Question Set C

CBSE 12th Standard Chemistry Aldehydes , Ketones and Carboxylic Acids HOT Questions Study Material - QB365

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Questions:

Generic 2

5 x 2 = 10

Describe the following.
(i) Cannizzaro reaction
(ii) Cross aldol condensation

A first order reaction takes 40 min for 30%. decomposition. Calculate t_1/2

What happens when D-glucose is treated with the following reagents ?
(i) HI
(ii) Bromine water
(iii) HNO₃.

Why a mercury cell gives a constant voltage throughout its life ?

Mention one commercial use of N, N-Dimethylaniline (DMA).

Generic 3

7 x 3 = 21

Write the major product(s) in the following reactions.

The standard electrode potential for Daniell cell is 1.1V. Calculate the standard Gibbs energy for the reaction:
Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Predict the products of the following reactions:
(i)

(ii)

(iii)

(iv)

Elimination of H₂O from carbonyl and amine group and formation of C= N bond.

The rate of most reactions becomes double when their temperature is raised from 298 K to 308 K. Calculate their activation energy.

10.

A galvanic cell consits of a metalic zinc plate immersed in 0.1 M Zn(NO₃)₂ solution and metalic plate of lead in 0.02 M Pb(NO₃)₂solution. Calculate the emf of the cell Write the chemical equation for the electrode reactions and represent the cell. (Given E⁰ _{Zn²⁺, Zn} = -0.76V,E⁰ _{Pb²⁺, Pb} = -0.13 V)

11.

Why is carboxyl group in benzoic acid meta directing? Support your answer with two examples.

12.

Answer the following questions briefly:
(i) What are any two good sources of Vitamin A?
(ii) What are nucleotides?

Multiple Choice Question

16 x 1 = 16

13.

The \(\alpha\)- and \(\beta\)-glucose are

(a)

isomers of D( +) glucose and L( -) glucose respectively.

(b)

diastereomers of glucose

(c)

anomers of glucose

(d)

isomers which differ in the configuration of C-2.

14.

A is

(a)

(b)

(c)

(d)

15.

Mechanism of a hypothetical reaction X₂+ Y₂ \(\rightarrow\)2 x Y is given below
\(\mathrm{a}_{2} \rightleftharpoons x+x(\text { fast })\)
X + Y₂ \(\rightarrow\) XY + Y (slow)
X + Y\(\rightarrow\) XY (fast)
The overall order of reaction is

(a)

(b)

(c)

1.5

(d)

16.

Which of the following polysaccharide is stored in the cell wall in plant cells?

(a)

Cellulose

(b)

Amylose

(c)

Amylopectin

(d)

Glycogen

17.

The correct name for yellow dye is

(a)

p-hydroxy azobenzene

(b)

p-amino azobenzene

(c)

o-hydroxyazobenzene

(d)

o-amino azobenzene

18.

The reaction, \(\begin{equation} \mathrm{ArN}_{2}^{+} \mathrm{Cl}^{-} \stackrel{\mathrm{Cu} / \mathrm{HCl}}{\longrightarrow} \mathrm{ArCl}+\mathrm{N}_{2}+\mathrm{CuCl} \end{equation}\) is named as

(a)

Sandmeyer reaction

(b)

Gattermann reaction

(c)

Claisen reaction

(d)

Carbylamine reaction

19.

What would be the side products formed with primary amine in the Hofmann bromamide degradation reaction?

(a)

Na₂CO₃ + NaBr

(b)

NaBr + H₂O + NaOH

(c)

NaBr + H₂O + Na₂CO₃

(d)

Br₂ + H₂O + Na₂CO₃

20.

In the given reaction,
2Cu⁺(aq) \(\rightleftharpoons\) Cu²⁺(aq) + Cu(s)
E^O_Cu+_/Cu = 0.6 V and E^oCu²⁺/Cu = 0.41 V
Find out the equilibrium constant.

(a)

2.76 x 10²

(b)

2.76 X 10⁴

(c)

2.76 X 10⁶

(d)

2.76 x 10⁸

21.

Which functional group participates in disulphide bond formation in proteins ?

(a)

Thioether

(b)

Thiol

(c)

Thioester

(d)

Thiolactone

22.

Aldol condensation does not occur between

(a)

two different aldehydes

(b)

two different ketones

(c)

an aldehyde and a ketone

(d)

an aldehyde and an ester

23.

