Chemistry Solved Past Paper 2nd year 2015 Karachi Board

SECTION ‘A’ (MULTIPLE QUESTIONS ANSWER)

solved MCQs chemistry 2015 2nd year

solved MCQs chemistry 2015 2nd year

solved MCQs chemistry 2015 2nd year

solved MCQs chemistry 2015 2nd year

SECTION ‘B’ (SHORT QUESTIONS ANSWER)

INORGANIC CHEMISTRY

Question Answer

Question Answer

ii) Give scientific reasons for the following:
” Hydrogen exhibits +1 and -1 oxidation states in its compounds.
Due to half filled valence orbital hydrogen exhibt +1 & -1 oxidation states by either gain one electron to complete its orbit forming H- or by loosing its valence electron forming H+.

Alkali metals are powerful reducing agents.
Alkali metals have one electron in their valence shell. They readily loose one electron to attain stable electronic configuration and hence by loosing electron they oxidize themselves and reduce other compounds.

So3 is dissolved in H2S04 but not in water.
Ans: In the preparation of sulphuric acid. S03 is first dissolved in H2S0< to form oleum & not in water. but the reaction with water will be uncontrollable & it creates a fog of sulphuric acid.

Question Answer

Question Answer

5. Polmeric hydrides
6. Borderline hydrides

Ionic hydride:
Preparation: This type of hydrides are formed by the metals of group IA & group IIA except Be & Mg

formula

formula

Properties:
They are odourless
Non-volatile
Having high melting points

vii) How is Blister copper obtained from matte?
Copper is mostly extracted from its sulphide ore which contains. about 6% of Cu. The sulphide ore is first roasted. The roasted material is than mixed with sand to remove iron. The liquid copper matte containing CU2S with unreacted FeS & Silica is oxidized in a Bessemer converter by blowing air. FeS is oxidized to FeO & S02 and the blast of air converts CU2S partly CU20 which react with remaining CU2S to give metallic copper

formula

formula

viii) Write the names and formulae of oxyacids of Boron and give the effects of change in temperature on them.
Oxyacids of Boron
Names Formulae
Netaboric acid HB02
Pyroboric acid H2B2O7

formula

formula

ORGANIC CHEMISTRY

IX) Define the following with examples:
Octane number
Octane number of a gasoline is a measure of its ability to resist knocking as it burns in combustion.
Catenation
It is the linkage of atoms of the same elements into longer chains. It occurs mostly in carbon atoms.

H3C – CH2 – CH2 – CH2 – CH3 Pentane

• Functional group
The properties of an organic compound depends upon the presence of an atom or group of atom that is substituted in the chain of C-atoms in place of H-atom which is termed as functional group.
Alcohol = R – OH ether = R – 0 – R’

Metamerism
It is a type of isomerism which is exhibited by the compound having same functional group but different alkyl group attached to same multivalent atom.
e.g: CH3 – CH2 – 0 – CH2 – CH3
CH3 – CH2 – CH2 – 0 – CH3

x) Draw and explain the orbital structure of Ethene.
Ethene C2H4

hybridized

hybridized

It the molecule of C2H4. each carbon is Sp2 Hybridized having an angle 1200 along with three Sp2 hybrid orbitals. One pz orbit of each carbon remains unhybridized which is perpendicular to the plane

un hybridized

un hybridized

Each carbon utilizes its one Sp2 hybrid orbital linearly forming (8) bond. Remaining Sp2 hybrid orbitals of each carbon overlap linearly with 1S orbital of hydrogen as a result four sigma (8) bond are formed. Each pzunhybridized orbital carbon is parallel to each other. So they form a pi (n) bond.
In the molecule of Ethene there are five sigma (8) and one pi (n) bond

xi) Write the Nitration reaction in Benzene along with its mechanism.
• Niration in Benzene:

formula

formula

Mechanism

Mechanism

xii) Write the role of Amino acids in the human body.
Role of Amino Acid in Human Body:
1. Amino acids are essential for growth of infants.
2. Transmission of impulses in nervous system.

