1 Haloalkanes and Haloarenes
Which major product is formed in the free-radical bromination of methane by limited supply of bromine?
1) Bromomethane
2) Dibromomethane 3) Tribromomethane 4) Tetra bromomethane
CH4 + Br2 --freeradical−→CH3−Br
Free Radical Mechanism
CH3−H→CH?3+H?
Br−Br→Br?+Br?
⇒CH?3+Br?→CH3−Br (bromomehane)
H?+Br?→ H−Br
⇒ Bromomethane is mojor product.
2 States of Matter
By what factor does the average velocity of a gaseous molecule increase when the temperature (in Kelvin) is doubled? 1) 2.8 2) 4.0 3) 1.4 4) 2.0
SOLUTION:
Average velocity =
3 Chemical Bonding and Molecular Structure
Ortho-Nitrophenol is less soluble in water than p- and m- Nitrophenols because: 1) o-Nitrophenol is more volatile steam than those of m- and p-isomers. 2) o-Nitrophenol shows intramolecular H-bonding 3) o-Nitrophenol shows intermolecular H-bonding 4) Melting point of o-Nitrophenol is lower than those of m- and p-isomers.
SOLUTION
4 States of Matter
Equal masses of methane and oxygen are mixed in an empty container at 25°C. The fraction of the total pressure exerted by oxygen is 1) 1/2 2) 2/3 3) (1/3) ×(273/298) 4) 1/3
let m be the mass of methane and oxygen Number of moles of oxygen=m/32 Number of moles of methane=m/16 Mole fraction of oxygen
Let total pressure be P and Po be partial pressure of Oxygen then Po=XoP Po/P=Xo=(1/3)
5 Aldehydes Ketones and Carboxylic Acids
In the Reaction the product C is
1) acetaldehyde 2) acetylene 3) ethylene 4) acetyl chloride
SOLUTIONS
6 Coordination Compounds
Nickel (Z = 28) combines with a uninegative monodentate ligand X - to form a paramagnetic complex [NiX4]2- . The number of unpaired electron(s) in the nickel and geometry of this complex ion are respectively
1) one, tetrahedral 2) two, tetrahedral 3) one, square planar 4) two, square planar
Hence Nickel has 2 unpaired electrons and the geometry of the complex [Ni X4 ]2- is tetrahedral due to SP3 hybridization.
7 Chemical Kinetics
A chemist prepares 1.00 g of pure $$_{6}^{11}{C}$$. This isotope has half-life of 21 min, decaying by equation: $$_{6}^{11}{C} \longrightarrow _{5}^{11}{B}+_{1}^{0}{e}$$ What is rate of disintegration per second (dps) at start? 1) 3×1019 dps 2) 4×1019 dps 3) 6×1019 dps 4) None
$$\displaystyle -\frac{dN}{dt}=\lambda N_0$$ where $$\lambda$$(disintegration constant) $$\displaystyle = \frac{0.693}{T_{50}}$$ and $$N_0$$ the number of atoms present initially $$\displaystyle N_0=\frac{weight}{atomic\quad weight}\times Avogadro's\quad number$$ $$\displaystyle -\frac{dN}{dt}=\frac{0.693}{21\times 60}\times \frac{1}{11}\times 6.02\times 10^{23}$$ dps $$=3\times 10^{19}$$ dps
8 Electrochemistry
The minimum voltage needed to carry out electrolysis in the reaction is
(F= 96500 Cmol-1)
1) 2.14 2) 4.28 3) 6.42 4) 8.56
9 Chemical Kinetics
A catalyst in the finely divided state is more efficient because in this state
1) it can react with one of the reactant more efficiently
2) it has larger activation energy
3) it has large surface area
4) all of the above
10 Haloalkanes and Haloarenes
Fluorobenzene (C6H5F) can be synthesized in the laboratory
1) by direct fluorination of benzene with F2 gas 2) by reacting bromobenzene with NaF solution 3) by heating phenol with HF and KF 4) from aniline by diazotisation followed by heating the diazonium salt with HBF4
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