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Haloalkanes and Haloarenes — Chemistry STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceChemistryHaloalkanes and Haloarenes4 Marks
Question

Read the passage given below and answer the following questions:

The aryl halides are relatively less reactive towards nucleophilic substitution reactions as compared to alkyl halides. This low reactivity can be attributed to the following factors:

  • The C - X bond in halobenzene has a partial double bond character due to involvement of halogen electrons in resonance with benzene ring.
  • The C - X bond in aryl halides is less polar as compared to that in alkyl halides as sp2 hyridised carbon is more electronegative than sp3 hybridised carbon.

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: Primary benzylic halides are more reactive than primary alkyl halides towards SN1 reactions.

Reason: Reactivity depends upon the nature of the nucleophile and the solvent.

  1. Assertion: is more reactive than towards nucleophilic substitution reactions.

Reason: Tertiary alkyl halides react predominantly by SN1 mechanism.

  1. Assertion: Chlorobenzene is more reactive than p-chloroanisole to nucleophilic substitution reactions.

Reason: Greater the stability of carbanion, greater is its ease of formation and hence, more reactive is the aryl halide.

  1. Assertion: 4-Nitrochlorobenzene undergoes nucleophilic substitution more readily than chlorobenzene.

Reason: Chlorobenzene undergoes nucleophilic substitution by elimination-addition mechanism while 4-nitrochlorobenzene undergoes nucleophilic substitution by addition-elimination mechanism.

  1. Assertion: Chlorobenzene is less reactive than benzene towards the electrophilic substitution reaction.

Reason: Resonance destabilises the carbocation.

✓

Answer

  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

​​​​​​​​​​​​​​​​​​​​​Explanation:

Primary benzylic halides show higher reactivity in SN1 reactions than primary alkyl halides. This is due to the greater stabilisation of the benzylic carbocation intermediates by resonance.

  1. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

On comparing the relative stabilities of carbanion of chlorobenzene and p-chloroanisole,

The electron donating group (OCH3) in anisole tends to intensify the negative charge relative to carbanion in chlorobenzene. Thus, p-chloroanisole is less reactive than chlorobenzene.

  1. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

As compared to chlorobenzene, the intermediate carbanion resulting from 4-nitrochlorobenzene is stabilized by-R-effect of the N02 group.

  1. (c) Assertion is correct statement but reason is wrong statement.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

Chlorobenzene is less reactive than benzene towards the electrophilic substitution reactions due to -I effect.

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Read the passage given below and answer the following questions:

When a solution of an et-amino acid is placed in an electric field depending on the pH of the medium, following three cases may happen.

  1. In alkaline solution, CL-amino acids exist as anion II, and there is a net migration of amino acid towards the anode.
  2. In acidic solution, a-amino acids exist as cation III, and there is a net migration of amino acid towards the cathode.
  3. If II and III are exactly balanced there is no net migration; under such conditions any one molecule exists as a positive ion and as a negative ion for exactly the same amount of time, and any small movement in the direction of one electrode is subsequently cancelled by an equal movement back toward the other electrode. The pH of the solution in which a particular amino acid does not migrate under the influence of an electric field is called the is oelectric point of that amino acid.

The following questions are multiple choice questions. Choose the most appropriate answer:

  1.  

Arrange in order of increasing acid strengths. 

  1. X > Z > Y
  2. Z < X < Y
  3. X > Y > Z
  4. Z > X > Y
  1. In aqueous solutions, amino acids mostly exist as:
  1. NH2 - CHR - COOH
  2. NH2 - CHR - COO-

  3. $\stackrel{+}{\hbox{ N}}\text{H}_3\text{CHRCOOH}$

  4. $\text{H}_3\stackrel{{+}}{\hbox{N}}\text{CHRCOO}^-$

  1. Amino acids are least soluble:
  1. at pH 1
  2. at pH 7
  3. At their isoelectric points.
  4. None of these.
  1. The $\text{pK}_{\text{a}_1}$ and $\text{pK}_{\text{a}_2}$ of an amino acid are 2.3 and 9.7 respectively. The is oelectric point of the amino acid is:
  1. 12.0
  2. 7.4
  3. 6.0
  4. 3.7
  1. A tripeptide (X) on partial hydrolysis gave two dipeptides Cys-Gly and Glu-Cys. Identify the tripeptide.
  1. Glu-Cys-Gly
  2. Gly-Glu-Cys
  3. Cys-Gly-Glu
  4. Cys-Glu-Gly
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The half-life of a reaction is the time required for the concentration of reactant to decrease by half, i.e.,

$[\text{A}]_\text{t}=\frac{1}{2}[\text{A}]$

For first order reaction,

$\text{t}_\frac{1}{2}=\frac{0.693}{\text{k}}$

this means $\text{t}\frac{1}{2}$ is independent of initial concentration. Figure shows that typical variation of concentration of reactant exhibiting first order kinetics. It may be noted that though the major portion of the first order kinetics may be over in a finite time, but the reaction will never cease as the concentration of reactant will be zero only at infinite time.