xiii) What are Organometallic compounds? Prepare the following from anyone organometallic compound.
* Ethane * Ethyl alcohol * Vinegar
Compounds that contain a metal-carbon bond, R-M are known as -orqanornetallic compounds.
* Ethane from organometallic compounds: Ethyl Magnesium chloride reacts with methyl alcohol which gives ethane

formula

formula

Vinegar from organometallic compounds. On reaction of C02 with grignard’s reagent, it produce acetic acid” .. i.e vinegar

formula

formula

formula

formula

SECTION ‘C’ (DETAILED QUESTIONS ANSWER)

3.a) What is meant by Metallurgy. Describe the extraction of 99.99% pure Aluminium from Bauxite ore containing Si02 and Fe203 as impurities.
Metallurgy: Metals are found in universe as combined form these combined forms of metals are called minerals. The process by which metals can be extracted from their ores is known as metallurgy.
Extraction of Aluminum:
Aluminium is extracted from Bauxite ore. The meallurgy of aluminium involves followins teps.
i. Purification of Bauxite: Bauxite usually contains impurities like Fe203,Si02 which makes aluminium briltle. The bauxite may be purified by following ‘method.
Serpek’s Process: This method is used for the purification of bauxite
containing Si02. In this process the powdered bauxite is mixed with carbon (coke) and hetaed up to 1800°C in the presence of nitrogen when AIN is formed

formula

formula

Aluminium nitride on hydrolysis with hot water produces precipitates of AI(OH)J and NH3,

formula

formula

Electrolysis of Pure ALumina: Pure alumina obtained from the purification of bauxite. It is then dissolved in used cryolite (NaJAIF6) and fluorspar (CaF2) and electrolized in an electric’furance.

Cryolite lowers the melting point of Alumina from 250°C to 950°C and also makes it a good conductor where as flourspar (CaF2) increase the fluidity of the electrolyte.
The electrolysis is carried out in a steel tank lined with carbon (Graphite) from inside this graphite linning serves as cathode. The anode consists of graphite rods hanging in the molten mass when the electric current is passed through the molten electrolyte the resistance of electrolyte gives sufficient heat to keep the mass in molten state (around 950°C)

During electrolysis aluminium is liberated at the cathode and being in liquid state it sinks to the bolton and forms a pool from when it is taken and periodically through taping hole. At the same type oxygen is liberated at anode which react with graphite rods and producing. C02 and CO. This destroys carbon rods which are replaced without stopping the electrolysis. Aluminium thus obtained is 99.99% pure.

3.b} Write note on any One of the following:
Lead Pigments
Lead form various types of pigments which are used to give the proper color to paints. Some of them are given below:
i) White lead pigment
ii) Red lead pigment
iii) Chromo yellow pigment
iv) Chromo red pigment
v) Turner’s yellow pigment.

1. White Lead Pigment: It is basic lead carbonate and has approxi mately composition as
[2PbC03.Pb(OH)2] or Pb3(OH)2. (C03)2.
It is prepared by passing C02 into the suspension of lead oxide in water containing little amount of lead acetate.
2Pb02+2C02+2H20+Pb(CH3COOh -7
[PbC03.Pb(OH)2)+CH3COOH +02.
It is used as while pigment for paints.

2. Red Lead Pigment (sandhur): It is called triplumbic tetra oxide or lead sesqui oxide. Its composition is Pb304 or (2PbO.Pb02).
It is prepared by heatinq lead monoxide in excess of air at 450°C.
6PbO + 02 450°C) 2Pb304.
Red lead
It is used as red colored pigment in paints.

