Question Set B

CBSE 12th Chemistry Solutions Important Questions And Answers Study Material - QB365

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Questions:

Generic 2

7 x 2 = 14

How much charge is required for the reduction of 1 mole of Al³⁺ to AI?

What happpens when :
(i) CH₃ -CI is treated with aqueous KOH?
(ii) CH₃ -CI is treated with KCN?
(iii) CH₃ -Br is treated with Mg in the presence of dry ether ?

Define Raoult's law for binary solutions.

Write the structural formulae of compounds A, B and C and name the reagent D in the following reaction

How are the following conversions carried out?
(i) Phenol to Toluene
(ii) Ethanol to 1,1-dichloroethane.

Explain the following observations:
(i) Transition elements generally form colored compounds.
(ii) Zinc is not regarded as a transition element.

A first order decomposition reaction takes 40 minutes for 30% decomposition. Calculates its t_1/2 value.

Generic 5

3 x 5 = 15

(i) Define:
(a) Metal carbonyls
(b) Chelate
(ii) (a) Give one chemical test as an evidence to show that [Co(NH₃)₅CI]SO₄ and [Co(NH₃)₅(SO₄)] Cl are ionisation isomers.
(b) [NiCl₄]^2- is paramagnetic while [Ni(CO₄] is diamagnetic though both are tetrahedral. Why? (Atomic no. of Ni = 28)
(c) Write the electronic configuration of Fe(III) on the basis of crystal field theory when it forms an octahedral complex in the presence of (i) strong field ligand, and (ii) weak field ligand. (Atomic no. of Fe = 26)

Write the IUPAC names of the following coordination compounds
(i) [Co(NH₃)₆]Cl₃
(ii) [Co(NH₃)5Cl]Cl₂
(iii) K₃[Fe(CN)₆]
(iv) K₃[Fe(C2O₄)₃] (v) K₂[PdCl₄]
(v) [Pt(NH₃)2Cl(NH₂CH₃)]Cl

10.

(a) Describe the following giving linked chemical equations:
(i) Cannizzaro reaction
(ii) Decarboxylation
(b) Complete the following chemical equations:

(iii) \(C_6H_5CONH_2 \xrightarrow [heat] {H_3O^+}\)

Multiple Choice Question

12 x 1 = 12

11.

Predict the correct intermediate and the product in the following reaction:

(a)

(b)

(c)

(d)

12.

The stability of Mn²⁺, Fe²⁺,Cr²⁺, Co²⁺ is in order of (At o. of Mn = 25, Fe = 26, Cr = 24, Co = 27)

(a)

Mn²⁺ > Fe²⁺ > Cr²⁺ > CO²⁺

(b)

Fe²⁺ > Mn²⁺ > Co²⁺ > Cr²⁺

(c)

Co²⁺ > Mn²⁺ > Fe²⁺ > Cr²⁺

(d)

Cr²⁺ > Mn²⁺ > Co²⁺ > Fe²⁺

13.

The reagent(s) used for the reduction of aldehydes and ketone into alcohols is/are

(a)

fmely divided metals such as Pt/Pd/Ni

(b)

sodium borohydride

(c)

lithium aluminium hydride

(d)

All of the above

14.

Heterolyptic complex is

(a)

[Fe(CN)₆]^4-

(b)

[Co(NH₃)₅SO₄]⁺

(c)

[HgI₄]^2-

(d)

[CO(NH₃)₆]³⁺

15.

Which of the following hormones is produced under the conditions of stress which stimulate glycogenolysis in the liver of human beings?

(a)

Thyroxin

(b)

Insulin

(c)

Adrenaine

(d)

Estradiol

16.

In context of the lanthanoids, which of the following statements is not correct ?

(a)

All the members exhibit +3 oxidation state

(b)

Because of similar properties, the separation of lanthanoids is not easy.

(c)

Availability of 4f electrons results in the formation of compounds in +4 state for all the members of series.

(d)

There is a gradual decrease in the radii of the members with increasing atomic number in the series.

