Question Set C

CBSE 12th Standard Chemistry d- and f- Block Elements HOT Questions Study Material - QB365

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Questions:

Generic 3

5 x 3 = 15

How would you account for the following?
(i) Metal-metal bonding is more extensive in the 4d and 5d -series of transition elements than 3d -series.
(ii) Mn (III) undergoes disproportionation reaction easily.
(iii) Co (II) is easily oxidised in the presence of strong ligands

In a particular reduction process,the concentration of solution that is initially 0.24M is reduced to 0.12M in 10 hours and 0.06M in 20 hours.What is the rate constant of this reaction?

Nitrogen dioxide (NO₂)reacts with fluorine(F₂)to form nitryl fuoride(NO₂F)
2NO₂(g)+F₂(g)\(\longrightarrow\)2NO₂F(g)
Write the rate of reaction in terms of
(i) rate of formation of NO₂F
(ii) rate of disappearance of NO₂
(iii) rate of disappearance of F₂

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of solute (associated or dissociated). (Given : Molar mass of benzoic acid = 122 g mol^-1 , K_f for benzene = 4.9 K kg mol^-1)

Explain the following:
(i) The transition elements have great tendency for complex formation.
(ii) There is a gradual decrease in the atomic sizes of transition elements in a series with increasing atomic numbers.
(iii) Lanthanum and Lutetium do not show colouration in solutions.
(At. No : La = 57, Lu = 71)

Multiple Choice Question

10 x 1 = 10

A compound undergoes complete tetramerization in a given organic solvent. The van't Hoff factor (i) is

(a)

4.0

(b)

0.25

(c)

0.125

(d)

2.0

Pressure does not have any significant effect on solubility of solids in liquids because

(a)

solids are highly compressible

(b)

liquids are highly compressible

(c)

solubility of solid in liquid is directly proportional to partial pressure

(d)

solids and liquids are highly incompressible

The non-stoichiometric reaction:
2A + B \(\rightarrow\) C+D

Initial conc A	Initial conc of B	Initial rate (Mol L^-1)
0.1 M	0.1 M	1.2 x 10^{- 3}
0.1 M	0.2M	1.2 x 10^{- 3}
0.2 M	0.1 M	2.4 x 10^{- 3}

The rate law for formation of c is

(a)

\(\frac{\mathrm{dc}}{\mathrm{dt}}=k[\mathrm{~A}]\)

(b)

\(\frac{\mathrm{dc}}{\mathrm{dt}}=k[\mathrm{~A}][\mathrm{B}]\)

(c)

\(\frac{\mathrm{dc}}{\mathrm{dt}}=k[\mathrm{~A}]^{2}[\mathrm{~B}]^{1}\)

(d)

\(\frac{\mathrm{dc}}{\mathrm{dt}}=k[\mathrm{~A}][\mathrm{B}]^{2}\)

Across the lanthanide series, the basicity of the lanthanide hydroxides

(a)

increases

(b)

decreases

(c)

first increases and then decreases

(d)

first decreases and then increases

10.

Which element do you expect to have the highest melting point ?

(a)

(b)

(c)

(d)

11.

There are 14 elements in actinoid series. Which of the following elements does belong to this series ?

(a)

(b)

(c)

(d)

12.

Consider the decomposition of N₂O₅ as
N₂O₅ \(\longrightarrow\) 2 NO₂ + \(\frac {1}{2}\)O₂
The rate of reaction is given by
\(-\frac { d[{ N }_{ 2 }{ O }_{ 5 }] }{ dt } =\frac { 1 }{ 2 } \frac { d[{ NO }_{ 2 }] }{ dt } =2\frac { d[{ O }_{ 2 }] }{ dt } ={ k }_{ 1 }[{ N }_{ 2 }{ O }_{ 5 }]\)
Therefore, \(-\frac { d[{ N }_{ 2 }{ O }_{ 5 }] }{ dt } ={ k }_{ 1 }[{ N }_{ 2 }{ O }_{ 5 }]\)
\(+\frac { d[{ N }{ O }_{ 2 }] }{ dt } ={ k }_{ 1 }[{ N }_{ 2 }{ O }_{ 5 }]={ k }_{ 1 }'[{ N }_{ 2 }{ O }_{ 5 }]\)
\(+\frac { d[{ O }_{ 2 }] }{ dt } ={ \frac { 1 }{ 2 } k }_{ 1 }[{ N }_{ 2 }{ O }_{ 5 }]={ k }_{ 1 }''[{ N }_{ 2 }{ O }_{ 5 }]\)
Choose the correct option

