Chemistry Solved Past Paper 2nd year 2012 Karachi Board

SECTION ‘A’ (MULTIPLE QUESTIONS ANSWER)

1. Choose the correct answer from the given options:

i) The number of elements in each- lanthanide and actinide series is:
* 2
* 14
* 8
* 32

ii) Water gas is produed by passing steam over red hot coke at:
* 800°C
* 900°C
* 600°C
* 10000C

iii) This metal forms super oxide:
* Li
* Be
* K
* Mg

iv) Tineal is a mineral of:
* AI
* Si
* B
* C

v) Kipp’s apparatus is used to prepare:
* HCI
* CI2
* H2S
* S02

vi) This gas is produced ~y treating ethane with sulphur monochloride:
• Tear gas
• Mustard gas
• Laughing gas
• Marsh gas

vii) This gas is used in welding::
• Methane
* Ethyne
•. Ethane
• Ethene

viii) Grignard’s reagent reacts with ketone to give:
•. 1° – alcohol
* 2G – alcohol
•. 3° – alcohol
•. phenol .

ix) Cholestrol, cholic acid and progesterone are:
* Amino Acids
* Proteins
• Steriods
* Enzymes

x) In Tollen’s test, the end product is:
• White ppt
•. Red ppt
•. Yellow ppt
* Silver mirror

xi) NaOH is named as caustic soda because:
• it is used in soda water
• it corrodes organic tissues
* it reacts with chlorine gas
• it reacts with fats to form soap

xii) Brine is a concentrated aqueous st5lution of:
* sodium carbonate
•. sodium sulphate
* alum
* sodium chloride

xiii) The process of covering Iron sheets by a layer of Zinc is known as:
* Tempering
* Tin plating
•. Galvanizina
•. Annealing

xiv) The functional group present in cresol is:
• phenolic, – OH
• carboxylic, – COOH
• alcoholic, – OH
• aldehydic, – CHO

xv) Milk sugar is also called:
* Glucose
• Fructose
• Lactose
• Sucrose

xvi) Dimethyl ether and Ethyl alcohol are:
• metamers
• functional group isomers
• position isomers
* cis-tans isomers

xvii) This functional group is presenting oil and tats:
•. Carboxylic group
* alcoholic group
* aldehydic group
* ester group

SECTION ‘B’ (SHORT QUESTIONS ANSWER)

INORGANIC CHEMISTRY

2.i) State the Modem periodic law. Explain how it removed the defects of Mendeleev’s System of classification .
Modem Periodic law: This law states that:

The physical and chemical properties of the elements are the penomc function of their atomic numbers n their atomic masses.
(1) The periodic law provides t e logical and scientific ground fer the classification of elements.
(2) This law a so provides justification for correcting the positions Of some wrongly placed elements in e. deleev’s periodic table.
(3) This periodic law justifies the position of representative and transition elements, wh ch were palced in a same group

Answer

Answer

iii) Give the reaSOilS of the following:
Ionic Hydrides are called true Hydrides.
Reason: Alkali and Alkaline earth metal hydrides are called true hydrides ble they are non-volatile & they have high m.p and B.P. They are stable and hence called true hydrides.
• Lithium and Beryllium markedly differ from other members of their respec ive groups
Reason. Lithium belongs to group fA and Beryllium belongs to group IA of the periodic table their smaller atomic .size results in high charge densities of their ions due to which heat of hydration and electrode potential is high. Th s Lithium and beryllium markedly differ with other member of their respecnve group.

• Plaster of Paris is used in making plaster coats and moulds.
Reason: CaS04 Y2 H20 when mixed with water sets in about 5 minutes to a hard mass. This setting take place with expansion. This property permits to use in !:’e preparation of moulds used in surgery and castings.
• Why is the electronic configuration of Chromiam (Cr). 4s’, 3d5 instead of 4s2,3d4 while that of Copper (cu) is 45′,3d C instead of4s2,3d9?
Reason: The orbitals (sub-shells) tend to become half filled on completely filled, such configuration are stable than other orbitals. This tendency is called half tilled on completely fulled orbital rule. The configuration of Cr (24) is 1S2, 2S2,2p6r3S2, 3p6, 4S2 and 3~. According to rule it is 1S2,2S2, 2p6, 3S2, 2p6, 4S’ & 3d5.

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Question Answer

v) a) Write note on anyone: Detergents OR Tin Plating.
Detergents: Detergents are soap less cleansing agents. They are complex organic salts with long chain molecules.
Cleaning Action: Detergents are made up ,tof two parts.
i) Hydrophobic (water repelling)
ii) Hydrophilic (water attracting)
Hydrophobic part is the long hydro carbon chains which is covalently bonded, being non polar in nature, it attracts oil and grease with are also non-polar.
Hydrophilic part is small ionic group like sulphonate (S03-1 ) sulphate ~SQ,;-2),or hydroxyl group (OW). The presence of two groups allows the nixing of water with non polar substances such as oil and grease. A detergent removes dirt easily. Grease is an organic covalent compound. The hydrophobic part of the detergent readily dissolves in grease. The hydrophilic part of the detergent dissolves in water. 80 that slight agitation removes the grease and it is carried away with the water along with dirt.
Tin Plating:

“The art of making a coat of metallic tin on bases metals such as iron and copper for their protection from corrosion & poisoning is called tin plating.”