17.

In the following reaction, X is \(X\overset { Bromination }{ \longrightarrow } Y\overset { NaNO_{ 2 }\quad /HCI }{ \longrightarrow } Z\overset { Boiling }{ \underset { { C }_{ 2 }{ H }_{ 5 }OH }{ \longrightarrow } } Tribromobenzene\)

(a)

Benzoic acid

(b)

Salicylic acid

(c)

Phenol

(d)

Aniline

18.

Which of the following compound/s on halo-generation give a racemic mixture of products ?

(a)

(CH₃)₄C

(b)

CH₃CH₂CH₂CH₃

(c)

CH₃CH₂CH₃

(d)

CH₃CH₃

19.

Which of the following statements is not correct ?

(a)

Copper liberates hydrogen from acids

(b)

In its higher oxidation states, manganese forms stable compounds with oxygen and fluorine

(c)

Mn³⁺ and Co³⁺ are oxidising agents in aqueous solution

(d)

Ti²⁺ and Cr²⁺ are reducing agents in aqueous solution

20.

Which metal has highest density ?

(a)

(b)

(c)

(d)

21.

75% of the first order reaction was completed in 32 min. 50% of the reaction was completed in

(a)

24 min

(b)

8 min

(c)

16 min

(d)

4 min

22.

The van't Hoff factor i for a compound which undergoes dissociation in one solvent and association in other solvent is respectively

(a)

Greater than one and greater than one

(b)

Less than one and greter than one

(c)

Less than one and less than one

(d)

Greater than one and less than one

Generic 3

6 x 3 = 18

23.

Convert:
(i) Benzoic acid to Benzaldehyde
(ii) Acetylene to Ethanal
(iii) Acetic acid to Methane

24.

What happens when:
(i) Ethanol is treated with Cu at 573 K.
(ii) Phenol is treated with CH₃COCl / anhydrous AlCl₃.
(iii) Ethyl chloride is treated with NaOCH₃?

25.

Write the IUPAC name of the following compounds:

26.

Explain the following observations:
(i) With the same d-orbital configuration (d⁴), Cr²⁺ ion is a reducing agent while Mn³⁺ ion is an oxidising agent.
(ii) Cu⁺ ion is not stable in aqueous solutions.
(iii) Among the 3d series of transition elements, the largest number of oxidation states are exhibited by manganese.

27.

Give the structure of A, B and C in the following reactions:
(i) \({ C }{ H }_{ 3 }Br\overset { KCN }{ \longrightarrow } A\overset { LiAIH_{ 4 } }{ \longrightarrow } B\overset { { HNO }_{ 2 } }{ \underset { 273K }{ \longrightarrow } } C\)
(ii) \({ C }{ H }_{ 3 }COOH\overset { { NH }_{ 3 } }{ \underset { \triangle }{ \longrightarrow } } A\overset { Br_{ 2 }+KOH }{ \longrightarrow } B\overset { { CHCI }_{ 3 }+NaOH }{ \longrightarrow } C\)

28.

Write the types of isomerism exhibited by the following complexes:
(i) \(\left[ Co{ \left( { NH }_{ 3 } \right) }_{ 5 }Cl \right] { SO }_{ 4 }\)
(ii) \({ \left[ Co{ \left( en \right) }_{ 3 } \right] }^{ 3+ }\)
(iii) \(\left[ Co{ \left( { NH }_{ 3 } \right) }_{ 6 } \right] \left[ Cr{ \left( CN \right) }_{ 6 } \right] \\ \)

Assertion and reason

3 x 1 = 3

29.

Assertion : Molarity of a solution in liquid state changes with temperature.
Reason : The volume of a solution changes with change in temperature.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

30.

Assertion: Aldol condensation can be catalysed both by acids and bases.
Reason: \(\beta\)-Hydroxy aldehydes or ketones readily undergo acid catalysed dehydration.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

31.

Assertion: Fe²⁺ is paramagnetic.
Reason: Fe²⁺ contains four unpaired electrons
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement

Case Study Questions

2 x 4 = 8

32.

