Hydrocarbons Test

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Hydrocarbons Test - 52

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Weekly Quiz Competition

Question 1
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Which is not obtained when metal carbides react with $$H_{2}O$$?

A
$$Al_{4}C_{3}+H_{2}O\longrightarrow CH \equiv CH$$

B
$$CaC_{2}+H_{2}O\longrightarrow CH \equiv CH$$

C
$$Mg_{4}C_{3}+H_{2}O\longrightarrow CH_{3}C \equiv CH$$

D
$$Be_{2}C+H_{2}O\longrightarrow CH_{4}$$

Solution

Balanced reactions are:
$$Be_2 C +4H_2O \rightarrow 2Be(OH)_2 +CH_4 $$
$$CaC_2+ 2H_2 O \rightarrow Ca(OH)_2 +C_2H_2$$
$$Mg_{4}C_{3}+H_{2}O\longrightarrow CH_{3}C \equiv CH$$
$$Al_4C_3+12H_2O\rightarrow 4Al(OH)_3+3CH_4$$
Question 2
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Directions For Questions

The term carbide is generally applied to compounds in which carbon is bonded to the elements of lower or approximately same electronegativity. This definition excludes the compounds in which oxygen, sulphur, phosphorus, nitrogen, and halogens are united with carbon. Reactive metals (i.e., of groups 1 and 2) form ionic carbides. They hydrolyze to liberate hydrocarbons. Most of them resemble with $$NaCl$$ in the crystal structure. Transition metals form interstitial carbides.

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Consider the following carbides:
$$\underset {I}{CaC_2} {\;} \underset {II}{Be_2C} {\;} \underset {III}{MgC_2} {\;} \underset {IV}{SrC_2}$$
Select the carbide which gives different product on hydrolysis than other carbides.

A
I

B
II

C
III

D
IV

Solution

CaC2 + 2 H2O----------->C2H2 + Ca(OH)2

Be2C + 4 H2O ----------->2 Be(OH)2 + CH4

MgC2 + 2 H2O ------->Mg(OH)2 + C2H2

$$SrC_2+H2O\rightarrow Sr(OH)_2+C_2H_2$$

So only option B will give a different product.

Hence option B is correct.
Question 3
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Which is not obtained when metal carbides react with $$H_2O$$?

A
$$Al_{ 4 }C_{ 3 }+H_{ 2 }O\rightarrow CH\equiv CH$$

B
$$CaC_2 +H_{ 2 }O\rightarrow CH\equiv CH$$

C
$$Mg_4C_3 +H_{ 2 }O\rightarrow CH_3C\equiv CH$$

D
$$Be_2C + H_2O \rightarrow CH_4$$

Solution

$$Al_{ 4 }C_{ 3 }+H_{ 2 }O\rightarrow 4Al(OH)_3 + CH_4$$
Thus alkane is formed instead of acetylene. Thus option A is incorrect.
Question 4
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Which of these metal carbides on reaction with $$H_2O$$ form $$CH_4$$?

A
$$CaC_2$$

B
$$Mg_3C_2$$

C
$$Be_2C$$

D
$$SiC$$

Solution

$$Be_2C(s) + 4H_2O(l) \rightarrow 2Be(OH)_2(s) + CH_4(g)$$
$$CaC_2 + 2H_2O \rightarrow C_2H_2 + Ca(OH)_2$$
$$Mg_3C_2 + 4H_2O \rightarrow 2Mg (OH)_2+ C_3H_4$$
Question 5
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Consider two alternative mechanisms for the chlorination of methane, Which step is crucial in deciding which mechanism is not likely to be observed?
Mechanism I:
$$A.\ \:Cl_{2} \rightarrow 2 Cl ^{*}$$
$$B. \ \:Cl^{*}+CH_{4} \rightarrow HCl+^{*}CH_{3}$$
$$C. \ \:\dot{C}H_{3}+Cl_{2} \rightarrow CH_{3} Cl+Cl^{*}$$
Mechanism II:
$$D.\ \:Cl_{2} \rightarrow 2 Cl ^{*}$$
$$E. \ \:Cl^{*}+CH_{4} \rightarrow CH_{3}Cl+H ^{*}$$
$$F. \ \:H^{*}+Cl_{2} \rightarrow HCl+Cl^{*}$$

A
$$I$$

B
$$II$$

C
$$I$$ and $$II$$ both

D
None

Solution

In chlorination of methane in presence of sunlight is the free radical mechanism where chain elongation step is rate determining step. For that formation of $$Cl^{*}$$ free radical is crucial.
Chain elongation process-
$$Cl_2+CH_{3}^{*} \rightarrow CH_3Cl+Cl^{*}$$
Question 6
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What are the numerical values of N and M?

