Chemistry Solved Past Paper 2nd year 2014 Karachi Board

SECTION ‘A’ (MULTIPLE QUESTIONS ANSWER)

1. Choose the correct answer from the given options

i) Fertilizer maintains the range of pH of soil at:
7.0-8.0
• 4.0-6.0
• 1.2-4.2 .
• 12.0-14.0

ii) The first-seven groups of the periodic table are divided into sub-groups ‘A’ consisting of:
• Transition elements
Representative elements
• Metallic elements
• Complex elements

iii) Interstitial hydrides are also named as:
Metallic hydrides
• Covalent hydrides
• Borderline hydrides
• Ionic hydrides

iv) Saponification results in the formation of:
• Glass
• Polymer
• Fertilizer
Soap

v) The boiling point range 40°_ 200°C is for this fraction of petroleum:
• Wax
Gasoline
• Heavy oil
• Jet fuel

vi) The ratio of electron, proton and neutron in Protium is:
(1:1:0)
• (1:1:1)
• (1:2:1)
• (1:1:2)

vii) EDTA is:
• Bidentate ligand
• Monodentate ligand
• Chelate
Multidentate liaand

viii) Another name for Methane is:
• Mustard gas
• Oil gas
• Coal gas
Marsh gas

ix) An example of electron deficient hydrides is:
BH3
• NaBH4
• NaH
• CH4

x) Chemical name for Fruit’suga( is:·
• Sucrose
• Glucose
• Lactose
Fructose

xiv) The chemical formula A1203.3H:zOstands for:
• Diaspore
• Corundum
• Bauxite
• Gibbisite

xv) This imparts red co/our to glass:
• Cr2Q3
• CuO
•CoO
ZnO

xvi) The formula of Caproic acid is:
• CH3.(CH2kCOOH
• CH3.(CH2hCOOH
• CH3.CH2.COOH
CH3.(CH2l4.COOH

xvii) The number of carbon atoms in a Monosaccharide is:
• 3-10
• 2-8
• 3-9
• 4-9

SECTION ‘B’ (SHORT QUESTIONS ANSWER)

INORGANIC CHEMISTRY

2.i) What are the demerits of Mendeleev’s periodic classification? How was it modified?
Mendeleev’s Period Classification:
Demerits:
Mendeleev’s left certain gaps in his periodic table for the elements to be discovered.
It was observed that at certain places, an element of higher atomic masses cobalt (CO = 58.93) has been placed before an element of lower at mass (Ni = 58.71)
Modification: Mendeleev’s period table was modified to modern periodic law.
“The properties of the elements are the periodic function of their atomic numbers & not the atomic weight.”

ii) Give scientific reasons for any four:
NH3 and H20 act as ligands but NH ~ and H30· do not.
This is because NH3 and H20 have lore pair of electrons. Due to presence of lone pair they act as legand while lone pair is occupied by Hydrogen atom in NH; & H30+.
Graphite conducts electricity, whereas diamond does not.
In diamond each C-atom utilizes its four unpaired electrons in the formation of four covalent bonds. These bonding electrons pair are localized between specific pair of C-atom. Due to this diamond is bad conductor of electricity. While in graphite one of the four electron of each c-atom form delocalized n-bond which spread uniformly over all Catoms.
Due to which it conducts electricity.
B2O3 is acidic while AI203 is amphoteric.
B2O3 When dissolve in water produce H+ ions while when AI203 dissolved ·in water produce both H+& OW ~es of ions therefore it is amphoterie.