When the mixture contains the three amine salts (1°,2° and 3°) along with quaternary salt, it is distilled with KOH solution. The three amines distill, leaving the quaternary salt unchanged in the solution. Then the mixture of amines is separated by fractional distillation, Hinsbergs method, and Hoffmann’s method.

(i) Hinsberg reagent is
(a) aliphatic sulphonyl chloride
(b) phthalamide
(c) aromatic sulphonyl chloride
(d) anhydrous ZnCl₂ + conc. HCl.
(ii) Primary amine with Hinsberg’s reagent forms
(a) N-alkyl benzene sulphonamide soluble in KOH solution
(b) N-alkyl benzene sulphonamide insoluble in KOH solution
(c) N,N-dialkyl benzene sulphonamide soluble in KOH solution
(d) N,N-dialkyl benzene sulphonamide insoluble in KOH solution.
(iii) To separate amines in a mixture Hoffmann’s method is used. The Hoffmann’s reagent is
(a) benzenesulphonyl chloride
(b) diethyloxalate
(c) benzeneisocyanide
(d) p-toulenesulphonic acid.
(iv) 3⁰ amines with Hinsberg’s reagent give
(a) no reaction
(b) product which is same as that of 1⁰ amine
(c) product which is same as that of 2° amine
(d) products which is a quaternary salt.

33.

Read the passage given below and answer the following questions :
Carboxylic acids dissociate in water to give carboxylate ion and hydronium ion.
RCOOH + H₂O \(\longrightarrow\) RCOO^- + H3O⁺
The acidity of carboxyl group is due to the presence of positive charge on oxygen which liberates proton. The carboxylate ion formed is resonance stabilised.

Carboxylic acids are stronger acids than phenols. Electron withdrawing groups (EWG) increase the acidity of carboxylic acids by stabilising the conjugate base through delocalisation of negative charge by inductive and/ or resonance effects. Electron donating group (EDG) decrease the acidity by destabilising the conjugate base.
The following questions are multiple choice questions. Choose the most appropriate answer :
(i) Which of the following reactions is showing the acidic property of carboxylic acid?

(ii) Which one of the following is the correct order of acidic strength?

(a) CF₃COOH > CHCl₂COOH > HCOOH > C₆H₅CH₂COOH > CH₃COOH

(b) CH₃COOH > HCOOH > CF₃COOH > CHCl₂COOH > C₆H₅CH₂COOH

(c) HCOOH > C₆H₅CH₂COOH > CF₃COOH > CHCl₂COOH > CH₃COOH

(d) CF₃COOH > CH₃COOH > HCOOH > CHCl₂COOH > C₆H₅CH₂COOH

(iii) Which of the following acids has the smallest dissociation constant?

(a) CH₃CHFCOOH	(b) FCH₂CH₂COOH
(c) BrCH₂CH₂COOH	(d) CH₃CHBrCOOH

(iv) The correct order of acidity for the following compounds is

(a) I > II > III > IV	(b) III > I > II > IV
(c) III> IV > II> I	(d) I > III > IV > II

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Answers Key:

Generic 2

7 x 2 = 14

The number of electrons involved in the reaction is three.
Therefore, the amount of electricity required for one mole
of AI³⁺ ions = 3F or 3 x 96500C = 289500C

(i) CH₃ - CI + KOH\(\rightarrow\)CH₃OH + KCI
(aq) Methanol
(ii) CH₃ - CI + KCM \(\rightarrow\) CH₃ CN + KCI
Methyl cyanide
(iii) CH₃ Br + Mg \(\overset { Dry\ ether }{ \longrightarrow } \)CH₃MgBr
Methyl magnesium bromide

Define Raoult's law for binary solutions may be defined as: at a given temperature, for a solution of two volatile liquids the partial vapour pressure of each component of the solution is equal to the product of the vapour pressure of the pure component and its mole fraction in solution. Thus,
\(P_A=P_A \quad{ }^{\circ} \times x_a \text { and } P_B=P_B \quad{ }^{\circ} \times x_B\)

(i) It is due to presence of unpaired electrons in d-orbitals therefore, they undergo d-d transitions by absorbing light from visible region and rediate complementary colour.
(ii) It is because neither Zn nor Zn²⁺ ion has incompletely filled d-orbital.

