Chemistry Solved Past Paper 2nd year 2011 Karachi Board

SECTION ‘A’ (MULTIPLE QUESTIONS ANSWER)

1. Choose the correct answer from the given options:

i) The sweetest sugar is:
• Fructose
• Glucose
Sucrose
• Lactase

ii) Ethylene is used aslin:
anaesthetic
• preparing Mustard gas
• ripening Of fruits
• all of these

iii) All noble gases fulfill the octet rule except:
• Ne
• Ar
He 
• Xe

iv) The elements of same group have the:
• same number of electrons
• same number of protons
same number of valen e electrons
• same valence shells

v) Hydrogen shows the oxidation state (s):
• Zero only
• -1 only
• +1 only
All of these

vi) Elements belonging to the same group in Hie periodic table are:
• Ca and Na
Ca and Be
• Ca and Li .
• Ca and K

vii) Molecular formula for Tineal is:
• H3B03
Na2B40710H20
• H2B407
• Na2B07.7H20

viii) The substance which contains two or more metals is called: ‘
• Polymer
• Homologous .
Alloy
• Allotrope

ix) The compounds 1 – butene and 2 – butene are:
Position isomers
• Chain isomers
• Fu ctional group isomers
• Metamers

x) Molecul formula of Chloroform is:
• CH3CI
CHI3
• CH2CI2
• C6hr

xi) General formula kyl h::.lides is:
CnH2nX .
• Co H2n-2 .
• C H2r+ X
•. CnHoX

xii) Blood cancer is caused by:
Methane
• Butane
• B
• Ethane

xiii) A carbon atom ha n9 a positive ch r Is called:
• Hydroxide ion
• Hal d Ion
• Carbonium ion
• Carban 01

xiv) Methylated spirit is I iixture of:
• CH30H and CH~CI
• CHjOrl ana CH4
• CH30H and C2H
• CH30H and HCI

xv) Carbon atom of carbon r…u•p is hybridized as:
• sp
• sp2
sp3
• sp4

xvi) Tollen’s reagent is:
• Ammoniacal cupro id·
• Ammoniacal C’ pr()W~ C.”vi ~t;
• Ammoniacal silver’ ()
Ammoillacal silver nil’ Clle

xvii) Fruity smell is produced hen C2H50H is rea~ted with:
• CH3COCH3
• pel
• PCls
H3COOH

SECTION ‘B’ (SHORT QUESTIONS ANSWER)

INORGANIC CHEMISTRY

Question Answer

Question Answer

Electron Population
The ratio between number of electrons present in the outP;’most shell and the maximum capacity of electrons in that she’.I, is called  electron population.

Perlodicity-of elements

The recurrence of elements after interval is called periodicity of elements

Define and classify bin _.y compounds of Hydrogen. Explain Ionic hydrides, givi, ,y two preparations and two reactions.
Hydrogen combines with other elements and forms binary compounds whiGh are called hydrides. Hydrogen forms compounds with all types of metals nonmetals and elements except inert gases.
BINARY COMPUNDS OF HYDROGEN:
1. Ionic hydrides
2. Covalent hydrides
3. Complex hydrides
4. Metallic hydrides
5. Polymeric hydrides
6. Borderline hydrides

IONIC HYDRIDES: These types of hydrides are formed by the metals of group IA and group IIA except Be and mg. in these hydrides metal atoms forms poisitive ions by losing valence electrons and hydrogen forms negative ion oy gaining that electron. They possess salt like characters therefore also called saline hydrides.

PREPERATION REACTIONS

PREPERATION REACTIONS

iii) How is caustic soda prepared by Castner Kellner’s Cell? Give advantages and disadvantages of the process.
Ans: See on Page # 375.

Advantages of Process:
1. The process is very efficient.
2. Product formed is of high purity.
3. The possible reaction b/w NaOH & CI2 is avoided by obtaining NaOH & CI2in separate chambers.
Disadvantages of Process:
1. Process consumes large quantity of electricity.
2. Some vapours of Hg escape from factory which contaminates water & cause water pollution.

iv) (a) Discuss any two of the following properties ‘of transition metals:
* Magnetic Properties
Many compounds of the transition elements are paramagnetic i.e.. they are attracted by magnetic field. Para magnetism is generally caused by presence of unpaired electrons spin in the ions and atoms of the elements.

Formation of Coloured Compounds
The transition metal complex ions are colored (except Zn). Crystal field theory fully explains the color of the complex, ion. According to C.F.T. the bonding b/w ligands & metal ion is electro static. The ligands surrounding the metal ion create an electro static field around its dorbitals. This splits five degenerated d-orbitals into two sets with different energies i.e. a higher energy pair e.g, and a lower energy pair 12g.
In many cases, the energy difference b/w  blw two sets of d-orbitals in equivalent to a wave length in the visible region. Thus by absorbing visible light, an electron may be able to move from lower energy Set (tzg) to higher energy set (eg). In doing So, some of the components of wave length of white light is removed, so the remaining component wave length of the light reflected or transmitted shows the color to the viewers.