Hydrolysis products of lactose are

(a)

glucose and glucose

(b)

glucose and fructose

(c)

glucose and galactose

(d)

none of these

24.

The IUPAC name of the compound is

(a)

4-methoxy-2-nitrobenzaldehyde

(b)

4-formyl-3-nitroanisole

(c)

4-methoxy-6-nitrobenzaldehyde

(d)

2-formy-5-methoxynitrobenzene

25.

E₁ , E₂ and E₃ are the emf values of the three galvanic cells respectively
(i) Zn | Zn²⁺ (1 M) || Cu²⁺(0.1 M) | Cu
(ii) Zn | Zn²⁺ (1 M) || Cu²⁺(1 M) | Cu
(iii) Zn | Zn²⁺ (0.1 M) || Cu²⁺(1 M) | Cu
Which one of the following is true ?

(a)

E₂ > E₃ > E₁

(b)

E₃ > E₂ > E₁

(c)

E₁> E₂ > E₃

(d)

E₁> E₃ > E₂

26.

The rate constant of a second order reaction, 2A\(\longrightarrow\) Products, is 10^-4 lit mol^-1 min^-1. The initial concentration of the reactant is 10^-2mol lit^-1. What is the half-life (in min) ?

(a)

(b)

1000

(c)

100

(d)

10⁶

27.

Which of the following statements are in accordance with the Arhenius equation ?

(a)

Rate of a reaction increases with decrease in temperature

(b)

Rate of a reaction increases with decrease in activation energy

(c)

Rate constant decreases exponentially with increase in temperature

(d)

Rate of reaction decreases with decrease in activation energy

28.

In the electrolysis of aqueous sodium chloride solution which of the half cell reaction will occur at anode?

(a)

\({ Na }^{ + }(aq)+{ e }^{ - }\longrightarrow Na(s);{ E }_{ cell }^{ \circleddash }=-2.71V\)

(b)

\(2{ H }_{ 2 }O(l)\longrightarrow { O }_{ 2 }(g)+4{ H }^{ + }(aq)+4{ e }^{ - };{ E }_{ cell }^{ \circleddash }=1.23V\)

(c)

\({ H }^{ + }(aq)+{ e }^{ - }\longrightarrow \frac { 1 }{ 2 } { H }_{ 2 }(g);{ E }_{ cell }^{ \circleddash }=0.00V\)

(d)

\({ Cl }^{ - }(aq)\longrightarrow \frac { 1 }{ 2 } { Cl }_{ 2 }(g)+{ e }^{ - };{ E }_{ cell }^{ \circleddash }=1.36V\)

Generic 5

3 x 5 = 15

29.

(a) How will you convert the following:
(i) Propanone to Propan-2-ol
(ii) Ethanal to 2-Hydroxypropanoic acid
(iii) Toluene to Benzoic acid
(b) Give simple chemical test to distinguish between:
(i) Pentan-2-one and Pentan-3-one
(ii) Ethanal and Propanal

30.

Write the cell reaction and calculate the emf of the following cell at 298 K.
Sn(s) I Sn²⁺(0.004 M) II H⁺(0.020 M) I H₂(g) (1 bar) I Pt(s) (Give: E^O_{Sn2+ /Sn} = - 0.14 V)
(b) Give reasons: (i) On the basis of E^O values, O₂ gas should be liberated at anode, but it is Cl₂ gas which is liberated in the electrolysis of aqueous NaCl
(ii) Conductivity of CH₃COOH decreases on dilution.

31.

(a) Write the structures of the main products when aniline reacts with the following reagents:
(i) Br₂ water
(ii) HCI
(iii) (CH₃CO)₂O / pyridine
(b) Arrange the following in the increasing order of their boiling point:
C₂H₅NH₂ , C₂H₅OH, (CH₃)₃N
(c) Give a simple chemical test to distinguish between the following pair of compounds:
(CH₃)₂NH and (CH₃)₃N

Passage Based Questions

4 x 1 = 4

32.

