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Alcohols, Phenols, and Ethers — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryAlcohols, Phenols, and Ethers4 Marks
Question
Read the passage given below and answer the following questions: Due to intermolecular hydrogen bonding, the boiling points of alcohols and phenols are much higher than those of corresponding haloalkanes, haloarenes, aliphatic and aromatic hydrocarbons. Among isomeric alcohols, the boiling points follow the order: primary > secondary > tertiary. Boiling points of ethers are much lower than those of isomeric alcohols. The solubility of alcohols in water decreases as the molecular mass of alcohols increases. Amongst isomeric alcohols solubility increases with branching. The solubility of phenols in water is much lower than that of alcohols. Lower ethers such as dimethyl ether and ethyl methyl ether are soluble in water, but the solubility decreases as the molecular mass increases. In these questions (Q. No. i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: Alcohols have higher boiling points than ethers of comparable molecular masses.
Reason: Alcohols and ethers are isomeric in nature.
  1. Assertion: The solubility of phenols in water is much lower than that of alcohols.
Reason: Phenols do not form H-bonds with water.
  1. Assertion: Among n-butane, ethoxyethane, 1-propanol and 2-propanol, the increasing order of boiling points is, 1-butanol < 1-propanol < ethoxyethane < n-butane.
Reason: Boiling point increases with increase in molecular mass.
  1. Assertion: Dimethyl ether and diethylether are soluble in water.
Reason: As the molecular mass increases, solubility of ethers in water decreases.
  1. Assertion: Butan-2-ol has higher boiling point than 2-methylpropan-2-ol.
Reason: Amongst isomeric alcohols, the boiling points decreases with branching.
✓

Answer

  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
Explanation:
Due to the presence of intermolecular H-bondi ng in alcohols, they have higher boiling points than isomeric ethers.
  1. (c) Assertion is correct statement but reason is wrong statement.
​​​​​​​Explanation:
Like alcohols, phenols also form H-bond with water. But the solubility of phenols in water is much lower than that of alcohols because of the larger non-polar hydrocarbon part (benzene ring) present in their molecules.
  1. (d) Assertion is wrong statement but reason is correct statement.
​​​​​​​​​​​​​​​​​​​​​Explanation:
Boiling point increases with increase in molecular mass so, 1-butanol has higher boiling point than 1-propanol. Ethers do not form hydrogen bonds thus, they have lower boiling points than the corresponding alcohols.
Due to weak dipole-dipole interactions, the boiling points of lower ethers are only slightly higher than those of the n-alkanes having comparable molecular masses,
Thus, the increasing order of boiling points is n-butane < ethoxyethane < 1-propanol < l-butanol.
  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:
The solubility of lower ethers in water is due to the formation of H-bonds between water and ether molecules. As the molecular mass increases, the solubility of ethers in water decreases due to corresponding increase in the hydrocarbon portion of the molecule.
  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

Amongst isomeric alcohols,the boiling points decrease with branching due to a corresponding decrease in surface area.