Formation of Complexes
Transition element form co-ordinate compounds which are also called complexes. This is because they have small highly charged ions and vacant d-orbitals of suitable energy. The vacant d-orbitals accept  lone pair electrons from atoms, ions or molecules called liqands.
(b) What is Lunar caustic? Give the equation for its preparation.
Lunar Caustic: Silver nitrate (AgN03) is also called Lunar Caustic.
Preparation: Silver nitrate is prepared by dissolving Ag-metal in dil HN03. On crystallization, the long crystals or sticks are formed

3Ag + 4HN03 —-+ 3AgN03 + NO +H20

v) Give reasons:
Alkaline earth metal ions are more strongly hydrated than alkali metal ions.
Alkaline earth metals are more strongly hydrated than alkali metals ions because M+2ions have a strong electric field, more nuclear charge and small size as a result II A metal iorfs are hydrated strongly than IA ions.

Atomic hydrogen is more reactive than molecular hydrogen.
Atomic Hydrogen has one electron in its outermost orbit. Thus it can accept or donate one electron to reach the electronic configuration of the nearest inert gas. On the other hand, molecular hydrogen consists of two atoms of hydrogen linked together by a covalent bond. Thus, there is no extra electron for reactivity. For the above reason, atomic hydrogen can readily react with little amount of energy. Molecular hydrogen requires greater amount of energy so as to form atoms of hydrogen first which will react.

* Most of the transition elements and their compounds are paramagnetic.
The transition metals and their compounds show magnetic properties. Many compounds of the transition metals are paramagnetic because of unpaired electron spins in the atom.

* H20 and NH3 act as ligands but H30+ and NH ~ do not.
In H20 and NH3, there is a lone pair of electron which is available for donation. Therefore they act as ligands while in a case of H20+ and NH ~ Ion pair of electron is not available-in fact it is consumed in making of coordinate covalent bond.

vi) Give equations for the following:
Reaction of Na2C03 with Silica
Na2C03 + Si02 —7 Na2Si03 + CO2
* Reaction between Sodium and Oxygen
2Na + O2 —-t Na202
* Action of heat on Blue vitriol
CuS04.5H20 —-t CUS04 + 5H20
* Reaction between K2Cr207 and KOH
K2Cr207 + 2KOH —7 2K2Cr04 + H20

vii) (a) Give the equations for the preparation of the following:
* Bleaching Powder.
Ca(OHh + CI2 —-t CaOCI2 + H20
* Boric acid
BN + 3HzO —-t H3B03 ~ NH3

(b) Give points of resemblance of Hydrogen with fA and VII·A groups of periodic table.
Resemblance of Hydrogen With Group IA:
1) Like alkali metals hydrogen has one electron in its valence shell.
2) Valance shell electronic configuration of hydrogen and alkali metal is same.
3) Like alkali metals hydrogen can also form halides. Both hydrogen
an alkali metals are good reducing agents.
4) Like alkali metals hydrogen can also form compounds with nonmetals.
Resemblance of Hydrogen With Gro VilA:
1) Both Hydrogen and Halogens require one electron to complete their valence shell.
2) Both hydrogen and Halogens are non-metals(Except iodine which has partial metallic character).
3) Both hydrogen and Halogens acts as negative Ions W with metals.
4) Their molecules are diatomic.
5) Like Halogens, hydrogen can bond.

Question Answer

Question Answer

Question Answer

ix) (a) Draw and explain the orbital structure of Ethene.
ORBITAL STRUCTURE OF ETHENE:
Molecular fbrmula = C2H4
Empirical. formula = CH2
Molecular mass = 28
Empirical formula mass = 14
Homologou series = alkene
COMPOSITION OF ETHENE’
Ethene molecule consists of two carbon atoms and four Hsatoms i.e. CH2 = CH2
NATURE OF HYBRIDIZATION:
In ethene molecule each C-atom is Sp2-hybridized. Due to Sp2- hybridization each C-atom generates three Sp2-hybrid orbitals. In this way there exist six S~-hybrid orbita.. These Sp2-orbitals are arranged in trigonal order and 1200 apart. Remaining ‘2pz’ unhybrid orbitals of carbon atom are placed perpendicular to the plane of Sp2- orbitals.