The following questions are multiple choice questions. Choose the most appropriate answer:

  1. A first order reaction has a rate constant k = 3.01 × 10-3 /s. How long it will take to decompose half of the reactant?
  1. 2.303s
  2. 23.03s
  3. 230.3s
  4. 2303s
  1. The rate constant for a first order reaction is 7.0 × 10-4 s-1. If initial concentration ofreactant is 0.080 M, what is the half life of reaction?
  1. 990s
  2. 79.2s
  3. 12375s
  4. 10.10 × 10-4s
  1. For the half-life period of a first order reaction, which one of the following statements is generally false?
  1. It is independent of initial concentration.
  2. It is independent of temperature.
  3. It decreases with the introduction of a catalyst.
  4. None of these.
  1. The rate of a first order reaction is 0.04 mol L-1 s-1 at 10 minutes and 0.03 mol L-1 s-1 at 20 minutes after initiation. The half-life of the reaction is:
  1. 4.408 min
  2. 44.086 min
  3. 24.086 min
  4. 2.408 min

  1. The plot of $\text{t}_\frac{1}{2}$ vs initial concentration [A]0 for a first order reaction is given by:

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Explain the structure of nucleic acid compounds.
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For the reaction : $2\text{NO}_\text{(g)}+\text{Cl}_{2\text{(g)}}\rightarrow2\text{NOCl}_\text{(g)},$ the following data were collected. All the measurements were taken at 263K.
Experiment No.
Initial [NO] (M)
Initial [Cl2] (M)
Initial rate of disapp. of Cl2 (M/ min)
1.
0.15
0.15
0.60
2.
0.15
0.30
1.20
3.
0.30
0.15
2.40
4.
0.25
0.25
?
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. The molecularity of the reaction is:
  1. 1
  2. 2
  3. 3
  4. 4
  1. The expression for rate law is:
  1. $\text{r}=\text{k}[\text{NO}][\text{Cl}_2]$
  2. $\text{r}=\text{k}[\text{NO}]^2[\text{Cl}_2]$
  3. $\text{r}=\text{k}[\text{NO}][\text{Cl}_2]^2$
  4. $\text{r}=\text{k}[\text{NO}]^2[\text{Cl}_2]^2$
  1. The overall order of the reaction is:
  1. 2
  2. 0
  3. 1
  4. 3
  1. The value of rate constant is:
  1. 150.32 M-2 min-1
  2. 200.08 M-1 min-1
  3. 177.77 M-2 min-1
  4. 155.75 M-1 min-1
  1. The initial rate of disappearance of Cl2 in experiment 4 is:
  1. 1.75M min-1
  2. 3.23M min-1
  3. 2.25M min-1
  4. 2.77M min-1
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Read the passage given below and answer the following questions:

Reimer-Tiemann reaction introduces an aldehyde group, on aromatic ring of phenol, ortho to the hydroxyl group. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.

The following questions are multiple choice questions. Choose the most appropriate answer:

  1. Reimer-Tiemann reaction is an example of:
  1. Nucleophilic substitution reaction.
  2. Electrophilic substitution reaction.
  3. Nucleophilic addition reaction.
  4. Electrophilic addition reaction.
  1. Which of the following reagents is used in the given reaction in steps I?
  1. aq. NaOH + CH3Cl
  2. aq. NaOH + CH2Cl2
  3. aq. NaOH + CHCl3
  4. aq. NaOH + CCl4
  1. The electrophile in this reaction (A) is:
  1. : CHCI
  2. +CHCl2
  3. : CCl2
  4. .CCl3
  1. The structure of the intermediate (A) is:

  1. When phenol reacts with chloroform in presence of KOH, the product formed is:
  1. Salicylic acid.
  2. Salicylaldehyde.
  3. Both (a) and (b).
  4. None of these.
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Read the passage given below and answer the following questions:

A primary alkyl halide (A) C4H9Br reacted with akoholic KOH to give compound (B). Compound (B) is reacted with HBr to give compound (C) which is an isomer of (A). When (A) reacted with sodium metal, it gave a compound (D) C8H18 that is different than the compound obtained when n-butyl bromide reacted with sodium metal.