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Alkaline earth metal ions are more strongly hydrated than alkali metal ions.
Alkaline earth metals posses +2 charge i.e they form di-ion which results in stronger attraction. Thats why they form move strong hydrated ions,

Most of the transition elements and their compounds are paramagnetic.
This is blc of the presence of unpaired electron spin in the ions and atoms of the elements

iii) Describe the manufacture of Chlorine gas by Castner-Kellner cell.
Castner – Kellner Cell: Construction of the Cell: This cell has a cathode consisting of layer of mercury at the bottom of cell which flows from right to left. Saturated solution of NaCI also flows in the same direction

The anode rods of graphite dip into the solution of NaCl On Electrolysis following reaction taken place

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Question Answer

Question Answer

vii) (a) How does Crystal Field Theory explain the colour of complex ions?
According to Crystal field theory. The bonding between ligands and metal ion is electrostatic. The ligand surrounds the metal ion create an electrostatic field around d-orbitals. This field split 5 – d – orbital into two sets with different energies,
(i) higher energy pair ego
(ii) lower energy trio fig

formula

formula

Thus, by absorbing visible light, electron jumps from lower energy level to higher energy. In doing this some of the components of while ligftt is removed the reflect the remaining light. Hence show different colours.

vii) (b) Write the formulae for the following:
* Alunite
* Hypo
* Magnesite
* Fluorspar

Question Answer

Question Answer

ORGANIC CHEMISTRY

lx) (a) Draw and explain the orbital structure of Ethyne.
Structure: Each carbon atom in ethyne is attached to one Hatom by a single covalent bond (cr-bond) and to another c-atom by a triple bond. .
Thus each c-atom uses Sp 1 hybridized orbitals and two unhybridizing 2P – orbitals (Py and P.) to form its Pi-bond.

daigram

daigram

ix) (b) What is Rancidification? Mention its causes.
Rancidification: When oils and fats are left exposed to warm, moist air for a long time, they give off offensive odour and become  fftaste.
This process is called Rancidification.
Causes:
It is caused due to hydrolysis of ester linkage to give original fatty acid of sour taste.
Oxidation at double bond forming volatile aldehyde of bad odour.

x) Define the following:
Homologous series
A series of compound in which various members have similar structure features but different from each other by an integral member of CH2 group, is called homologous series.
Cracking
Splitting of the larger molecules of the less volatile fractions into smaller molecules of greater voltility by subjected them to higher temp & pressure is called cracking.

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Refining of petroleum
When crude oil is subjected to fractional distillation several groups of products are obtained. This is known as refining of petroleum.
Carbohydrate
Carbohydrates are polyhydric aldehydes or ketones i.e. (trley are either aldehydes or ketones) having many – OH groups) and other substances, which on hydrolysis produce such compounds.

Question Answer

Question Answer

xiii) (a) What are Monohydric alcohols? Ht!7W are they classified?
Monohydric alcohols are classified as primary, secondary and tertary depending on whether the -OH group is attached to primary, secondary or tertiary C-atom

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xiii) (b) How is wood spirit manufactured from Water gas?
Wood spirit (methanol) is prepared by water gas by passing ove! heated catalyst (mixture of ZnO & Cr203) in the pressure of 200 atm.

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xiv) What sYrlthetic fibre? Explain Nylon and Polyester.
Synthetic fibre: A type of fiber manufactured from cellulose such as cellulose acetate, nitro cellulose is called Rayon. This is synthetic fiber.
Nylon: Nylon is made of diamines and di basic acids which can be synthesized from common raw material i.e coal, water, air. Nylon is a type of polymer in which amide linkage holds the cham together.
Polyester: Terylene is a polyester fabric which is formed from many
ester molecules. The monomers for the manufacture of terylene are ethylene glycol and terephthalic acid.

xv) (a) How is Benzene prepared commercially from petroleum?

Answer

Answer

Answer

Answer

xv) Differentiate between the following:

Saturated and Unsaturated hydrocarbon

Saturated and Unsaturated hydrocarbon

Reducing and Nori-reducing sugar

Reducing and Nori-reducing sugar

SECTION ‘C’ (DETAILED QUESTIONS ANSWER)

INORGANIC CHEMISTRY

3.a) How is Soda ash manufactured by Ammonia Solvay process?
Ammonia Solvay Process:
Introduction: Sodium carbonate is manufactured on large scale by Ammonia solvay process.
Raw Materials:
Brine (20% sol. Of NaCI)
CaC03 (a source for C02)
NH3 gas (Recoved from the process)
The process involves three important steps and its flow-sheets diagram.
The process involves three main steps.
1. Ammoniation of Brine: In this step saturated solution of brine is allowed to flow down in an ammoniating tower. The tower consist of mushroom-shaped baffles at short intervals which controls the flow of brine and ensure proper saturation.

