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Chemistry I Paper I

Section A I Answer all the questions each carries two marks 10 2 = 20 M 1. Which of the gases diffuses faster among N2, O2 and CH4? 2. What do you meant by significant figures? 3. What is meant by ionic product of water? 4. Explain the term SYNGAS 5. What do you mean by autoprotolysis? Give the equation to represent the autoprotolysis of water 6. What is boric acid polymeric? 7. Give two uses of aluminum 8. What is ozone hole? Where was it first observed? 9. Name the major particulate pollutants present in the polluted air 10. How is nitrobenzene prepared?

Section B II Answer any six questions. Each carries four marks 6 4 = 24 M 11. State and explain Daltons law of partial pressures 12. Balance the following redox reaction in basio medium by ion electron method P4 + OH PH3 + HPO 13. What is entropy? Explain with examples 14. State law of chemical equilibrium? What is Kc for the following equilibrium when the equilibrium concentration of each substance [So] = 0.6. M, [O] = 0.82 M, [So] = 1.90 M 2SO2(g )+O2(g) 2SO3(g ) 15. What do you know about castner Kellner process? Write the principle involved in it 16. Write a short note on fullerene 17. Explain the formation of co ordinate covalent bond with one example. 18. Explain the hybridization involved in PcZ5 molecule

Section C III Answer any two of the following. Each question carries 8 marks 8 2 = 16 M 19. How are quantum numbers n, z and mc arrived at? Explain the significance of these quantum numbers 20. Discuss the construction of long form of periodic table 21. Describe any two methods of preparation of Benzene. Explain ay four electrophilic substitution reactions of benzene.

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Acid Base Conjugate acid

Conjugate base

Section A 1. Which of the gases diffuses faster among N2, O2 and CH4? Ans. CH4 gas diffuse faster among N2, O2 and CH4. Reason: CH4(16) has low molecular weight than N2(28) and O2(32). 2. What do you meant by significant figures? Ans. The meaningful digits which are known with certainly are called significant figures. The uncertainty in the experimental (or) calculated values is indicated by mentioning the number of significant figures. 3. What is meant by ionic product of water? Ans. At a given temp. the product of the concentrations of H+ and OH- ions in water is called ionic product.

Ionic product Kw= [H+] OH- At 25 CKw = 1.008 10-14 mole2/lit2 4. Explain the term SYNGAS Ans. The mixture of CO and H2 which is used for the synthesis of methanol and a number of hydrocarbons is called SYNGAS. It is also called as synthesis gas. Preparation: C(s) + H2O(g) CO(g) + H2(g) This reaction is called Coal gasification 5. What do you mean by autoprotolysis? Give the equation to represent the autoprotolysis of water Ans. Equation to represent the autoprotolysis of water. Water has the ability to behave as an acid as well as base. It behaves as an amphoteric substance. The self Ionizing property of water is called auto protolysis. The equation that represents the autoprotolysis of water is as follows. H2O(l) +H2O(l) H3O

+ (aq) + OH-(aq)

6. What is boric acid polymeric? Ans. Boric acid has layer like lattice. In the structure planar BO3 units are joined by hydrogen bonds and forms a polymeric structure 7. Give two uses of aluminum Ans. Uses of aluminum: Aluminum used in packing Aluminum is used in utensil making Aluminum alloys are used in shaping of pipes, tubes, wires etc Aluminum alloys are used in making air craft bodies.





H2SO4 < 60

Number of moles of the first gas

Total number of moles in the mixture of gases

+ H2 O

NO2

8. What is ozone hole? Where was it first observed? Ans. The depletion of ozone layer is commonly known as ozone hole. It was first observed in Antarctica over the South Pole. It was reported buy atmospheric Scientists working in Antarctica. 9. Name the major particulate pollutants present in the polluted air. Ans. The major particulate pollutants present in troposphere are dust, mist, fumes, smoke, smog etc. 10. How is nitrobenzene prepared? Ans. Benzene undergoes nitration with nitration mixture (conc. HNO3 + conc. H2SO4) at less than 60 to form nitrobenzene.