3. Chrome Yellow Pigment: It is lead chromate with composition PbCr04.
It is prepared by adding the solution of potassium chromate to the solution of lead nitrate, then fine yellow ppt of lead chromate are formed.

formula

formula

It is yellow colored pigment insoluble in water but soluble in nitric acid and caustic alkalis.
4. Chrome Red Pigment: It is basic lead chromate and its composition

formula

formula

Corrosion and its preventions
Definition:
“A harmful and an undesirable reaction of a metal material as a  result of exposure to moisture or any chemical agent is called corrosion.” !
Almost all metals except noble metals like Ag, Au & Pt show great tendency to corrode with different rates when exposed to water or atmosphere. Na & K- metals tarnish immediately (In exposure to air, Ca corrode quickly, iron corrodes slowly and tin, lead & Cu corrode very slowly.
Prevention: It has been learnt through experiments that due to corrosion 1/Sth of the iron used is lost annually. Since iron steel are widely used metals, number of various methods have been used to prevent corrosion.
i) Metal Coating: The iron or steel can be protected from corrosion by coating with another metal as in galvanized iron i.e. coating with zinc, tin etc.
ii) Electroplating: Noble or bare metals are used for electroplating on
any desire metal.
iii) Alloying of metals: One of the most important way of protection of
a metal from corrosion is by mixing of it with another metal i.e. alloy formation.
iv) Coating with Non-Metallic Meterials: Metals can be protected from corrosion by using various’ kinds of non-metallic materials such as paints, oils, grease etc.

Lunar Caustic
Preparation: Silver nitrate or lunar caustic is prepared by – dissolving Ag-metal in dil HNO;s.-E)n OI”fStallization, the long crystals or sticks are formed.
3Ag + 4HN03 -t 3AgN03 + NO +H20

Properties:
1. AgN03 is readily soluble in water.
2. It is also soluble in organic solvents such as ethyl alcohol, pyridine etc.
3. It decomposes at 450°C.

formula

formula

4.a) Describe the manufacture of Nitric acid by Ostwald’s process. Draw the flow diagram. Write balanced equations for the reaction of dilute and very dilute Nitric acid with Zn.
Manufacture of Nitric Acid (HN03) Ostwald’s Process: HN03 is prepared commercially by the oxidation of ammonia by Ostwald’s process. In this method NH3 is oxidized to NO in the presence of catalyst at 600°C NO than oxidize to N02 which is dissolved in H20 to form HN03.
The details of each step is given below:
1. Oxidation of NH3: One part by volume of NH3 is mixed with 8 parts by volume of air, the mixture is allowed to enter the converter which contains pt gauge heated to a temperature of 600°C in the beginning the temperature is then maintained due to exothermic reaction of oxidation of NH3. About 95% of NH3 is oxidized to NO. The gases from the converter are led by iron pipes which passes through a boiler. Stem is produced by the absorption of heat from the gases and the temperature is lowered to 150°C.

2. Oxidation of NO to N02: NO’ and air enters the oxidation chamber where the temperature is further lowered to 50°C and NO is oxidized to N02

daigram

daigram

3. Formation of HN03: N02 gas from the oxidation chamber is allowed to enter the absorption tower packed with acid proof stones. The gas is absorbed by water sprayed from the top of the tower. It is recycled to absorb more & more N02 gas till maximum saturation is obtained.
Reaction of HN03 with Cu & C:

formula

formula

4.b) Describe the extraction of Sodium from molten Sodium chloride.
Extraction of Sodium from NaCI: Na is extracted from molten NaCI by Down’s process.
Down’s Process: In this process molten NaCI involves the reduction of Na’ ions at cathode. In this method mixture of NaCI & CaCI2 is electrolysed in an iron cell. CaCI2 is added to decrease the fusion
temperature of NaCI to 600°C & a surrounding iron cathode. The two electrodes are separated by iron gauze. The sodium metal collects in the inverted through placed qver the cathode.

formula

formula

4.c) How is Chlorine manufactured by Nelson Cell? Draw. its diagram. Give equation for the Auto-oxidation reduction reaction of Chlorine.
Nelson’s Cell: This cell consist of U-shaped perforated steel vessel which acts as cathode & carbon rod as anode. This u·tube is separated from anode by asbestos layer deposited on the inner wall of u-tube.
This u-tube is filled by aqueous solution of NaCI. On passing electric Current, CI2 is obtained at anode
(i) Ionization
NaCI ==e= Na+ + CI-
(ii) Reaction at Anode:
2CI- ~ Cla + 2e-

