Answer

Question Answer

formula

formula

An Oxime from Formaldehyde

An Oxime from Formaldehyde

xv) (a) Give the biological importance of Carbohydrates.
Biologica’ importance of carbohydrates;
I. Ribose and deoxyribose which are aldopentoses, play an important part in human metabolism. They are found in nucleus of cells as RNA & DNA and are heriditory carrier.
2. Slow combustion of glucose in cell, provides energy necessary for our body functions.
3. Body stores part of glucose for rainy days in form of glycogen. In case of emergency glycogen hydrolyze to glucose, thus supply necessary energy.
4. Animal use cellulose of grass, plant, bark as their food.

xv) (b) Explain saponification of oils and fats with the help of chemical equation. Write the names of the products formed.
Hydrolysis of oils or fats with strong alkali such as NaOH. to produce glycerol and soap which is a sodium salt of fatty acid

formula

formula

Saponification: Hydrolysis of oils and fats on boiling with a sol.of NaOH or KOH to form sodium or potassium salt of long fatty acid along with glycerol, is called saponification.
xvi) (a) Give two reactions in which Benzene ring is not retained

formula

formula

SECTION ‘C’ (DETAILED QUESTIONS ANSWER)

3.a) What is Metallurgy? Explain the extraction of 99.99% pure Aluminium from Bauxite ore containing silica as impurity.
Ans: See on Page # 331.

4.a) Explain the manufacture of stable oxyacid of Nitrogen by Ostwald’s method. Write balanced equations for the reaction of HN03 with Cu and C.
Ans: See on Page # 334.

4.b) Write notes on any TWO of the following:
Paints
A paint is usually composed of three components.
1. A binder = Hardens & form a continuous film.
2. A pigment = Supply desire color.
3. A volatile solvent = It evaporates.
In oil-based paints, linseed oil is often used as a binder. The solvent is usually turpentine, a mixture of hydrocarbons obtained from pine trees. The pigment may be .titanium dioxide, carbon black, chrome yellow, oxides of iron or organic dyes of various colors.
Plastic
The macro molecules which are formed by the polymerization of simple molecules are called plastics. Bakelite is a polymer of phenol and form aldehyde

formula

formula

It is used to meke. Buttons, switches, electrical boards, cameras, radio and telephonic components.
Photography
Photography is an art of producing picture of illuminating object on chemically prepared surface.
A photo graphic plate or film consists of an emulsion of silver bromide & silver iodide suspended in gelatin coated to a cellulose acetate sheet.
Silver bromide is light sensitive & undergo .photo chemical decomposition.
On exposure to light some of the grains of silver bromide in the photographic plate undergo reduction to metallic silver. This film can be developed by organic reducing agents such as metal hydroquinone or prygallol, called developers. This reduces the sensitized silver bromid to Ag-metal. By this method the developed film reproduces the pattem of light that exposed it. This film is called the negative because -it is blackened with metallic silver where the light in the original image was most intense.

The negative film is then fixed by immersing it in the fixing bath containing the solution of sodium thiosulphate called hypo.

formula

formula

A positive print can be made by exposing photographic paper containing a coat of silver-bromide and silver iodide emulsion, to light that passes through the super imposed negative print. The exposed paper is finally developed & fixed in a similar manner.

lead pigments
Ans: See on Page # 332.

Boric acid
Ans: Preparation:
From Borax: Boric acid is prepared by the action of H2S04 on hot sol. Of borax. The resulting sol. On cooling give crystals of boric acid

formula

formula

2. From Boron Nitride: Boric acid is also obtained by the action of boron nitride on super heated water

formula

formula

Structure: H3B03 forms white needle like crystals in which B(OH)J units are linked together by H-bonding to form infinite layers. These layers lie 3.18° A apart from one another & held together by vender waal’s forces, due to this reason they glide over one another.
Properties:
1. Crystals of H3B03 are white, soft & silky.
2. It is greasy to feel. ,.
3. It is sparingly soluble in coM water buf readily soluble in hot water.
4. It is mono basic eak acid. .
5. It is mild antlseplic.
6. On heating it produces different

formula

formula

4.c) What is Corrosion? Write its causes. Give different methods for the prevention of metals from corrosion.
Ans: See on Page # 332.

ORGANIC CHEMISTRY

5.a) Explain the molecular orbital treatment of Benzene. Also dl _·v the resonance structures of Benzene.
Ans: See on Page # 336

Question Answer

Question Answer

5.c) Draw the molecular structure of Ethene and discuss its orbital structure.
Ans: See on Page # 328

6.a) What are Vitamins? How are they classified? Write their names and sources. Also name the diseases caused by their deficiency.
Vitamins
: Vitamins are essential accessory of food factors which are necessary for complete normal metabolism of tne energy yielding constitutes of the diet and are must for normal body growth & development.
Classification of Vitamins: Vitamins are generally classified into two groups. on the baSIS of their solubility
1. Fat Soluble Vitamins: It includes Vitamin – A. D. E and K.
2. Water Soluble Vitamins: It includes vitamin B complex & vitamin

Fat Soluble Vitamins:
1- Vitamin A: (Retinol)
Deficiency:
• Dlyness of cornea.
• Softness of Cornea
• Night blindness
• Lowers the resistance against infections
Source: Milk, fats of animals, egg, liver kidney, fruits, green leaves, tomatoes etc.
2- Vitamin: (Antirachitic)
Source: Cold liver oil, egg, butter, cheese, milk etc.
Deficiency:
• Rickets in children
• Osteoporosis in adults
• Tooth decay
3- Vitamins E: (Tocopherol)
Source: Milk, Wheat grains, green vegetables, oil, egg yolk, etc.
Deficiency:
• Fragility of red blood cells.
• Decline in respiration
4- Vitamin K: (menaclione I Antihaemorrhage)
Source: Alfa alfa, fish, spinach, cauli flower, cabbage
Deficiency:
• It increase the blood clothing time.
Water Soluble Vitamins:
1- Vitamin B1: (Thilamine)
Source: Yeast, Wheat, green peas, kidney, liver.
Deficiency:
• Heat failure
• Mental depression
• Loss of weight
• Beri-Beri
• Loss of appetite and constipation
2- Vitamin B2: (Riboflauin):
Source: Liver, egg, milk, cheese etc.
Deficiency:
• Growth retarded •
• Cracks and fissuees on skin, especially at comers of the mouth.
• Tendency to increase cataract formation.
3. Nicotine Acid or B6: (Niacin):
Source: Wheat, milk, egg, liver, kidney, yeast, peanuts, etc.
Deficiency:
• G.I.T disturbance (dirrhoea)
• Nervous system .
4. Vitamin ‘C’ (Ascorbic acid)

Question Answer

Question Answer

Question Answer

Question Answer

 

Posted on December 31, 2015 in 2nd Year 2013 Karachi Board Past Papers

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