(a)

\({ k }_{ 1 }={ k }_{ 1 }'={ k }_{ 1 }''\)

(b)

\({ k }_{ 1 }=2{ k }_{ 1 } '={ k }_{ 1 }''\)

(c)

\(2{ k }_{ 1 }={ k }_{ 1 }'={ k }_{ 1 }''\)

(d)

\(4{ k }_{ 1 }=2{ k }_{ 1 }'={ k }_{ 1 }''\)

13.

A solution of protein (extracted from crabs) was prepared by dissolving 0.75 g in 125 cm³ of an aqueous solution. At 4^oC, an osmotic pressure rise of 2.6 mm of the solution was observed. Then molecular weight of protein is (Assume density of solution is 1.00 g/cm³ .

(a)

\(9.4\times { 10 }^{ 5 }\)

(b)

\(5.4\times { 10 }^{ 5 }\)

(c)

\(5.4\times { 10 }^{ 10 }\)

(d)

\(9.4\times { 10 }^{ 10 }\)

14.

If x₁ and x₂ represent the mole fraction of a component A in the vapour phase and liquid mixture respectively and p_A^o and p_B^o represent vapours pressures of pure A and B, then total vapour pressure of the liquid mixture is

(a)

\(\frac { { p }_{ A }^{ o }{ x }_{ 1 } }{ { x }_{ 2 } } \)

(b)

\(\frac { { p }_{ A }^{ o }{ x }_{ 2 } }{ { x }_{ 1 } } \)

(c)

\(\frac { { p }_{ B }^{ o }{ x }_{ 1 } }{ { x }_{ 2 } } \)

(d)

\(\frac { { p }_{ B }^{ o }{ x }_{ 2 } }{ { x }_{ 1 } } \)

15.

For the reaction aA + bB \(\longrightarrow\) cC, if -3 \(\frac {d[A]}{dt} = +1.5 \frac {d[C]}{dt},\) then a, b, and c respectively are

(a)

3, 1, 2

(b)

2, 1, 3

(c)

1, 3, 2

(d)

6, 2, 3

Generic 5

4 x 5 = 20

16.

Attempt any five of the following.
(a) Ce(III) is easily oxidised to Ce(IV) Comment.
(b) E°(Mn²⁺ /Mn) is -1.18 V. Why is this value highly negative in comparison to neighbouring d-block elements?
(c) Which element of 3d-series has lowest enthalpy of atomisation and why?
(d) What happens when sodium chromate is acidified?
(e) Zn, Cd and Hg are soft metals. Why?
(f) Why is permanganate titration not carried out in the presence of HCI?
(g) The lower oxides of transition metals are basic whereas the highest are amphoteric/acidic. Given reason.

17.

(i) Name a compound of
(a) transition metal which is used in the manufacture of sulphuric acid.
(b) transition metal that is used in Haber's process for the manufacture of ammonia.
(c) transition metal that have light sensitive properties and act as valuable source in photographic industry.
(ii) Write the equations which are involved in the oxidation of hydrogen sulphide to sulphur by potassium permanganate solution.

18.

(a) Define the following terms:
(i) Ideal solution
(ii) Azeotrope
(iii) Osmotic pressure
(b) A solution of glucose (C₆H₁₂O₆) in water is labelled as 10% by weight. What would be the molality of the solution?
(Molar mass of glugose = 180 g mol^-1)

19.