2. Carbonation of Ammoniated Brine: In this step ammoniated brine is allowed to tickle down a carbonating tower, called solvay tower and meets an upward current of C02 obtained by heating CaC03. The CO2 and NH3 react to give NH/ and HC03- ions.

formula

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Ammonium bicarbonate reacts witti brine to form sodium bicarbonate.

Ammonia-Solvay process

Ammonia-Solvay process

Conversion of Sodium Bicarbonate into Sodium Carbonate:
NaHC03 is heated to give anhydrous sodium carbonate. (Soda ash).

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3.b) Describe the extraction of pure Copper from roasted pyrite
ore.
Matte: The molten mixture of CU2S and Fes is called matte. Extraction Of Cu: The liquid copper matte containing CU2S with some unreacted Fes and Silica is oxidized in. a Bessemer converter by blowing air. FeS is oxidized to FeO and S02. FeO reacted with sand to give ferrous silicate and the blast of air .ccmyerts CU2S partly into CU20 which reacts with remaining CU2S to give metallic copper in molten state..

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The Cu thus produced is called blister Cu which is 99% pure.
Blister Cu Refining: Blister Cu is refined by electrolysis, in which blocks of blister Cu are used .as anode and thin sheets of pure Cu as cathode. The cathode’ plates or sheets are coated with graphite in order to remove depositing Cu easily. The electrolyte is CUS04, acidified’with ·H2S04. The current of 1.3V is used for -electrolysls which helps to deposit Cu only on the cathode leaving impurities which are solusle and fall to the bottom of the cell as an anode mud. The chemical reactions occur are given below:

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4.a) Explain why Hydrogen is misfit in group fA and VilA of the periodic table.
Position of Hydrogen:
Misift in I A:
It is because:
Hydrogen is gas, while IA elements are non-metals.
It does not loose it valence electron like IA elements.
Misfit in VilA:
Unlike CI-, W is unstable to exist in water since H2 is readly formed. E.N of Hydrogen is much less than halogens.

4.b) Describe the manufacture of Sulphuric acid by Contact process. Draw the flow diagram.

“Contact Process”
Introduction: The present day method which produces pure H2S04  is the contact method.
The step of the procedure are as follow:
1. Formation of 502: S02 is produced by buming sulphur or iron pyrite in pyrite bumers

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Question Answer

Question Answer

Atomic Hydrogen is more reactive than molecular hydrogen because it is very unstable.
– It is used in obtaining atomic hydrogen torch to attain a temperature of 4000 – 50000C which is used in welding.

Blue vitrlol
Formula; CuS04.5H20
Chemical Name: Copper Sulphate:
Preparation:
Copper sulphate is prepared by reaction of metallic Cu with dilute H2S04 in the presence of air. .
2Cu + 2H2S04 + 02 —7 2CUS04 + 2H20
It can also be prepared by dissolving CuO or CUC03 in dilute H2S04.
CuO + 2H2S04 —7 CUS04 + H20
CUC03 + H2S04 —7 CUS04 + C02 + H20
CUS04 crystals are blue in color which on heating loose all its water of crystallization & turn colourless.
CuS045H20 230″C) CUS04 + 5H20

Blue White
CUS04 is very soluble in water.
It is insolube in alcohol.
It is used in Cu-plating, in electric cells, in making green pigments, as a modant in dying.