A
6,6

B
5,4

C
4,4

D
3,3

Solution

The four possibilities for two chlorines in $$C_3H_6Cl_2$$ is for the Cl's to be 1,1, 2,2, 1,2, or 1,3.
i.e. 1,1-dichloropropane, 2,2-dichloropropane, 1,2-dichloropropane, and 1,3-dichloropropane.
Question 7
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Which of the following pairs of compounds of carbon will undergo combustion as well as addition reaction?

A
$$CH_4$$ and $$C_2H_6$$

B
$$C_2H_6O$$ and $$C_3H_8O$$

C
$$C_2H_4O_2$$ and $$C_3H_6O$$

D
$$C_2H_2$$ and $$C_3H_6$$

Solution

Both $$C_2H_2$$ (ethyne) and $$C_3H_6$$ (propene) are unsaturated hydrocarbons. Hence, they would undergo both combustion and addition reactions.
$$\displaystyle{C_2H_2 + \frac{5}{2}O_2 \rightarrow 2CO_2 + H_2O}$$

$$\displaystyle{C_3H_6 + \frac{9}{2}O_2 \rightarrow 3CO_2 + 3H_2O}$$
$$\underset{ethyne}{C_2H_2} + 2H_2 \rightarrow \underset{ethane}{C_2H_6}$$
$$\underset{propene}{C_3H_6} + H_2 \rightarrow \underset{propane}{C_3H_8}$$
$$CH_4$$ and $$C_2H_6$$ are saturated hydrocarbons and do not undergo addition reactions. $$C_2H_6O$$ and $$C_3H_8O$$ are ethanol and propanol, respectively, and do not undergo addition reactions. $$C_2H_4O_2$$ and $$C_3H_6O$$ are ethanoic acid and acetone, respectively. They cannot undergo both combustion and addition reactions.
Question 8
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With the help of the following equations and data choose the wrong statement.

A
Thermal cracking of (CH) bond of methane occurs at 1500 K and that of (CH) bond of ethane breaks at 800900 K.

B
During homolysis of ethane at high temperature, the (CC) bond breaks more radily than (CH) bonds.

C
During the cracking of n-butane, reaction (IV) occurs more readily than reaction (V).

D
Formation of $$CH_3CH_2$$ radical by reaction (II) will take place at lower temperature than the formation of $$C_2H_5$$ radical by reaction (IV).

Solution

The option (D) represents wrong statement.
Formation of $$CH_3CH_2$$ radical by reaction (II) will take place at lower temperature than the formation of $$C_2H_5 $$radical by reaction (IV).
Question 9
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Which of the following statement(s) is correct?

A
The compound (B) is

B
The compound (B) is

C
The compound (A) on reaction with HI + Red P gives

D
The compound (A) on oxidation with $$MnO_2$$ gives

Solution

$$POCl_3$$ is a dehydrating agent and it removes water molecule from alcohols. The more substituted alkene is formed as the major product. Hence the major product is 1−methylcyclohexene.

Hence, the correct option is $$\text{A}$$
Question 10
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Arrange the reactions given below in proper sequence for the conversion of ethane to methane.
(a) Treatment with sodium hydroxide
(b) Treatment with aqueous $$KOH$$
(c) Treatement with $$NaOH+CaO$$
(d) Halogenation
(e) Reaction with acidified $${K}_{2}{Cr}_{2}{O}_{7}$$

A
$$e\ a\ d\ b\ c$$

B
$$d\ b\ e\ a\ c$$

C
$$e\ c\ b\ a\ d$$

D
$$d\ e\ a\ b\ c$$

Solution

for the conversion of ethane to methane.
(d) Halogenation $$\Rightarrow CH_3-CH_3 \rightarrow CH_3-CH_2-Cl$$
(e) Reaction with acidified $${K}_{2}{Cr}_{2}{O}_{7}$$ $$\Rightarrow CH_3-CH_2Cl \rightarrow CH_3-COOH$$
(a) Treatment with sodium hydroxide$$\Rightarrow CH_3-COOH+ NaOH \rightarrow CH_3-COONa$$
(b) Treatment with aqueous $$KOH$$ $$\Rightarrow CH_3-COONa \rightarrow CH_4(aq)$$
(c) Treatement with $$NaOH+CaO$$ $$\Rightarrow CH_4(aq)\rightarrow CH_4$$