\(k=\frac { 2.303 }{ { t }_{ { 1 }/{ 2 } } } \log { \frac { { [R] }_{ 0 } }{ { { [R] } } } }\)
\(k=\frac { 2.303 }{ 40 } \log { \frac { { [R] }_{ 0 } }{ { \frac { 70 }{ 100 } { [R] }_{ 0 } } } } \)
[30% is decomposed, 70% is left]
\(k=\frac { 2.303 }{ 40 } \left( \log { 10 } -\log { 7 } \right) \)
\(k=\frac { 2.303 }{ 40 } [1.0000-0.8451]\)
\(k=\frac { 2.303 }{ 40 } \times 0.1549\)
\(k=\frac { 0.3567 }{ 40 } =8.917\times { 10 }^{ -3 }{ min }^{ -1 }\)
\({ t }_{ { 1 }/{ 2 } }=\frac { 0.693 }{ k } =\frac { 0.693 }{ 8.917\times { 10 }^{ -3 } } \)
\(=\frac { 0.693 }{ 8.917 } =77.716 \ min\)

Generic 5

3 x 5 = 15

(i) (a) Metal carbonyls: Metal carbonyls are the compounds in which carbon monoxide (CO) acts as the ligand. The metal-carbon bond in metal carbonyls possesses both \(\sigma\) and \(\pi\) characters, e.g. N(CO)₄[nickeltetracarbonyl]. Its IUPAC name is tetra carbonyl nickel(0).
(b) Chelate: An inorganic metal complex in which there is a close ring of atoms caused by attachment of a ligand to a metal atom at two points. An example is the complex ion formed between ethylene diamine and cupric ion,[Cu(NH₂CH₂CH₂NH₂)₂]²⁺.

(ii) (a) Add BaCl₂ solution. [Co(NH₃)]₅Cl]SO₄ will give white ppt. of BaSO₄.
\(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{SO}_{4}+\mathrm{BaCl}_{2}(a q) \)\( \longrightarrow\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl}_{2}+\mathrm{BaSO}_{4} \downarrow \)
  \(\text { (White ppt.) }\)
Add AgNO₃(aq) solution [Co(NH₃)₅SO₄] Cl will give white ppt. of AgCl.
\( {\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right] \mathrm{Cl}+\mathrm{AgNO}_{3}(a q)} \) \(\longrightarrow \mathrm{AgCl}+\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right] \mathrm{NO}_{3} \)
  \(\text { (White ppt) }\)
(c) Fe³⁺ (4s⁰3d⁵) In strong field \( \Delta_{0}>P t_{2 g}^{5} e g^{0} \)
In weak field \(\Delta_{0}

(i) Pentaamminechloridocobalt(III) chloride.
(ii) Pentaamminechloridocobalt(III) chloride.
(iii) Potassium hexacyanoferrate(III).
(iv) Potassium tetrachloridopalladate(II).
(v) Diamminechlorido(methylamine)platinum(II) chloride.

10.

(a) (i) Cannizzaro's reaction:
When aldehydes which do not have \(\alpha\)-hydrogen gets oxidised as well as reduced in presence of conc. alkali, it is called Cannizzaro's reaction.
\(\underset { Methanal }{ 2HCHO } \overset { 50%NaOH }{ \longrightarrow } \underset { Sodium\quad Methanoate }{ HCOONa } +\underset { Methanol }{ CH_{ 3 }OH } \)
(ii) Decarboxylation : Sodium salts of acids when heated with soda lime, lower alkanes are formed
\(\underset { Sodium\quad acetate }{ CH_{ 3 }COONa } +\underset { Sodalime }{ NaOH } \longrightarrow \underset { Methane }{ CH_{ 4 } } +\underset { sodium\quad carbonate }{ Na_{ 2 }CO_{ 3 } } \)

Multiple Choice Question

12 x 1 = 12

11.