ORGANIC CHEMISTRY

5.a) Describe Kek\Jle structure of Benzene. Write the objection against it. How was this objection removed by Kekule?
Kekule’s Structure: Kekule” Structure of Benzene Kekule tn 1865 proposed a ring structure for benzene with alternate carbon- carbon double bouds.

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formula

The structure of benzene is equally represented by structure I & II. The double bond is not fixed & all the carbon atoms have double bod half of the time arid single bond for the other half
Objection & its defence: The objection to kekule formula was that it would give two disubstituted ortho- products where as in actual practice only one was isolated.

formula

formula

In I, X & Yare on carbon containing single bond while in II, X & Yare
present on carbon containing double bond. To explain why only one
product is obtained kekule formulated a theory that carbon atoms in
benzene were in state of viberation & due to this viberation each c–c atom have single bond half of the time and double bond the o,ther half

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formula

5.b) What are Elimination Reactions? Write Bimolecular Elimination Reaction with its mechanism.
Elimination Reactions: Those reactions which involves the removal of two atoms or groups from adjacert c-atom of the molecule to form a multiple bond, is called elimination reaction.
Bi-molecular Elimination: Elimination in which alkyl halide & Nucleophile involve in rate determining step is called bi-rnoleculae
elimination. or E2. Reaction of primary alkyl halide are generally E2 reaction. Which occur through transition state:
Mechanism:

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It is one step reaction
Rate of Reaction = K[R – CH2 – CH2 – X] [OHl
Where K is constant.

5.c) Give equations for the following reactions .
Phenol with dilute HN03.

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6.a) What is Fermentation? How is Ethyl alcohol manufactured by the fermentation of:
* Starch * Molasses
Fermentation: It is a process in which sugars such as gl cose.
fructose are converted into cellular energy also produce alcohol & CO: as waste formation of Ethyl Alcohol.
From Starch: To prepare alcohol from starch, the grain is cooked to
form a pulp and then to this is added malt. The enzyme present in malt hydrolyze starch to sugar mallose. Melto~e convert into glucose by yeast & further to ethanol.

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Fermantation of Molasses: The thick brown colour syrup left after isoloation of crystalline sugar cane is treated with yeast, which contain enzymes sucrase, which converts sugar to glucose and fructose and further to ethanol.

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6.b) Why does Benzene give Electrophilic Substitution Reactions? Explain the mechanism of Friedel-Craft’s Acylation.
Electrophylic Substitution Reaction in Benzene: There is a cloud of electron above and below the plane of benzene molecule. This cloud of electron are responsible for electrophilic substitution reaction.
Acylation by Fridel craft Reaction: To introduce acyl group (R – C = 0) in the benzene ring is achieved with the help of lewis acid such as AJCb. The reaction is konwn as fridet craft reaction.
‘Reaction: In this Aceyl halide reacts with benzene in the presence of lewis acid.

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OR Write notes on any two of the following:
Glass
Glass is one of the mot important artificial silicates. It is the mixture of sodium silicate & calcium sicate.
Formation: I is produced by heating sand, soda. sodium sulphate and lime stone in a furnace a 1400°C

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Glass is attached by HF. This acid is used to ma e designs on 9 ass. This process is called etching.

Detergent
Soapless deansing. agents are called de ergents. They are comp ex organic salts with long chain molecules. Structure: All detergents ha e same basic structure. They are made of two paris:

HydrophobIC
Hydrophilic

Hydrophobic part is the fong hjdrocifbon chain with covalent bonds being non-po r in na e it attracts oi & grease.
Hydrophylic part is small ionic ~roup Ii e sulphonate

Amino acids
Definition: Amino acids are org ic compounds containing two functional fjroups, an amino group and carboxyl group.

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Essential Amino cids: These are the amino acids y:hich ca be synthesized by one’s body but they are essential for growth” There defency results in many diseases”
Classificaticm: These are cbssified as:
Neutral Am”no acids”
Acidic Am”no acids”
Basic Amino acids.

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Posted on January 1, 2016 in 2nd Year 2014 Karachi Board Past Papers

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