Manufacture of Chlorine

Manufacture of Chlorine

Auto Oxidation Reaction of Clz: Chlorine reacts with sater to form hydrochloric acid & hypochlorous acid in this reaction CI2 oxidize as well reduces. Hence it is known as sef oxidation reduction reaction.
CI2 + H20  HCI + HOCI

ORGANIC CHEMISTRY

5.a) Explain the molecular orbital treatment of Benzene. Also draw the resonance structure of Benzene.
Molecular Orbital Treatment of Benzene: Benzene molecule is a regular that hexagon, with all six H-atoms lying in plane of the ring &
that the bond angles of the C.- C atoms in the rin~ & C – C – H atoms are all 120°. Which shows that each C-atom is Sp hybridized. The Sp2 orbital of adjacent C-atom overlap with each other linearly & form sigma bound.

The third electron of each C-atom forms another sigma bond with is
orbital of H-atom (Sp2_S). So there are 12 sigma bonds. Six between C – C six between C – H. The fought electron of 2pz1 remain with C-atom in the form by lobe. The 2Pz 1 of the two adjacent C-atoms are shared forming 11: – orbital. These TI – orbitals are parallel to each other. There are six 2Pz 1 electrons on each carbon atom which remain perpendicular to the plane of the ring & parallel to each other.

formula

formula

Aromaticity: The property of special class of hydrocarbon containing
benzene ring having pleasant small is Armotiacity. The molecular orbital representation of benzene is useful for the understanding of high stability of benzene ring. The telectron above & below the ‘surface of ring are responsible for substitution reaction of benzene.
In these type of reactions an electrophilic attacks the 1t-system of benzene to yield delocalized carbocation known as arenium ion. This breaks the cyclic system of t: electrons, blc when arenium ion is formed, one carbon become Sp3 hyberdized. This causes instability and to overcome this instability thearenium ion loses a proton from the carbon that bears the electrophile. The loss of proton results in regeneration of 1t-system which restores the stability of the ring.
Draw Resonance Structure of Benzene:

formula

formula

5.b) Define Polymerization. How many types of Polymerizations are there? Give the preparation of the following:
* PVC * Bakelite
Polymerization: The process in which many small molecules join together to form very large molecule.
Types:
(i) Addition Polymerization
(ii) Condensation Polymerization
Preparation of PVC: molecules of ethylene undergo self combination to produce PVC

formula

formula

formula

formula

6.a) What is Nucleophile? Explain the reaction mechanism of SN1 and SN2 reactions with example.
Nucleophile: Nucleophile is an eleotronegative ion substitutes the halogen atom of the alkyl halide.
SN1 Reaction Mechanism: SN, reaction occurs in two steps in the first step the C – X bond splits reversing to give a positively charged ion and a halide ion.
In the second step the attacking nucleophile reacts with the positively charged ion to give final product

formula

formula

Mechanism of SN2 Reaction: In SN2 reaction, the formation of the carbon Nucleophile bond & the cleavage of C-halogen bond occurs simultaneously. Since the nucleophile enters as halide leave. It atta s the carbon from the side opposite to that form which the halide leaves.

formula

formula

6.b) What is Fertilizer?Give its types. Explain phosphatic fertilizers.
Fertilizers: Fertilize’s are inorganic salts mostly contain eler ents such as nitrogen, phospborous, potassium etc. The make the soil move fertile.
Types: There are two type of fertilizers,
1. Organic fertilizer’
2. Mineral fertllizers
Phosphatic fertilizers:I as super phosphate & triple phosphate.
The raw matenal for these ~ .i1izers is phosphate rock or phos] “rite, [Ca3(P04)2h CaF2.

formula

formula

formula

formula

Posted on January 1, 2016 in 2nd Year 2015 Karachi Board Past Papers

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