+ HNO3

Section B 11. State and explain Daltons law of partial pressures Ans. Daltons law of partial pressures: The total pressure exerted by a mixture of chemically non-reacting gases at given temperature and volume is equal to the sum of the partial pressure of the component gases. Explanation: Consider a mixture of three gases in a vessel. Let P1, P2, P3 be the partial pressures of the three gases in the mixture. According to Daltons law of partial pressures, the pressure (p) of the gaseous mixture is at the same temperature. P = P1 + P2 + P3 Let n1, n2, n3 be the number of moles of three gases respectively in the mixture. Let V be the volume of the mixture of gases at T K Temperature. According to ideal gas equation

P1 = n1RTV P2 = n2RTV P3 = n3RTV

P = RTV (n1 + n2 + n3)

Since n1 + n2 + n3 = n

P = nRTV

Or P = n1RT/VnRT/V = n = x1

Where x1 is the mole fraction of the first gas and given by x1 = P1 = X1P In a similar way P2 = X2P and P3 = X3P





(Low entropy) (moderate) (high entropy)

Partial pressure = mole fraction total pressure. 12. Balance the following redox reaction in basio medium by ion electron method P4 + OH PH3 + HPO P4 + NaOH + H2O PH3 + NaH2PO2 P4 + OH - PH3 + H2PO2 P4 + OH

- PH3 + HPO Reduction half cell P4 PH3 P4 4PH3 P4 + 12H2O 4PH3 + 12OH (M balanced) P4 + 12H2O + 12e

- 4PH3 + 12OH 3P4 + 24OH

- 12H2PO + 12e- 4P4 + 12H2O + 12e

- 12H2PO + 4PH3 Here P4 is oxidizing agent as well reducing agent. Oxidation half cell P4 H2PO P4 4 H2PO (P balanced) P4 + 8H2O 4 H2PO (oxygen balanced) P4 + 8H2O + 8OH

- 4 H2PO + 8H2O (Hydrogen balanced) P4 + 8OH 4 H2PO + 4e- 13. What is entropy? Explain with examples Ans. Entropy(S): Entropy is taken as a measure of disorder of molecules (or) randomness of the system. Greater the disorder of molecules in a system, the higher is the entropy. Entropy is a state function. It depends on the temperature, pressure of the state.

Entropy change, S = qrev

[qrev = heat absorbed by system isothermally and reversibly at T ]

For a spontaneous process in a isolated system the entropy change is positive. ( S = positive) S total = S system + Ssurroundings Ex: Solid heat liquid heat Vapour 14. State law of chemical equilibrium? What is Kc for the following equilibrium when the equilibrium concentration of each substance [SO] = 0.6. M, [O] = 0.82 M, [SO] = 1.90 M 2SO2(g )+O2(g) 2SO3(g ) The ratio of product of molar concentrations of the products to the product of molar concentrations of the reactants has a constant value. This is known as the equilibrium law (or) law of chemical equilibrium. Given equation is

2SO2(g )+O2(g) 2SO3(g )





Hg

Given [SO] = 0.6. M, [O] = 0.82 M, [SO] = 1.90 M

Kc = [SO3]2[SO2]2[O2] = [.][.][.]

= .

. . = .. = 12.22 15. What do you know about castner Kellner process? Write the principle involved in it Ans. Castner Kellner process is a commercial method used for the preparation of Sodium hydroxide.

In this process Sodium hydroxide is prepared by the electrolysis of Sodium chloride in Castner Kellner cell.

Brine Solution is electrolyzed using a mercury cathode and a carbon anode. Sodium metal is formed at cathode and it combine with mercury to form sodium amalgam. Chlorine gas is evolved at anode. The amalgam is treated with water to form sodium hydroxide.

Cell Reactions: 2Nacl 2Na+ + 2Cl-

2Na+ + 2e- 2Na amalgam 2Cl- Cl2 + 2e

- 2Na amalgam + 2H2O 2NaOH + 2Hg + H2 This process is also called as mercury cathode process.

16. Write a short note on fullerene Ans. Fullerenes: Fullereness is one type of crystalline allotropes of carbon.

These are formed by heating graphite in an electric arc in presence of inert gases such as Helium (or) Argon. These have smooth structure without dangling bonds. Hence fullereness are only the pure forms of carbon. C60 molecule is called Buck minster fullerene and its shave was like a soccer ball.

C60 contains twenty 6 membered rings and twelve 5 membered rings. In C60 6 membered rings can combine with 5 (or) 6 membered rings while 5 membered rings only combine with 6 membered rings.

In Fullerens each carbon undergoes Sp2 hybridization. Fullere has aromatic nature due to delocalization of electrons in unhybrid p - orbital. The C C bond length in these compound lies between single and double bond lengths. Spherical fullerene are also named as Bucky balls. The ball shaped molecule has 60 vertices. The C C bond distances are 1.43 A and 1.38 A respectively.