Glucose is an aldohexose. It can occur freely as well as in combined form in the nature. It is present in sweet fruits and honey. It is also present in quantities in ripe grapes. As glucose is an aldohexose, it consists of six C-atoms and an aldehyde group. It is the most abundant organic compound on the earth and used as an immediate source of energy for all metabolic reactions in the animals.
It was found that glucose forms a six membered ring in which -OH at C-5 is involved in the ring formation. The cyclic six membered structure of glucose is known as pyranose structure. It is analogous to pyran which is a cyclic organic compound with one oxygen atom and five carbon atoms in the ring.
Write the reaction for the preparation of glucose from sucrose.

33.

Basic character of amines depend upon the ease for the formation of cation by accepting a proton from the acid. The more stable the cation is relative to the amine, more basic is the amine. Basicity of an amine in aqueous solution depends upon stability of ammonium cation formed by accepting proton from water. The stability of ammonium cation depends upon the following three factors:
(i) + I-effect (alkyl group)
(ii) Sterk effect (alkyl group)
(iii) Solvation effect
(CH₃)₂NH is more basic than (CH₃)₃N in an aqueous solution. Why?

34.

Carboxylic acids evolve hydrogen with metals and form salts with alkalies similar to phenols. However, unlike phenols, they react with weaker bases like sodium carbonate and hydrogen carbonate to evolve carbon dioxide. In aqueous solution, carboxylic acids ionise and exist in dynamic equilibrium between the resonance stabilised carboxylate ions and the hydronium ions.

Resonance stabilisation of carboxylate anion is more than that of undissociated carboxylic acid. Therefore, greater stability of carboxylate ion is responsible for the acidic character of carboxylic acids. Carboxylic acids are more acidic than alcohols because carboxylate anions are more stable than alkoxide ions, so carboxylic acids have strong tendency to release a proton.
Arrange benzoic acid, 3, 4-dinitrobenzoic acid, 4-methoxybenzoic acid in increasing order of acidic strength.

35.

Molar conductivity of a solution is the conductance of solution containing one mole of electrolyte, kept between two electrodes having unit length between them and large cross sectional area so as to contain the electrolyte. In other words, molar conductivity is the conductance of the electrolytic solution kept between the electrodes of a conductivity cell at unit distance but having area of cross section large enough to accommodate sufficient volume of solution that contains one mole of the electrolyte. It is denoted by Λ_m.
Write the mathematical expression for molar conductivity.

Case Study Questions

1 x 4 = 4

36.

Read the passage given below and answer the following questions:
Carboxylic acids having an a-hydrogen atom when treated with chlorine or bromine in the presence of small amount of red phosphorus gives a-halo carboxylic acids. The reaction is known as Hell- Volhard-Zelinsky reaction.

When sodium salt of carboxylic acid is heated with soda lime it loses carbon dioxide and gives hydrocarbon with less number of C-atoms.

In these questions (i - iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(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.
(i) Assertion: (CH₃)₃CCOOH does not give H.V.Z reaction.
Reason: (CH₃)₃CCOOH does not have \(\alpha\)-hydrogen atom.
(ii) Assertion: H.V.Z. reaction involves the treatment of carboxylic acids having \(\alpha\)-hydrogens with Cl₂ or Br₂in presence of small amount of redphosphorus.
Reason : Phosphorus reacts with halogens to form phosphorus trihalides.
(iii) Assertion: C₆H₅COCH₂COOH undergoes decarboxylation easily than C₆H₅COCOOH.
Reason : C₆H₅COCH₂COOH is a 13-ketoacid.
(iv) Assertion: On heating 3-methylbutanoic acid with soda lime, isobutane is obtained.
Reason: Soda lime is a mixture of NaOH + CaO in the ratio 3 : 1.

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Answers Key:

Generic 2

5 x 2 = 10

(i) Cannizzaro reaction Aldehydes (not having alpha hydrogen atoms) undergo self oxidation-reduction (disproportionation) reaction. One molecule is oxidized to carboxylic acid and another molecule is reduced to alcohol. Concentrated alkali is the reagent.
(iii) Cross aldol condensation between different carbonyl compounds (aldehydes and ketones). If both reactants contain alpha hydrogen atoms, four different products can be obtained.

