imp questions in hydrocarbons
Answers
Explanation:
They are hydrophobic and dissolve in nonpolar or weakly polar solvents.
They are less dense than water.
The boiling point of alkane increases by 20-30 degree Celsius with each additional methylene group.
For isomeric alkanes, the boiling point decreases with branching due to an overall increase in surface area.
WBJEE: Important Questions and Preparation Tips –Periodic Classification & Periodicity in Properties
Physical properties of Alkynes:
It follows the same trend of alkenes and alkanes.
First three members of alkenes are gases, the next eight are liquids and the higher ones are solids.
They are colourless.
Except Ethyene all other members of alkenes are odourless.
They are weakly polar in nature.
They are immiscible with water but soluble in organic solvents like ethers, carbon tetrachloride and benzene.
With increase in molar mass their melting point, boiling point and density also increase.
Some previous years’ solved questions are given below:
Question 1:
From the following compounds choose the one which is not aromatic:
Solution 1:
This compound is cyclooctatetraene which is non polar. Hence this is non aromatic compound.
Hence, the correct option is (B).
Question 2:
Ozonolysis of an alkene produces only one dicarbonyl compound. The structure of the alkene is:
Solution 2:
Hence, the correct option is (B).
Question 3:
The major products obtained during ozonolysis of 2, 3 – dimethyl-1-butene and subsequent reductions with Zn and H2O are
(A) Methanoic acid and 2-methyl-2-butanone
(B) Methanal and 3-methyl-2-butanone
(C) Methanol and 2,2-dimethyl-3-butanone
(D) Methanoic acid and 2-methyl-3-butanone
Solution 3:
The chemical reaction can be shown as below:
Hence, the correct option is (B).
Question 4:
Choose the correct statements(s) among the following:
Solution 4:
So, they are not enantiomers.
Hence, the correct options are (B) and (D).
You can also have a look on the following questions and solutions to check your preparation.
Question 1:
Provide an acceptable name for the alkane shown below:
(A) 6–ethyl–2–methyl–5–propyldecane
(B) 5–ethyl–6–methyl–2–propyldecane
(C) 2–ethyl–6–methyl–2–propyldecane
(D) 2–ethyl–6–methyl–5–propyldecane
Solution 1:
The name of the given compound is 6–ethyl–2–methyl–5–propyldecane.
Hence, the correct option is (A).
Question 2:
Which of the following compounds will exhibit geometrical isomerism?
(A) 1–Phenyl–2–butane
(B) 3–Phenyl–1–butene
(C) 2–Phenyl–1–butene
(D) 1,1–Diphenyl–1–propene
Solution 2:
The compound 1–Phenyl–2–butane will exhibit geometrical isomerism.
Hence, the correct option is (A).
Question 3:
Provide the systematic name of the compound shown:
(A) 4 – butyl – 1 – ethyl – 2 – methylcycloheptane
(B) 4 – butyl – 2 – ethyl – 1 – methylcycloheptane
(C) 1 – butyl – 4 – ethyl – 3 – methylcycloheptane
(D) 2 – butyl – 4 – ethyl – 1 – methylcycloheptane
Solution 3:
Naming according to closest set of locant rule is 4 – butyl – 1 – ethyl – 2 – methylcycloheptane.
Hence, the correct option is (A).
Question 4:
Which of the following compounds is insoluble even in hot concentrated H2SO4?
(A) Ethylene (B) Benzene
(C) Hexane (D) Aniline
Solution 4:
Hexane is insoluble even in hot concentrated H2SO4.
Hence, the correct option is (C).
Question 5:
The number of possible alkynes with molecular formula C5H8 is
(A) 1
(B) 3
(C) 5
(D) 8
Solution 5:
Hence, the correct option is (B).
Conclusion:
All the concepts related to Hydrocarbons like properties, physical properties and chemical properties are presented in a systematic manner which will help students in understanding this topic easily. Students can easily predict the difficulty level of the questions which can be asked in WBJEE 2018 with the help of previous years’ solved questions given here. Students can also track their progress after attempting the questions given here.
Important Questions and Preparation Tips –