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Read the passage given below and answer the following questions:
At $298 K,$ the vapour pressure of pure benzene $, C_6, H_6$ is $0.256$ bar and the vapour pressure of pure toluene $\ce{C_6 H_5 CH_3}$ is $0.0925$ bar. Two mixtures were prepared as follows:
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  2. $3.9g$ of $\ce{C_6 H_6 + 13.8g}$ of toluene
The following questions are multiple choice questions. Choose the most appropriate answer:
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  1. $0.128$
  2. $0.174$
  3. $0.198$
  4. $0.258$
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  1. $I$
  2. $II$
  3. Both have equal vapour pressure
  4. Cannot be predicted
  1. Mole fraction of benzene in vapour phase in solution I is.
  1. $0.128$
  2. $0.174$
  3. $0.734$
  4. $0.266$
  1. Which of the following statements is/are correct?
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  2. Mole fraction of toluene in vapour phase is less in solution $I.$
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  2. Only $I$
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  1. $VO$
  2. $V_2O_3$
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  2. $+7$
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Read the passage given below and answer the following questions:
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The following questions are multiple choice questions. Choose the most appropriate answer:
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  1. Methyl amine.
  2. Tri methyl amine.
  3. Aniline.
  4. Dimethyl amine.
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  4. $\ce{(CH_3)_3N > CH_3NH_2 > (CH_3)_2NH}$
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  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
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  4. Assertion is wrong statement but reason is correct statement.
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Read the passage given below and answer the following questions:
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The following questions are multiple choice questions. Choose the most appropriate answer:
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  2. $2-$ Butanol
  3. $2-$ Methyl $-1-$ propanol
  4. $2-$ Methyl $-2-$ propanol
  1. The carbonyl compound producing an optically active product by reaction with $\ce{LiAlH}_4$ is:
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  1. $\ce{CH_3CH_2CH_2CH_2OH}$
  2. $\ce{CH_3CH(OH)CH_2CH_3}$
  3. $\ce{(CH_3)_3COH}$
  4. $\ce{CH_3CH_{2 }- O - CH_2CH_3}$
  1. In the oxidation of  by acidified $\ce{K_2Cr_2O_7},$ the products are:
  1. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\\\text{CH}_3-\ ^\text{14}\text{C}-\text{OH}$ and $\text{CH}_3\text{CH}_2\text{COOH}$
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  4. None of these.
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  3. $\frac{\text{H}_2}{\text{Ni}}$
  4. $\text{AICl}_3$
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Read the passage given below and answer the following questions: Ligands are atoms or ions which can donate electrons to the central atoms. Ligands can be monodentate, bidentate or polydentate as well. Few ligands can coordinate with the central atom through more than one site, these are called ambidentate ligands. When a di- or polydentate ligand uses its two or more donor atoms to bind a single metal ion, it is said to be a chelating ligand. In these questions $(Q. No. i-iv),$ a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Assertion: Glycinate ion is an example of monodentate ligand.
Reason: Glycinate contains $N $ and $O$ as donor atoms.
  1. Assertion: $EDTA$ forms complex with divalent metals of 3d-series in the ratio of $1 : 1.$
Reason: $EDTA$ has $4 - COOH$ groups.
  1. Assertion: Oxalate ion is a bidentate ligan.
Reason: Oxalate ion has two donor atoms.
  1. Assertion: A chelating ligand must possess two or more lone pairs at such a distance that it may form suitable strain free $5 $ and $6$ membered rings with the metal ion.
Reason: $H_2N - NH_2$ is a chelating ligand.
  1. Assertion: In Zeise's salt coordination number of $Pt$ is five.
Reason: Ethene is a monodentate ligand.
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Decrease in concentration of reactant or increase in concentration of product per unit time is called rate of reaction. lt is of two types :
  1. Instantaneous rate of reaction : Rate of change of concentration of reactant or product at a particular time is called instantaneous rate of reaction.
$\text{r}_\text{inst.}=\frac{\text{dC}}{\text{dt}}$
where$, dC =$ infinitely small change in concentration
$dt =$ infinitely small change in time.
  1. Average rate of reaction : Ratio of change in concentration and time required for the change is average rate of reaction.
$\text{r}_\text{av}=\frac{\triangle\text{x}}{\triangle\text{t}}=\frac{\text{Change in concentration}}{\text{Time required for the change}}$
For a reaction of the type$, m_1A + m_2B \rightarrow n_1C + n_2D$
Rate of reaction is given as
$\frac{1}{\text{m}_1}\frac{\text{d[A]}}{\text{dt}}=-\frac{1}{\text{m}_2}\frac{\text{d[B]}}{\text{dt}}=+\frac{1}{\text{n}_1}\frac{\text{d[C]}}{\text{dt}}=+\frac{1}{\text{n}_2}\frac{\text{d[D]}}{\text{dt}}$
In these questions $(Q.$ No. $i-iv),$ a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: The kinetics of the reaction, $\text{mA}+\text{nB}+\text{pC}\rightarrow\text{m}'\text{ X}+\text{n}'\text{ Y}+\text{p}'\text{ Z}$ obey the rate expression as $\frac{\text{dx}}{\text{dt}}=\text{k}[\text{A}]^\text{m}[\text{B}]^\text{n}.$
Reason: The rate of the reaction does not depend upon the concentration of $C$.
  1. Assertion : Instantaneous rate of reaction is equal to $\frac{\text{dx}}{\text{dt}}.$
Reason : lt is the rate of reaction at any particular instant of time.
  1. Assertion : For the reaction, $\text{RCl}+\text{NaOH}\rightarrow\text{ROH}+\text{NaCl},$ the rate of reaction is reduced to half on reducing the concentration of $\ce{RCl}$ to half.
Reason : The rate of reaction is represented by $\ce{k[RCl}].$
  1. Assertion : ln rate law, unlike in the expression for equilibrium constants, the exponents for concentrations do not necessarily match the stoichiometric coefficients.
Reason: It is the mechanism and not the balanced chemical equation for the overall change that governs the reaction rate.
  1. Assertion : ln a reaction$, 2A + B \rightarrow A_2B,$ the reactant $B$ will disappear at twice the rate as $A$ will decrease.
Reason: The rate of disappearance of reactant will be $-\frac{1}{2}\frac{\text{d[A]}}{\text{dt}}=-\frac{\text{d[B]}}{\text{dt}}$
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