Let \( a=100, a-x=100-30=70, t=40 \mathrm{~min} \)
\(k=\frac{2.303}{t} \log \frac{a}{(a-x)}=\frac{2.303}{40 \mathrm{~min}} \log \frac{100}{70}\)
\(=\frac{2.303}{40} \log \frac{10}{7}=\frac{2.303}{40} \log 1.428=\frac{2.303}{40} \times 0.1545\)
\(k=8.91 \times 10^{-3} \min ^{-1} \)
\(t_{1 / 2}=\frac{0.693}{\mathrm{k}}=\frac{0.693}{8.91 \times 10^{-3} \min ^{-1}}=77.78 \mathrm{~min} \)
\(t_{1 / 2}=77.78 \mathrm{~min}\)

(i) When glucose is treated with HI, it forms n-hexane, suggesting that all the six carbon atoms are linked in a straight line.

(ii) On heating glucose with bromine water, it gets oxidised to six carbon carboxylic acid, gluconic acid.

(iii) Glucose on treatment with nitric acid gives a dicarboxylic acid, saccharic acid.

This is because the electrolyte KOH is not consumed in the reaction.

It is used in preparation of dyes.

Generic 3

7 x 3 = 21

\(\Delta_{\mathrm{r}} G^{\ominus}=-n F \mathrm{E}_{\text {(cell) }}^{\ominus}\)
n in the above equation is 2, F = 96487 C mol ^–1 and \(\mathrm{E}_{\text {(cell })}^{\ominus}\) = 1.1 V
Therefore, \(\Delta_{\mathrm{r}} G^{\ominus}\) = – 2 × 1.1V × 96487 C mol ^–1
= – 21227 J mol^–1
= – 212.27 kJ mol^–1

(i) Cyclopentanone reacts with hydroxyl amine to form oxime.

(ii) \(\text { a } \beta\)unsaturated aldehyde reacts with semicarbazide (H₂NCONHNH₂) to form semicarbazone.

(iii) Cyclohexanone reacts with 2,4-dinitro phenyl hydrazine to form 2,4-dinitro phenyl hydrazone.

(iv) Acetophenone reacts with ethyl amine to form an imine

T₁= 298 K, T₂= 308 k.
R = 8.314 J mol^-1 K^-1
Activation energy
k₂=2k₁
\(log\frac{k_2}{k_1}=\frac{E_a}{2.303R}[\frac{1}{T_1}-\frac{1}{T_2}]\)
\(\Rightarrow\ \ log2=\frac{E_a}{19.15 \ J\ mol^{-1}}[\frac{1}{298}-\frac{1}{308}]\)
\(E_a=\frac{0.3010\times19.15\times 298\times 308}{10}J\ mol^{-1}\)
\(E_a=52905 \ J\ mol^{-1}\ or \ 52.905\ kJ\ mol^{-1}\)

10.

0.6094 V, Zn + Pb²⁺ \(\longrightarrow\) Zn²⁺ + Pb; Zn|Zn²⁺ (0.1 M) || Pb²⁺ (0.02 M) Pb

11.

In benzoic acid, carboxyl group is meta-directing because it is electron withdrawing, therefore, there is +ve charge on 0- and p-positions, therefore, electrophilic substitution takes places at m-position due to greater electron density, e.g

12.

(i) Carrot and Cod liver oil.
(ii) Nucleotides are monomers of nucleic acids. They consist of heterocyclic base, pentose sugar and phosphoric acid residue.

Multiple Choice Question

16 x 1 = 16

13.

14.

15.

16.

(a)
Cellulose

17.

(b)
p-amino azobenzene

18.

(b)
Gattermann reaction

19.

20.

21.

(b)
Thiol

22.

(d)
an aldehyde and an ester

23.

24.

(a)
4-methoxy-2-nitrobenzaldehyde

25.

(b)
E₃ > E₂ > E₁

26.

(d)
10⁶

27.

(b)
Rate of a reaction increases with decrease in activation energy

28.

(b)
\(2{ H }_{ 2 }O(l)\longrightarrow { O }_{ 2 }(g)+4{ H }^{ + }(aq)+4{ e }^{ - };{ E }_{ cell }^{ \circleddash }=1.23V\)

Generic 5

3 x 5 = 15

29.

(b) (i) Add I₂ and NaOH. Pentan-2-one will give yellow ppt. due to iodoform, whereas pentan-3-one will not.
(ii) Add I₂ and NaOH. Ethanal will give yellow ppt. of iodoform, whereas propanal will not.

30.