Process of Tin-Plating: There are two methods for tin-pating.
1. Mechanical process.
2. Electrolytic process

Mechanical Process: in nechanical process the iron sheets or mild steel are first thoroughly cleaned by dipping in warm dil H2S04 to remove the oxide film. The sheets are then washed with water and after drying, dipped the bath containinq molten tin. The sheets are then rolled to remove extra tin.
The Cu and brass utensils are first heated and then rubbed with some quantity of NH4CI, to remove the oxide film. A little of tin metal is rubbed over the hot surface and after sprinkling some NH4CI, the surface of the utensils are polished with a rag until a uniform layer of tin IS obtained.

Electrolytic Process: In this process, the iron sheets after cleaning, washing and drying are suspended into a bath containing a mixture of stannous chloride and HC!. Pure tin is made anode and the iron sheets are made cathode. On passing the current through the bath, tin starts depositing on the iron sheets. Thus iron sheets are tinned electrolytically.

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Castner-Kellner’s Process: NaOH is now manufactured by an electrolytic process, konwon as Castner Kellner’s Process.
Construction: NaOH is manufactured by the process of electrolysis of NaCI solution. The electrolyte is 25% w/w solution of NaCI. Anode is titanium plateswhere CI2 is liberated where as cathode is made up of stream of flowing mercury.
Working: NaCI is ionized as process starts:

Answer

Answer

The mercury is recycled to dissolve more of Na. Denuder is packed with graphite blocks as hydrogen is easi!y liberated over graphite surface.

The solution which flows out from denuder, is a solution of NaOH, which is evaporated to dryness.

Manufacture of Chlorine by Nelson Cell:

See on Page # 335.

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Question Answer

b) What are outer and inner transition elements and how many series of each of them are present in the periodic table? Also write the names of the inner transition series

Outer Transition Elements: The elements in which the last electron enters (n-1) d orbitals are called d-block elements. They are also called as outer transition elements. The valance shell configuration of these elements ranges from ns2 (n-1 ) d1 to ns2 (n-1) d’O.
Inner Transition Elements: The elements in which the last electron
enters (n-2) f orbital are callec f-block elements or outer transition elements. The valence shell configuration of these elements are:
ns2 (n-1) d’, (n-2) f 1-14
They are further divided into two series.
Lanthanides
Actinides

Outer Transition Elements have following series:
i) from Scandium, SC (Z=21) to zinc, Zn (Z=30)
ii) from yttrium, Y (Z=39) to cadmium, Cd (Z=48)
iii) from Lanthanum, La (Z=57) to mercury, Hg (Z=80)
Inner Transition Elements Constitute Two Series Which are:
i) from Cerium, (Z=58) to Lutetium (Z=71) called Lanthanides.
ii) from Actinium (Z=89) to Lawrencium (Z=103) called Actinides.

ORGANIC CHEMISTRY

ix) Define:
Zwitter Iron:
A dipolar, charged but over all electrically neutral Ion is cauec zwitterions.

formula

formula

Catenation
The ability of carbon atoms to bond itself to other carbon atoms froming long chains, branched chains, rings & compounds with chain & rings is called catenation.
Polymerization
” Chemical combination of two or more molecules to form single large molecule is called polymerization and the molecule is called polymer.”
Types of Polymerization: There are two types of polymerization.
i) Additional polymerization.
ii) Condensation polymerization.
Addition Polymerization: When unsaturated monomers undergo self combination, long chain, branched or unbranched structures are
formed. This type of polymerization is called Addition polyrnerizatlon.

example

example

Condensation Polymerization: This type of polymerization occurs between two different. types of monomers having different functional groups. In condensation polymenzation elimination of water takes place.

Bakelite

Bakelite

Metamerism
It is a type of isomerism which is”” exhibited by the compounds having same functional group but different alkyl groups attached to the same multivalent atoms

formula

formula

formula

formula

xii) Define and classify Vitamins. Explain vitamin B – Complex and vitamin C.
Vitamins are organic substances and quite different from carbohydrates, proteins and lipids. These are normally available to the body from the diet we take, for the purpose to regulate energy transformation and metabolism.
Classification of Vitamins: Vitamins are classified on the basis of their solubility.
1. The vitamins which are soluble in fats or in fat solvent are called fat soluble vitamins. Vitamin A, D ,E ,and K are examples of fat soluble vitamins.
2. The vitamins which are soluble in wpter are known as water soluble vitamins and are observed in juices of fruits. Examples are vitamin B- complex and vitamin C.
Vitamin B – Complex: A group of water soluble vitamins obtained from the liver, yeast and other sources are found effective for growth and appetite, reduce sugar content in diabetes, help in treatment of the various infections and are collectively known as Vitamin B complex.
Vitamin C: It is also called ascorbic acid. It is abundantly found in fresh fruits such as orange, lemon, grape fruit, strawberries and guava. In vegetables it is present in tomatoes, cauliflower, cabbage, and potatoes.it is absent in meat, egg and fish.it is soluble in water. It is easily destroyed by heat and oxidation, washing of vegetables and improper cooking specially in material like copper and iron. Deficiency of vitamin C lowers the body resistance to infection and causes bleeding of teeth. Its deficiency in .severe cases causes anemia and scurvy.

