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Chemistry 1 Marks Question

Hydrocarbons · MP Board (MPBSE) STD 11 Science (Madhya Pradesh - English Medium). 75 questions.

Questions · Page 2 of 2

1 Marks Question

Question 511 Mark
Name the reagent used in the following changes
$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{C}\equiv\text{C}-\text{CH}_2-\text{CH}_2-\text{CH}_2\\-\text{CH}_3\xrightarrow{?}\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\\\text{C}=\text{C}-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_3\\ \ | \ \ \ \ \ \ \ |\\ \text{H} \ \ \ \ \ \text{H}$
Answer
$\mathrm{H}_2 / \mathrm{Pd}-\mathrm{BaSO}_4$ is used. It is called Lindlar's catalyst. Syn addition takes place i.e., both hydrogen atom attack from same side.
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Question 521 Mark
Why eclipsed and staggered forms of ethane cannot be isolated at room temperature?
Answer
It is because the difference in their energy is less. They can interchange into each other easily, therefore, their isolation (separation) is not possible.
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Question 531 Mark
The intermediate carbocation formed in the reactions of $\mathrm{HI}, \mathrm{HBr}$ and HCl with propene is the same and the bond energy of $\mathrm{HCl}, \mathrm{HBr}$ and HI is $430.5 \mathrm{~kJ} \mathrm{~mol}^{-1}, 363.7 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $296.8 \mathrm{~kJ} \mathrm{~mol}^{-1}$ respectively. What will be the order of reactivity of these halogen acids?
Answer
Hydrogen halides $(\mathrm{HCl}, \mathrm{HBr}, \mathrm{HI})$ add up to a alkanes to form alkyl halides. The order of reactivity of the hydrogen halides is $\mathrm{HI}>\mathrm{HBr}>\mathrm{HCl}$. Reactivity of HX depends on bond dissociation enthalpy of HX . Bond enthalpy of HI ( $\left.296.8 \mathrm{kj} \mathrm{~mol}^{-1}\right)<\mathrm{HBr}\left(363.7 \mathrm{kj} \mathrm{~mol}^{-1}\right)<\mathrm{HCl}\left(430 \mathrm{kj} \mathrm{~mol}^{-1}\right)$ is in this order hence the reactivity is in reverse order:
$\text{HCl} < \text{HBr} < \text{HI}$
$\text{CH}_3-\text{CH}=\text{CH}_2+\text{H}^+$ slow step $\rightarrow\text{CH}_{3^-}\ ^+\text{CH}-\text{CH}_3+\text{X}^-\text{fast}\ \rightarrow\text{H}_3-\text{CHX}-\text{CH}_3$
Slow step is rate determining step and it depends on the availability of $\mathrm{H}^{+}$. Availability of $\mathrm{H}^{+}$depends on bond dissociation enthalpy of HX .
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Question 551 Mark
Bring out the following conversion ethane to ethene.
Answer
$\text{CH}_3\text{CH}_3\xrightarrow[-\text{HI}]{\text{I}_2/\text{HNO}_3}\text{CH}_3\text{CH}_2\text{I}\xrightarrow{\text{KOH(alc.)}}\text{CH}_2=\text{CH}_2\\ \ \ _{\text{Ethane}} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ _{\text{Ethyl iodide}} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ _{\text{Ethene}}$
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Question 571 Mark
Why is addition reaction of bromine to benzene difficult?
Answer
Addition reaction of bromine to benzene is difficult due to delocalisation of $\pi-$electrons. It does not have pure double bonds and does not give test for unsaturation.
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Question 581 Mark
Convert methane into ethane.
Answer
$\text{CH}_4\xrightarrow[\text{UV light}]{\text{Cl}_2}\text{CH}_3\text{Cl}\xrightarrow[\text{Dry ether}]{2\text{Na}}\text{CH}_3-\text{CH}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ _{\text{Ethane}}$
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Question 591 Mark
Why has trans-isomer higher melting point than cis-isomer?
Answer
Trans-isomer, being symmetrical, can fit into crystal lattice more readily than cis-form, therefore, it has higher melting point due to stronger forces of attraction.
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Question 611 Mark
n-propylmagnesium bromide on hydrolysis gives propane. Is there any other Grignard reagent which also gives propane? If so, give its name, structure and equation for the reaction.
Answer
Iso-propylmagnesium bromide, $\left(\mathrm{CH}_3\right)_2 \mathrm{CHMgBr}_{,}\left(\mathrm{CH}_3\right)_2 \mathrm{CHMgBr}+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_3+\mathrm{Mg}(\mathrm{OH}) \mathrm{Br}$
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Question 621 Mark
How would you distinguish between:
  1. But$-1-$yne and but$-2-$yne.
  2. Propene and propyne.
Answer
  1. Upon treatment with ammoniacal solution of $\mathrm{AgNO}_3$. But$-1-$yne would give white ppt whereas but$-2-$yne does not react.
  2. Upon treatment with ammoniacal solution of $\mathrm{AgNO}_3$. propyne would give white ppt. whereas propene does not react.
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Question 641 Mark
Give an alkyne which produces acetic acid and propanoic acid on treatment with alkaline $\mathrm{KMnO}_4$ at $100^{\circ} \mathrm{C}$.
Answer
$\text{CH}_3-\text{C}\equiv\text{C}-\text{CH}_2-\text{CH}_3\xrightarrow[100^\circ]{\text{KMnO}_4/\text{KOH}}\\\ \ \ \ \ _\text{Pent-2-yne}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\\\text{CH}_3-\text{C}-\text{OH}\\ \ \ \ \ _{\text{Ethanoic acid}}\\\text{CH}_3\text{CH}_2\text{COOH}\\ \ \ \ \ _{\text{Propanoic acid}}$
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Question 651 Mark
Complete the reaction $\text{CH}_3-\text{CH}=\text{CH}_2+\text{HCl}\xrightarrow{\text{Peroxide}}$
Answer
$\text{CH}_3-\text{CH}=\text{CH}_2+\text{HCl}\xrightarrow{\text{Peroxide}}\text{CH}_3-\text{CH}-\text{CH}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Cl}$
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Question 661 Mark
Which type of isomerism is present in $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH}$ and $\mathrm{CH}_3 \mathrm{OCH}_3$?
Answer
Functional isomerism because they have same molecular formula but different functional groups.
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Question 681 Mark
Why do hydrocarbon molecules with an odd number of carbon atoms have lower melting points than those with an even number of carbon atoms?
Answer
Molecules with odd number of carbon atoms have lower melting points because they do not fit into crystal lattice easily whereas, hydrocarbons with even number of carbon atoms can fit into crystal lattice easily and more energy is needed to melt them, hence, have higher melting point.
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Question 691 Mark
How many secondary carbons are there in 2, 2-dimethylbutane?
Answer
$\ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\stackrel{{1^\circ}}{\hbox{ CH}}_3-\stackrel{{4^\circ}}{\hbox{C}}-\stackrel{{2^\circ}}{\hbox{ CH}}_2-\stackrel{{1^\circ}}{\hbox{ CH}}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$ has one 2° (secondary)carbon.There are four primary carbon, one 4° carbon.
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Question 701 Mark
Give the structural formula of 5-sec butyl-4-iso propyl decane.
Answer
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}-\text{CH}-\text{CH}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\stackrel{{1}}{ \ \hbox{ CH}}_3-\stackrel{{2}}{ \ \hbox{ CH}}_2-\stackrel{{3}}{ \ \hbox{ CH}}_2-\stackrel{{4}}{ \ \hbox{ CH}}-\stackrel{{5}}{ \ \hbox{ CH}}-\stackrel{{6}}{ \ \hbox{ CH}}_2-\stackrel{{7}}{ \ \hbox{ CH}}_2-\stackrel{{8}}{ \ \hbox{ CH}}_2-\stackrel{{9}}{ \ \hbox{ CH}}_2-\stackrel{{10}}{ \ \hbox{ CH}}_3\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3-\text{CH}-\text{CH}_2-\text{CH}_3$
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Question 721 Mark
How can we obtain isobutane from n-butane?
Answer
Isobutane can be obtained by heating n-butane with $\mathrm{AlCl}_3$ by isomerisation reaction. $\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3\xrightarrow[\text{heat}]{\text{AlCl}_3}\text{CH}_3-\text{CH}-\text{CH}_3\\\ \ \ \ \ \ \ \ \ \ _\text{n-Butane} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ _\text{Isobutane}$
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Question 741 Mark
Why does cis-2-butene have a higher boiling point than trans-2-butene?
Answer
cis-2-Butene is more polar than trans-2-butene, therefore, it has more van der Waals’ forces of attraction, hence higher boiling point due to higher dipole moment, whereas trans-2-butene has zero dipole moment.
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Question 751 Mark
How will you detect the presence of unsaturation in an organic compound?
Answer
Add bromine water. If it gets decolourised, compound is unsaturated. e.g., Ethene and Ethyne decolourise bromine water because these are unsaturated having double and triple bond respectively.
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1 Marks Question - Page 2 - Chemistry STD 11 Science Questions - Vidyadip