daigram

daigram

SIGMA BOND FORMATION:
One Sp2-hybrid orbital of C-atom overlaps with One Sp2-hybrid orbital of second C-atom to produce one sigma bond between two carbon atoms. Remaining two Sp2-orbitals overlap ith two H-atom to produce sigma bond. ‘2pz’ orbitals of two C-atoms are un-hybridized and make parallel overlapping to produce pi-bond as shown below

(b) Distinguish by simple chemical tests:
• AldehYde and Ketone

AldehYde and Ketone

AldehYde and Ketone

Alkene and Alkyne

Alkene and Alkyne

Question Answer

Question Answer

Question Answer

Question Answer

Question Answer

Question Answer

Silver Acetylide

Silver Acetylide

xiv) Define and classify Vitamins. Explain vitamin B – complex and vitamin C.
Vitamins: 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 water 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.

xv) (a) What are Phenols? Classify them,
Phenols are organic compounds containing hydroxyl group directly attached to the ring carbon atom.
Classification:
1. Monohydric
2. Dihydric
3. Pyrogallo

(b) State Markownikoffs rule. Write the equation for the reaction between Vinyl bromide and Hydrogen bromide.
Markownikoff’s rule: AccorDing to this rule the negative part of any hydrogen halide attacks to carbon of any compound which contains least number of hydrogen atom.

formula

formula

xvi) Write notes on any two of the following
Glass
Glass is one of the most important artificial silicates. Ordinary glass or soda glass is a mixture of sodium silicate and calcium silicate
Preparations: It is produced by heating sand, soda or sodium sulphate and lime stone in furnace at 1400°C.
Na2C03 + Si02 –+ Na2Si03 + C02.
CaC03 + Si02 –+ CaSi03 + C02.
Na2Si02 + CaSi03 +’ 6Si02 ~ 2C02 -t, Na20.6Si02

Glass is not true solid, because molecules are not arranged in definite pattern. It is. a super cooled liquid i.e. a solid solution without crystallization. The molecules are arranged in random positions.
Types of Glass:
i) Ordinary Glass:’ It is a mixture of sodium & calcium silicates. It is manufactured from sand, soda and lime stone. They are used for making chemical glass ware.
ii) Pyrex Glass: It is a borosilicate mixture, which is produced by using boron oxide in place of some of silica. This glass can withstand sudden changes in temperature.
iii) Colored Glass: It is manufactured by adding certain transition metal oxides. For ego
CuO give light blue color
CoO give dark blue, color
Cr203 gives green color.
Detergent.
Detergents are soap less cleansing agents. They are complex organic salts with long chain molecules.
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 (S04-2), or hydroxyl group (OW). The presence of two groups allows the mixing of water with non polar substances such as oil and grease. A detergent removes dirt easily. Grease is an organic covalent compound.

Answer

Answer

SECTION ‘C’ (DETAILED QUESTIONS ANSWER)

3.a) Giye the advantages and defects of Mendeleev’s periodic table. Explain how modem periodic table is divided into blocks. Also write general electronic configuration of each
block.
Advantages: 1. Study of Elements: By the comparison of the properties of elements in different groups and; periods, the study of 110 elements is simplified.
Prediction of New Elements: Mendeleev left vacant places for the undiscovered elements, Mendeleev discovered the three new elements and their properties with the help of his periodic law. At present all the elements are discovered and there is no vacant place in the periodic table:
Correction of Doubtful Atomic Weights: The doubtful atomic weights of certain elements were corrected. For example the atomic weight of beryllium was corrected from 13.5 to 9. With this atomic weight beryllium was given a position between Li and Boron.

Defects of Mendeleev’s Periodic Table:
1. Position of Isotopes: no place is given in the table for different isotopes of an element.
For example , for oxygen only 1O is given a place while other isotopes 170 and 1 0 are not given a place
2. Position of Rara hs: In the 6th period, 15 elements called lanthanides or rare earths are in same position (III group).
3. Anomalous Pairs of E ements: Ce-rtaiA elements of higher tomic weights precede those of lower omic weights.
Division of Modern Periodic Table: periodic table is divided into 4 types i.es,p,d,f blocks based on electronic configuration.
1. The Noble Gases: They are colorless, un tive and diamagnetic. Treir electronic configuration is ns2, np” except heli
2. Representative Elements: These elements include I and nonmetals.
Some are diamagnetic and some are paramagn . mclude elements of sand p blocks.
(i) S _ Block Elements: The elements in which last electron enters ns orbitals are called s block elements. The elements of group I and II are s block elements. Their elect;onic configuration varies from ns1 to ns2.
(ii) P – Block Elements: The elements in which p~orbital begin to fill p to np6 are called p block elements. Elements of groups III – A to VII A and zero groups are included into it.
(iii) d _ Block Elements: The elements in their atomic state or ir their common oxidation state in which last electrorn enters to (n-1) d orbital are called dblock elements. d block elements c nsist of 3 series.
(iv) f _ Block Elements: The elements in which inner f orbital are filled by progressive addition of electrons are called f bock etements they have two series