Two first reactions proceed at the same rate at 15^oC when started with same initial concentration. The temperature coefficient of the first reaction is 2 while that of the second reaction is 3. What will be the ratio of the rates of these reactions at 55^oC ?

Generic 2

4 x 2 = 8

20.

Why is osmotic pressure of 1 M KCI is higher than that of IM urea solution?

21.

How many water molecules are involved in coordination in \(CuSO_{ 4 }5H_{ 2 }O\) ?

22.

Which elements are called ferrous metals ?

23.

(a) write any four differences between 'rate of reaction' and 'rate constant' of a reaction.
(b) Give any four differences between order of a reaction and its molecularity ?

Assertion and reason

4 x 1 = 4

24.

Assertion: The aqueous solution of FeCI₃ is basic in nature
Reason: FeCI₃ hydrolyses in water.
Codes:
a) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
b) Both assertion and reason are true but the reason is not the correct explanation of assertion.
c) Assertion is not true but the reason is true.
d) Both assertion and reason are false.

25.

Assertion: Water boils at 373 K as the vapour pressure at this temperature becomes equal to atmospheric pressure.
Reason: Vapour pressure of water is less than 1.013 bar at 373 K.
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.

26.

Assertion: If more and more non-volatile solute is added to a solvent, the freezing point of the solution keeps on becoming higher and higher.
Reason: Presence of large am~unt of the solid solute allow the solution to freeze more rapidly.
(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.

27.

In the following questions. an Assertion (A) is followed by a corresponding Reason (R) Use the following keys to choose the appropriate answer.
Assertion (A) A positive catalyst increases the rate of reaction.
Reason (R) A catalyst increases the rate of reaction by making available a new and more efficient mechanism.
Codes:
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A).
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

Case Study Questions

2 x 4 = 8

28.

At 298 K, the vapour pressure of pure benzene, C₆H₆ is 0.256 bar and the vapour pressure of pure toluene C₆H₅CH₃ is 0.0925 bar. Two mixtures were prepared as follows:
(i) 7.8 g of C₆H₆ + 9.2 g of toluene
(ii) 3.9 g of C₆H₆ + 13.8 g of toluene
The following questions are multiple-choice questions. Choose the most appropriate answer:
(i) The total vapour pressure (bar) of solution 1 is
(a) 0.128
(b) 0.174
(c) 0.198
(d) 0.258
(ii) Which of the given solutions has higher vapour pressure?
(a) I
(b) II
(c) Both have an equal vapour pressure
(d) Cannot be predicted
(iii) Mole fraction of benzene in vapour phase in solution 1 is
(a) 0.128
(b) 0.174
(c) 0.734
(d) 0.266
(iv) Solution I is an example of a/an
(a) ideal solution
(b) non-ideal solution with a positive deviation
(c) non-ideal solution with a negative deviation
(d) can’t be predicted

29.

The d-block of the periodic table contains the elements of the groups 3 to 12 and are known as transition elements. In general, the electronic configuration of these elements is \((n-1) d^{1-10} n s^{1-2}\). The d-orbitals of the penultimate energy level in their atoms receive electrons giving rise to the three rows of the transition metals i.e. 3d, 4d and 5d series. However Zn, Cd and Hg are not regarded as transition elements. Transition elements exhibit certain characteristic properties like variable oxidation stables, complex formation, formation of coloured ions, alloys, catalytic activity etc. Transition metals are hard (except Zn, Cd and Hg) and have a high melting point.
(a) Why are Zn, Cd and Hg non-transition elements?
(b) Which transition metal of 3d series does not show variable oxidation state?
(c) Why do transition metals and their compounds show catalytic activity?
(d) Why are melting points of transition metals high?
(e) Why is Cu²⁺ ion coloured while Zn²⁺ ion is colourless in aqueous solution?

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Answers Key:

Generic 3

5 x 3 = 15

In + 3state, Mn is unstable. It is intermediate oxidation state, so it gets reduced to more stable Mn²⁺ and oxidised to more stable higher oxidation states like Mn⁷⁺.