12.

(a)
Mn²⁺ > Fe²⁺ > Cr²⁺ > CO²⁺

13.

(d)
All of the above

14.

(b)
[Co(NH₃)₅SO₄]⁺

15.

16.

17.

(d)
Aniline

18.

(b)
CH₃CH₂CH₂CH₃

19.

(a)
Copper liberates hydrogen from acids

20.

(b)
Os

21.

22.

In case of dissociation, i>1 and in case of association, i>1.

Generic 3

6 x 3 = 18

23.

24.

25.

26.

(iii) Manganese exhibits all the oxidation states from + 2 to + 7. It shows largest number of oxidation states as it has the maximum number of unpaired electrons.

27.

(i) \({ C }{ H }_{ 3 }Br\overset { KCN }{ \longrightarrow } { C }{ H }_{ 3 }CN\overset { LiAIH_{ 4 } }{ \longrightarrow } { C }{ H }_{ 3 }{ C }{ H }_{ 2 }{ NH }_{ 2 }\overset { { HNO }_{ 2 } }{ \underset { 273K }{ \longrightarrow } } { C }{ H }_{ 3 }{ C }{ H }_{ 2 }-OH\)
(ii) \({ C }{ H }_{ 3 }COOH\overset { { NH }_{ 3 } }{ \underset { \triangle }{ \longrightarrow } } { C }{ H }_{ 3 }{ C }{ ONH }_{ 2 }\overset { Br_{ 2 }+KOH }{ \longrightarrow } { C }{ H }_{ 3 }{ NH }_{ 2 }\overset { { CHCI }_{ 3 }+NaOH }{ \longrightarrow } { C }{ H }_{ 3 }NC\)

28.

(i) ionisation isomerism
(ii) optical isomerism
(iii) coordination isomerism

Assertion and reason

3 x 1 = 3

29.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

30.

(b): Both carbanions (formed in presence of base) and enol form (formed in presence of an acid) act as nucleophiles and hence add on the carbonyl group of aldehydes and ketones to give aldols.

31.

(a): Fe has atomic number 26. So, its electronic configuration is [Ar]3d⁶4s².
Fe²⁺has electronic configuration [Ar]3d⁶.

It has four unpaired electrons and it is paramagnetic.

Case Study Questions

2 x 4 = 8

32.

1.(c) aromatic sulphonyl chloride
2.(a) N-alkyl benzene sulphonamide soluble in KOH solution
3.(b) diethyloxalate
4.(a) no reaction

33.

(i) (d): All the reactions are showing the acidic properties of carboxylic acid. Carboxylic acid forms the sodium salts with all i.e., alkali metals, NaOH and Na₂CO₃ etc. and removes the acidic proton from the carboxylic acid.
(ii) (a): In general, greater the +I effect of the group attached to the carboxyl group, lesser will be the acidic strength and greater the -I effect ofthe group, greater will be acidic strength. As number of halogen atoms and electronegativity of halogen atom increases, acidic strength increases. Thus, correct order of acidic strength is
CF₃COOH> CHCl₂COOH > HCOOH > C₆H₅CH₂COOH > CH₃COOH
(iii) (c) : Stronger -I group attached closer to - COOH makes the acid stronger, i.e., acid has the larger dissociation constant. - Br shows poor (-I) effect and also far away from -COOH group i.e., option (c) has smallest dissociation constant.
(iv) (a): Due to ortho-effect, (I) and (II) are stronger acids than (III) and (IV). Due to two ortho-hydroxyl groups in (I), it is stronger acid than (II). (III) is a stronger acid than (IV) because at m-position, -OH group cannot exert its +R effect but can only exert its -I effect while at p-position, -OH group exerts its strong +R effect. Thus, the correct order of acidity is : I > II > III > IV.