Question and daigram

Question and daigram

Hybridization = sp,
Structure of Ethyne: Each carbon atom in acetylene is attached to one hydrogen atom by a single covalent bond (ll – bond) and to-another carbon atom by a triple bond. Thus eaeh carbon uses sp 1 hybridized orbitals and two unhybridized 2p orbitals (P, and Pz) to form its pi – bonds (n – bond).

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Answer

Answer

SECTION ‘C’ (DETAILED QUESTIONS ANSWER)

3.a) What are binary compounds of Hydrogen? Classify them, Explain covalent and polymeric hydrides.

Binary Compounds of Hydrogen: The compounds of hydrogen with other elements are called binary compounds or Hydrides.
Classification:
1. Ionic hydrides
2. Covalent hydrides
3. Complex hydrides
4. Metallic hydrides.
5. Polymeric hydrides.
6. Borderline hydride.

Covalent Hydride: Compounds of hydrogen with elements of group IliA to VilA are called covalent hydrides. They can be prepared as follow:

formula

formula

Hydridesof group iliA & IVA are neutral.
Hydrides of group VA are basic while
Hydrides of VIA & VilA are acidic.

Polymeric Hydride: First two members of group IIA i.e, Be & Mg form hydrides having formula (BeH2)n and (MgH2)n because large number of BeH2 and MgH2 molecules are polymerized therefore they are known as polymeric hydrides.

formula

formula

3.b) Describe the manufacture of Sulphuric acid by Contact process. Draw the flow diagram.
See on Page # 350

c) Define Alum and write chemical formulae of three alums.
The series of double sulphates of mono valent & trivalent metals containing 24 molecules of water of crystallization are known as Alums.
Examples: There are various compositions of Alum. The alums are usually the sulphates of sodium, potassium or ammonium with aluminum, iron or chromium.

formula

formula

4.a) How is pure Copper obtained from roasted pyrite ore?
See on Page # 349.

4.b) Complete the following equations:

formula

formula

4.c) Write the chemical formulas of the following:

formula

formula

ORGANIC CHEMISTRY

5.a) What is Fermentation? How is Ethyl alcohol obtained by
fermentation of:
* Starch
* Molasses
See on Page # 354.

5.b) What happens when:
Methanal is treated with Phenyl hydrazine

formula

formula

Phenol is treated with Bromine water

formula

formula

Phenol is treated with red hot Zinc dust

formula

formula

Ethyne is reacted with Iodine in presence of Ethanol

formula

formula

5.c) What is orientation in Benzene? Explain orientation in monosubstituted benzene. Name three each of ortho- para and meta directing groups.
When a monosubstituted benzene undergo electrophilic attack, the substituent already present on the ring directs the incoming group to
ortho- para or meta positions, depending upon the nature of group already present.
i) Ortho-para directing and Activating group: The following groups activate the benzene ring and decide the o.p-posttion for next incoming substituent. ~9T.h.ese groups usually are elec.t.ron.; donating groups). E.g.,

formula

formula

These groups direct the ortho-para position in the ring. Example: Formation of ortho and para nitro benzoic acid from toluene.
in Meta directing and deactivating groups: The following groups deactivate the benzene ring and direct the incoming group to meta position. (Usually these groups are electron withdrawing groups). Nitro (N02), Suiphonic acid (S03H), Carboxylic acid (COOH), esters (COOR). aldehydes (CHO), Ketones (-COR), trifluoro methyl (-CF3). The groups pull the electron density towards themselves and deactivate the ring.

6.a) Explain electrophilic substitution in Benzene with reference to:
(i) Friedel- Craft’s acylation and (ii) Sui phonation reactions.
EJectrophilic substitution reaction of Benzene: In benzene molecule, there are six (n) pi-electrons, so it should behave like unsaturated compound like alkene but it does not undergo addition reactions easily. It behaves ~ saturated compound in presence of Lewis  Acid due to fact the in benzene pi (n) electrons which are delocalized. When an electrophile [E+] attacks on this pi electron system then substitution takes place after the removal of hydrogen atom from the benzene ring by the nucleophile [Nul and E+ attached with benzene ring

formula

formula

formula

formula

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Question Answer

Posted on December 31, 2015 in 2nd Year 2012 Karachi Board Past Papers

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