N : H + or NH4

+

H

17. Explain the formation of co ordinate covalent bond with one example. Ans. Co ordinate covalent bond (dative bond) is a special type of covalent bond. It is proposed by Sedgwick. It is formed by the sharing of electrons between two atoms in which both the electrons of the shared electron pair are contributed by one atom and the other atom nearly participates in sharing. The bond is represented as ( ) an arrow starting from the donor atom and directed towards the acceptor atom. Examples: 1) Ammonia Boron tri fluoride H3N: BF3 Ammonia combines with Boron tri fluoride to give ammonium boron tri fluoride In ammonia nitrogen has a complete octet and also it has a lone pair of electrons. In BF3 the boron atom has a total of six electrons after sharing with fluorine. Nitrogen donates the electron pair to boron to form a co ordinate covalent bond between ammonia and boron tri fluoride.

2) Ammonium ion (NH4+) 3) Hydronium ion (H3O

+)

H

H

H N : + BF3

H

N : H

H

BF3

Donor Acceptor Ammonia boron tri fluoride

H

H

N

+

N

H

H

N -

H

H

H+ + H3O

+

. .

. .





3S2 3P3 3d

0

3S1 3P

3 3d

1

Properties of co ordinate covalent bond 1) The bond do not ionize in water 2) The compounds are generally soluble in organic solvents and are sparingly soluble in water. 3) These compounds exhibit space isomerism because the bond is rigid and directional. 4) The bond is semi polar in nature. So their volatility lies in between covalent and ionic bonds. 18. Explain the hybridization involved in Pcl5 molecule. Ans. In Pcl5 the electron configuration of phosphorus is P (Ground State) : 1S2 2S2 2P6 P (Ground State) : 1S2 2S2 2P6 2) Phosphorus undergoes SP3d hybridization by inter mixing of one S orbital [3S] , three P orbits 3Px,3Py,3Pz and one d orbital. These five hybrid orbitals overlap. The Pz orbitals of chlorine atoms forming five Osp3d-s bonds. Out of these five p cl bonds three are coplanar and the remaining two are in the axial position. There by pcl5 acquires the trigonal bipyramidal shape. The molecule contains two bond angles 90 and 120





Section C

19. How are quantum numbers n, z and mc arrived at? Explain the significance of these quantum numbers Ans. In general a large no. of orbitals are possible in an atom. These orbitals are distinguished by their size, shape and orientation. An orbital of smaller size means there is more chance to find electron near the nucleus. Atomic orbitals are precisely distinguished by quantum numbers. Each orbital is designated by three major quantum numbers. 1) Principal quantum number (n) 2) Azimuthal quantum number (z) 3) Magnetic quantum number (m) 1) Principal quantum number: The principal quantum number was introduced by Nelis Bophr. It reveals the size of the atom (main energy levels). With increase in the value of n the distance between the nucleus and the orbit also increases. It is denoted by the letter n. It can have any simple integer. Value 1, 2, 3, . but not zero . These are also termed as K, L, M, N etc. The radius and energy of an orbit can be determined basing on n value.

The radius of nth orbit is rn = n2h242me2

The energy of nth orbit is En =

2) Azimuthal quantum number: It was proposed by Sommerfeld. It is also known as angular momentum quantum number or subsidiary quantum number. It indicates the shapes of orbitals. It is denoted by . The values of depend on the values of n, has values ranging from o to (n-1) i.e. = 0, 1, 2(n-1) The maximum number of electrons present in the sub shells S, p, d, f are 2, 6, 10, 14 respectively.

Sub shell

- value

Shape

S

=0

Spherically symmetric

P

=1

Dumb bell

D

=2

Double dumb bell

f

=3

Four fold dumb - bell





m = +3 m = +2 m = +1

m = -1 m = -2 m = -3

0 = 3

Energy levels and sub shells

3) Magnetic quantum number: It was proposed by Lande. It shows the orientation of the orbitals in space. p orbital has three orientations. The orbital oriented along the x axis is called px orbital, along the y axis is called py orbital and along the z axis is called pz orbital. In a similar way d orbital has five orientations. They are dxy, dyz, dx2-y2 and dz2. It is denoted by m. Its values depends on azimuthal quantum number, m can have all the integral values from to + including zero. The total number of m values are (2 + 1)

20. Discuss the construction of long form of periodic table. Ans. The elements are arranged in the long form of the periodic table in the increasing order of atomic numbers. Nelis Bohr constructed the long form of the periodic table based on electronic configuration of elements. The important features of the long form of the periodic table are:

Principal quantum

number

Azunythakl

quantum number

Number of symbol

Sub shells

(n) ( )

1 0 S 1(1s)

2 0 1

S P

2(2s, 2p)