The following questions are multiple choice questions. Choose the most appropriate answer:

  1. Compound (A) is:

  1. CH3CH2CH2CH2Br

  2. $\text{CH}_3\text{CH}-\text{CH}_2\text{Br}\\\ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \text{CH}_3$

  3. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\text{CH}_3-\text{C}-\text{Br} \\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$

  4. CH3CH2CH2Br

  1. Which type of isomerism is present in compound (A) and (C)?
  1. Positional
  2. Functional
  3. Chain
  4. Both (a) and (c)
  1. Identify compound (B).
  1. $\text{CH}_3-\text{C}=\text{CH}_2 \ \ \\ \ \ \ \ \ \ \ \ \ \ \ \ \ \mid \\ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$
  2. CH3 – CH = CH – CH3
  3. CH3 – CH2 – CH = CH2
  4. None of these.
  1. IUPAC name of compound (D) is:
  1. N - octane
  2. 2, 5 - dimethylhexane
  3. 2 - methylheptane
  4. 3, 4 - dimethyl hexane.
  1. When compoound (C) is treated with ale. KOH and then treated with presence of peroxide, the compound obtained is:

  1. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\text{CH}_3-\text{C}-\text{Br} \\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$

  2. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\text{CH}_3-\text{CH}-\text{CH}_2-\text{Br}$

  3. $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Br}$

  4. $$$\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}-\text{Br}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ |\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{CH}_3$

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Read the passage given below and answer the following questions:

In haloalkanes, when a nucleophile stronger than the halide ion approaches the positively charged carbon atom of an alkyl halide, the halogen atom along with its bonding electron pair gets displaced and a new bond with the carbon and the nucleophile is formed. These reactions are called nucleophilic substitution reactions.

In these reactions the atom or group of atoms which loses its bond from carbon and takes on an additional pair of electrons is called leaving group. Halide ions are good leaving groups. Some important nucleophilic substitution reactions ofhaloalkanes with common nucleophiles are given in the table below.

 
Reagent
Nucleophile (Nu-)
Substitution product R-Nu
Class of main product
1.
NaOH or KOH or moist Ag2O
-OH
ROH
Alcohol
2.
H2O
H2O
ROH
Alcohol
3.
Nal
I-
R – I
Alkyl iodide
4.
R'NH2
$\text{R'}\ddot{\text{N}}\text{H}_2$
RNHR'
Sec. amine
5.
KCN
$\overline{\text{C}}\equiv\text{N}:$
RCN
Nitrile (cyanide)
6.
KNO2
O = N – O-
R – O – N = O
Alkvl nitrite

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: Alkyl halides are hydrolysed to alcohols by moist silver oxide.

Reason: RCI is hydrolysed to ROH easily but reactions slow down on addition of KI.

  1. Assertion: Alkyl halides fonn alkenes when heated above 300ºC.

Reason: CH3CH21 reacts slowly with strong base as compared to CD3CH2I.

  1. Assertion: RBr reacts with AgNO2 to give nitroalkane.

Reason: Silver nitrite (AgNO2) is an ionic compound, therefore the negative charge on nitrogen is the attacking site.

  1. Assertion: The nucleophilic substitution of vinyl chloride is difficult than ethyl chloride.

Reason: Vinyl group is electron donating group.

  1. Assertion: 2-Bromobutane on reaction with sodium ethoxide in ethanol gives 1-butene as the major product.

Reason: 1-Butene is less stable than 2-butene.

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Read the passage given below and answer the following questions:

An ideal solution may be defined as the solution which obeys Raoult's law exactly over the entire range of concentration. The solutions for which vapour pressure is either higher or lower than that predicted by Raoult's law are called non-ideal solutions.Non-ideal solutions can show either positive or negative deviations from Raoult's law depending on whether the A-B interactions in solution are stronger or weaker than A - A and B - B interactions.

The following questions are multiple choice questions. Choose the most appropriate answer:

  1. Which of the following solutions is/are ideal solution(s)?
  1. Bromoethane and iodoethane.
  2. Acetone and chloroform
  3. Benzene and acetone
  4. n-heptane and n-hexane
  1. Only I
  2. I and II
  3. II and III
  4. I and Iv
  1. For which of the following solutions $\Delta\text{H}_{\text{mix}}$ and $\Delta\text{V}_{\text{mix}}$ is negative?
  1. Acetone and aniline
  2. Ethyl alcohol and cyclohexane
  3. Acetone and CS2
  4. Benzene and toluene
  1. Which of the following is not true for positive deviations?
  1. The A-B interactions in solution are weaker than the A - A and B - B interactions.
  2. $\text{P}_\text{A}<\text{P}\mathring{\text{A}}\ \text{x}_\text{A}$ and $\text{P}_\text{B}<\text{P}\mathring{\text{B}}\ \text{x}_\text{B}$
  3. Carbon tetrachloride and chloroform mixture is an example of positive deviations.
  4. All of these.
  1. For water and nitric acid mixture, which of the given graph is correct?