Answer

Answer

4.a) Give with diagram the extraction of pure Aluminium from pure Aluminium oxide. What are Ammonal and Aluminium bronze?
Mention their uses.
Extraction of Pure Aluminium:
Working of the Cell: On electrolysis, aluminum is collected at cathode at the bottom of tank. Oxygen is collected at carbon anode which reacts with this oxygen to form C02. Thus carbon anode is consumed and has to be replaced with new one after sometime.
Chemical Reaction:

Chemical Reaction Reaction At anode Reaction At Cathode Overall Reaction

Chemical Reaction Reaction At anode Reaction At Cathode Overall Reaction

About 99.5% pure aluminum is obtained. The impurities present are iron and silicon

Refining of Aluminum by Hoop’s Electrolysis: The impurities such as Cu, Si and Fe are removed by Hoop’s method of electrolysis. The cell is an iron tank which has three different layers one over the other of different specific gravity.
(i) Top Layer: it contains pure AI which acts as a cathode.
(ii) Middle Layer: it contains cryolite (Na3 AIF6) and BaF2.
(iii) Bottom Layer: it contains impure AI with impurities such as CU,Si, Fe.
When current is passed A13+ions from midd e layer go to top layer and arte discharged there as pure AI. At the same time , equivalent amount of AI from impure al is passed into the middle layer. whereas impurities are settled down at the bottom. 99.9 % AI is obtained by this method.
Chemical Reaction:
Na AIF6 —.) 3NaF + AIF3
AIF3 –t AI+3+ 3F
Reaction at Catode:
AI·3 + 3e –t AI
When the currant is passed through it the impurities are removed and 99.99% pure aluminum is obtained.

Ammonal & Aluminum Bronze:
Ammonal: A mixture of AI powder, Aluminum nitrate is known as amrnonal which is used in explosive bombs. Aluminum Bronze: It contains 10% of AI and 90% of Cu. It has a beautiful golden colour. It is tough and more resistant to corrosion than AI. it is used in the manufacture of imitation jewel,ery coins and statues etc.

Eleclrolysis of Pure Alumina

Eleclrolysis of Pure Alumina

b) Write notes on any two of the following:
• Lead pigments
Ans: See on Page # 332.

• Corrosion and its prevention
Ans: See on Page # 333.

• Allotropic forms of Carbon
Ans: There are 2 allotropic forms of carbon: I
a: crystalline b. amorphous
1. Crystalline Form: There are 2 crystalline forms:

Diamond: Is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic.
Diamond is an, optically isotropiccrystal that is transparent to opaque. Diamond is the hardest naturally occurring material known.The chemical bonds that hold the carbon atoms in diamonds together are weaker than those in graphite. In diamonds, the bonds form an inflexible three-dimensional lattice, whereas in graphite, the atoms are tightly bonded into sheets, which can slide easily over one another, making the overall structure weaker.

Graphite: Unlike the tetrahedral arrangement of atoms in diamond, the carbon atoms in graphite are arranged in the form of hexaqonal rings in layers. Each carbon is bonded to only three other carbon atoms in that layer. Different layers of graphite are held together by rather weak forces. Hence they can slide over one another. This is one reason why graphite scales off easily and can mark impressions on substrates. Because of this property, it is also used as a lubricant.
Amorphous Form: There are many amorphous forms of carbon like coal, coke, charcoal, lampblack etc

ORGANIC CHEMISTRY

Question Answer

Question Answer

Question Answer

Question Answer

Question Answer

Question Answer

6.a) Expiain the structure of Benzen’e by molecular orbital treatment along with orbital structures. Benzene acts as a saturated and unsaturated compound. Justify this statement
by r quations.
Ans: See on Page # 336.

Stability of Benzene Ring:
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 IT electron above & below the surface of ring are responsible for substitution reaction of benzene. .
In these type of reactions an electrophilic attacks the n; – system of benzene to yield delocalized carbocation known as arenium ion. This breaks the cyclic system of 1′: electrons, blc when arenium ion is formed, one carbon become Sp3 hyberdized. This causes instability and to overcome this instability the arenium ion loses a proton from the carbon that bears the electrophile. The loss of proton results in regeneration of 1[ – system which restores the stability of the ring.

Benzene as a Saturated and Unsaturated hydrocarbon: Like other saturated hydrocarbons benzene does not give reaction with KMn04, and addition reaction.

no reaction

no reaction

formula

formula

 

Posted on December 31, 2015 in 2nd Year 2011 Karachi Board Past Papers

Share the Story

Back to Top
Share This