3 0 1 2

S P D

3(3s, 3p, 3d)

4

0 1 2 3

S P D f

4(4s, 4p, 4d, 4f)

Sub Shell

value M value - to 0 to +

No. of orbitals 2 + 1

S

P

d f

0

1

2

3

0

-1, 0, +1

-2, -1, 0, +1, +2

-3, -2, -1, 0, +1, +2, +3

1

3

5

7





Cao

Sodium benzoate Benzene

Red hot Cu 600

It consists seven horizontal rows called periods and 18 vertical columns which are classified into 16 groups only. Periods: Every period starts with an alkali metal and ends with an inert gas. The first period consists to two elements only (H, He) and is called very short period. Second period consists 8 elements (Li to Ne) and is called first short period. The third period consists (Na to Ar) 8 elements and is called second short period. Fourth period contains 18 elements (K to Kr) and is called first long period. Fifth period is the second long period with 18 elements (Rb to Xe).

Sixth period is the longest period with 32 elements which starts with Cs and ends with Rn. This

period includes 14 lanthanides. Seventh period is an incomplete period with 20 radioactive elements. Groups: There are 16 groups in the long form of the periodic table (in transition elements three vertical columns are fused and designated as VIII group). These groups are IA, IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA, VA, VIA, VIIA and zero group. The elements of IA, IIA, IIIA, IVA, VA, VIA, VIIA groups are called representative elements or normal elements. Elements of IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIII groups have their ultimate and penultimate shell incomplete. These are called transition elements. IIB elements have (n - 1) d10 nS2 outermost electronic configuration. Zero group elements have stable electronic configuration. These elements are called inert gases, noble gases. These elements have been grouped at the extreme right of the periodic table. In this long periods have been expanded and short periods are broken to accommodate the transitional elements in the middle of the long period. Lanthanides and actinides have been grouped separately and placed at the bottom of the periodic table. 21. Describe any two methods of preparation of Benzene. Explain ay four electrophilic substitution reactions of benzene. Ans. Preparation of Benzene: 1. When Sodium benzoate distilled with Sodalime, Benzene is formed. C6H5COONa + NaOH C6H6 + Na2CO3

2. Polymerization of Acetylene: When Acetylene gas is passed through red hot Cu or Fe tubes, it polymerizes and gives Benzene.

3C2H2 C5H6

1) Halogenation: Benzene reacts with bromine or chlorine in the prescence of Lewis acids like Fecl3, AlCl3 etc, to give corresponding halo benzene





Fe Cl2

25

Nitration mixture < 60

H2SO4/SO3

SO3H

NO2

Anhydrous AZCZ3

Alkyl benzene

+ HCZ RCZ +

e.g.

Similarly with bromine, bromobenzene is formed.

2) Nitration: Benzene undergoes nitration when heated with a mixture of 1:1 (by volume) concentrated nitric acid and concentrated Sulphuric acid (nitration mixture) at a temperature below 60

3) Benzene reacts with fuming Sulphuric acid (oleum) and gives benzene sulphonic acid.

4) Friedal Crafts alkylation and acylation: Benzene reacts with alkyl halides and acyl h in the presence of Lewis acids (AZCZ3, Fecz3) and gives alkyl benzenes and acyl benzenes.

+ Cl2

Cl

+ HCl

Chloro benzene





Anhydrous AZCZ3 + RCOX + HX

Chloronium ion (electrophile)

Benzene reacts with acetyl chloride in the prescence of anhydrous aluminium, chloride and acetophenone.

General Mechanisms: Electrophillic substitution reaction (SE) proceeds in two steps as 1. Generation of electrophile II a) Formation of carbocation intermediate b) Removal of proton from carbocation intermediate.

1.Generation of electrophile E+: In the reactions halogenations, alkylation and acylatio benzene, anhydrous

AZCZ3, the Lewis acid produces electrophile X+ say cZ

+, R

+ and RCO

+ by reacting the reagent chlorine, alkyl

halide and acylhalide respectively.

e.g: CZ CZ + AZCZ3 CZ + [AZCZ4]

II a) Formation of carbocation: Electrophile generated above attacks one of the benz carbons to change it to SP3 hybridised. The carbocation (Arrhenium ion) is stabilized through resonal.





+ [AZCZ4] H

E

H

+ HCZ + AZCZ3

E

Sigma complex loses aromatic character due to delocalization of electrons stopping at SP3 carb.

b) Losing of Proton: To regain aromatic character the C+ loses one proton to SP

3 carbon on attack of (AZCZ4)

-

in case of halogenations, alkylation and aclyation and HSO in case of nitration.





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