\(\mathrm{Sn}(\mathrm{s}) \mid \mathrm{Sn}^{2+}(0.004 \mathrm{M}) \| \mathrm{H}^{+}(0.020 \mathrm{M}) \mid \mathrm{H}_{2}(g)(1 \text { bar }) \mid \operatorname{Pt}(s)\)
Cell reaction is
\(\mathrm{Sn}+2 \mathrm{H}^{+}(0.020 \mathrm{M}) \rightarrow \mathrm{Sn}^{2+}(0.004 \mathrm{M})+\mathrm{H}_{2}(1 \mathrm{bar})\)
\(E_{\mathrm{cell}}^{\circ}=E_{\mathrm{H}^{+}}^{\circ} \cdot \frac{1}{2} \mathrm{H}_{2}-E_{\mathrm{Sn}}^{2+} / \mathrm{Sn} \)
\(=0-(-0.14 \mathrm{~V})=0+0.14 \mathrm{~V}=0.14 \mathrm{~V}\)
for calculation of emf apply Nernst equation;
\(E_{\text {cell }} =E_{\text {cell }}^{\circ}-\frac{0.0591}{n} \log \frac{\left[\mathrm{Sn}^{2+}\right] \times p_{\mathrm{H}_{2}}}{\left[\mathrm{H}^{+}\right]^{2}} \)
\(=0.14-\frac{0.0591}{2} \log \frac{[0.004] \times 1}{[0.020]^{2}} \)
\(=0.14-\frac{0.0591}{2} \log \frac{0.004}{0.0004} \\ =0.14-\frac{0.0591}{2} \log 10 \\ =0.14-\frac{0.0591}{2}=0.110 \mathrm{~V}\)
(b) (i) From standard oxidising potential it is clear that oxygen gas should be liberated at anode, but its rate of production is very low. In order to increase that we increase the voltage of external battery Because of which chloride ions get oxidised easily and Cl₂ gas is liberated at anode.
(ii) Conductivity of solution is conductance of ions present in unit volume of solution. On dilution number of CH₃COOH ions per unit volume decreases. Hence conductivity decreases.

31.

(ii) Alcohols have higher boiling point as compared to that of amines, because oxygen being more electronegative atom, forms strong hydrogen bond as compared to that of nitrogen. In tertiary amine, there is no hydrogen bond formation due to the absence of H-atoms and hence, has the lowest boiling point. Therefore, increasing order of boiling point (CH₃)₃N < C₂H₅NH₂ < C₂H₅OH .
(iii) (CH₃)₃NH and (CH₃)₃N are secondary and tertiary arnines respectively. These are distinguished by Hinsberg's reagent which gives sulphonamide with secondary amines and no reaction carried out with tertiary arnines. (CH₃)₃NH reacts with benzene sulphonyl chloride as follows:

Passage Based Questions

4 x 1 = 4

32.

\(\begin{equation} \mathrm{C}_{12} \mathrm{H}_{12} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{O} \stackrel{\mathrm{H}^{+}}{\longrightarrow} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\\ Sucrose\quad\quad\quad\quad\quad Glucose \quad\quad Fructose \end{equation}\)

33.

In aqueous solution, basic nature depends on + I-effect, H-bonding and steric effect. The combined effectshows that (CH₃)₂ NH is more basic than (CH₃)₃N as H-bonding is more in case of (CH₃)₂ NH than in (CH₃)₃N which predominates over the stability due to + I effect of three - CH₃groups.

34.

4-methoxybenzoicacid < benzoic acid < 3, 4-dinitro benzoic acid.

35.

The mathematical expression for molar conductivity is given as,
\(\Lambda_{\mathrm{m}}=\frac{K \times 1000}{M}\\ where, \Lambda_{\mathrm{m}}= Molar \ conductivity \ of \ solution\)
K = Conductivity of solution
M = Molarity of the solution

Case Study Questions

1 x 4 = 4

36.

(i) (a)
(ii) (c): Phosphorus converts a little .of the acid into acid chloride which is more reactive than the parent carboxylic acid. Thus, it is the acid chloride, not the acid itself, that undergoes chlorination at the \(\alpha\)-carbon.
(iii) (a): \(\beta\)-ketoacids are unstable acids. They readily undergo decarboxylation through a cyclic transition state.

(i) (b): All aliphatic aldehydes give red ppt. with
Fehling's solution, but ketones do not reduce Fehling's
solution.
(ii) (e): Aliphatic aldehydes reduce Fehling's solution,
but aromatic aldehydes do not.