 

  1.  

 

  1.  

  1. Both of these
  2. None of these
  1. Water-HCI mixture.
  1. Shows positive deviations.
  2. Forms minimum boiling azeotrope.
  3. Shows negative deviations.
  4. Forms maximum boiling azeotrope.
  1. I and II
  2. I and III
  3. I and IV
  4. III and IV
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Read the passage given below and answer the following questions:
Valence bond theory considers the bonding between the metal ion and the ligands as purely covalent. On the other hand, crystal field theory considers the metal-ligand bond to be ionic arising from electrostatic interaction between the metal ion and the ligands. In coordination compounds, the interaction between the ligand and the metal ion causes the five d-orbitals to split-up. This is called crystal field splitting and the energy difference between the two sets of energy level is called crystal field splitting energy. The crystal field splitting energy $(\Delta_0)$ depends upon the nature of the ligand. The actual configuration of complexes is divided by the relative values of $\Delta_0$ and P (pairing energy).
If $\Delta_0<\text{P},$ then complex will be high spin.
If $\Delta_0>\text{P},$ then complex will be low spin
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Which of the following ligand has lowest $\Delta_0$ value?
  1. CN-
  2. CO
  3. F-
  4. NH3
  1. The crystal field splitting energy for octahedral $(\Delta_0)$ and tetrahedral $(\Delta_t)$ complex is related as:
  1. $\Delta_\text{t}=\frac{1}{2}\Delta_0$
  2. $\Delta_\text{t}=\frac{4}{9}\Delta_0$
  3. $\Delta_\text{t}=\frac{3}{5}\Delta_0$
  4. $\Delta_\text{t}=\frac{2}{5}\Delta_0$
  1. On the basis of crystal field theory, the electronic configuration of d4 in two situations : (i) t.0 > P and (ii) t.0
  (i) (ii)
(a) $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$ $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$
(b) $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$ $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$
(c) $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$ $\text{t}^3_{2\text{g}}\text{e}^1_\text{g}$
(d) $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$ $\text{t}^4_{2\text{g}}\text{e}^0_\text{g}$
  1. Using crystal field theory, calculate magnetic moment of central metal ion of [FeF6]4-.
  1. 1.79B.M.
  2. 2.83B.M.
  3. 3.85B.M.
  4. 4.9B.M.
  1. Electronic configuration of d-orbitals in [Ti(H2O)6]3+ ion in an octahedral crystal field is:
  1. $\text{t}^1_{2\text{g}}\text{e}^0_\text{g}$
  2. $\text{t}^2_{2\text{g}}\text{e}^0_\text{g}$
  3. $\text{t}^0_{2\text{g}}\text{e}^1_\text{g}$
  4. $\text{t}^1_{2\text{g}}\text{e}^1_\text{g}$
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A reaction in which rate ofreaction is independent of concentration of the reactants is called zero order reaction. Photochemical combination of hydrogen and chlorine to give hydrogen chloride is an example of zero order reaction. The rate constant of a zero order reaction is equal to the rate of reaction. The half life period of a zero order reaction is directly proportional to initial concentration of the reactant. For a zero order reaction,

$\text{k}=\frac{1}{\text{t}}\left\{[\text{A}]-[\text{A}]\right\}$

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: For a zero order reaction, plot of rate vs concentration will be a straight line parallel to concentration axis.

Reason: For a zero order reaction, rate is independent of concentration.

  1. Assertion: Photochemical combination of hydrogen and chlorine to give hydrogen chloride is an example of zero order reaction.

Reason: The rate of reaction depends on the concentration of hydrogen and independent of concentration of chlorine.

  1. Assertion: If in a zero order reaction, the concentration of the reactant is doubled, the half-life period is also doubled.

Reason: For a zero order reaction, the rate of reaction is independent of initial concentration.

  1. Assertion: ln a reaction A → products, the concentration of the reactant is reduced to zero after a finite time.

Reason: The order of reaction is zero.

  1. Assertion: Rate constant of a zero order reaction has same units as the rate of reaction.

Reason: Rate constant of a zero order reaction does not depend on the unit of concentration.

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