6.93\(\times\)10^-2 hr^-1or 1.910^-5 s^-1.

(i) \(+{1\over2}{d[NO_2F]\over dt}\)
(ii) \(-{1\over2}{d[NO_2F]\over dt}\)
(iii) \(-{d[F_2]\over dt}\)

\(\)

Given, W₂ = 3.9 s. WI = 49 g; \(\Delta T_f\)= 1.62 K
M₂(benzoic acid) = 122 g mol^-1
K_f(benzene) = 4.9 K kg mol^-1
\(\Delta T_f=\frac{i\times K_f \times W_2 \times 1000}{M_2 \times W_1}\)
\(i=\frac{\Delta T_f\times M_2 \times W_1}{K_f \times W_2 \times 1000}\)
\(i=\frac{1.62 K \times 122 g mol^{-1}\times 49 g}{4.9 K kg mol^{-1}\times 3.9 g \times 1000}\)
i = 0.50
Since, i < I, therefore solute (benzoic acid) undergoes association.

(i) It is due to the presence of vacant d-orbitals of suitable energy, the smaller size of cautions and higher charge.
(ii) It is due to increase in effective nuclear charge gradually because unpaired electrons increase in the beginning and then decreases. There is repulsion between paired electrons.
(iii) It is due to absence of unpaired electrons, they do not absorb light from visible region and do not radiate color.

Multiple Choice Question

10 x 1 = 10

(b)
0.25

(d)
solids and liquids are highly incompressible

(a)
\(\frac{\mathrm{dc}}{\mathrm{dt}}=k[\mathrm{~A}]\)

(b)
decreases

10.

(b)
W

11.

12.

13.

(b)
\(5.4\times { 10 }^{ 5 }\)

14.

(b)
\(\frac { { p }_{ A }^{ o }{ x }_{ 2 } }{ { x }_{ 1 } } \)

15.

(c) : Dividing throught by 3, we get -\(\frac {d[A]}{dt}\) = \(-\frac {1}{3} \frac {d[B]}{dt}= + \frac {1}{2}\frac {d[C]}{dt}\)

This is so for the reaction A + 3B \(\longrightarrow\) 2 C

Generic 5

4 x 5 = 20

16.

(a) Ce(III) ion have the outer electronic configuration 4 f¹5d⁰6s⁰ which can easily lose the electron from 4f orbital to acquire the stable configuration, i.e. 4f⁰5d⁰6s⁰ and form Ce(IV) ion.
(b) The E° (Mn²⁺/Mn) value is -1.18 V, which is highly negative as compared to other neighbouring d-block elements due to extra stability of half-filled orbitals of Mn²⁺ (i.e. 3d⁵).
(c) Greater is the number of unpaired electrons stronger is the resultant bonding hence greater is the enthalpy of atomisation.
In 3d series elements, Zn has the lowest enthalpy of atomisation, it is due to the absent of unpaired electrons in ns and (n - 1) d shells.
(d) When sodium chromate is acidified than orange colour solution of sodium dichromate is formed.
\(2 \mathrm{Na}_2 \mathrm{CrO}_4+2 \mathrm{H}^{+} \longrightarrow \underset{\substack{\text { Sodium dichromate } \\ \text { (Orange) }}}{\mathrm{Na}_2 \mathrm{Cr}_2 \mathrm{O}_7}+2 \mathrm{Na}^{+}+\mathrm{H}_2 \mathrm{O}\)
(e) Zn, Hg and Cd have completely filled d-orbitals in the ground state as well as in their common oxidation states. Thus, formation of strong metallic bond is not possible.
(f) Permanganate titration is not carried out in the presence of HCI because if HCl is used, the oxygen produced from the reaction of KMnO₄ and HCl is partly utilised in oxidising HCl to Cl₂, which itself acts as an oxidising agent and partially oxidises the reducing agent.
(g) In lower oxidation states, transition metals behave like metals and metal oxides are basic in nature. Thus, in lower oxidation states, transition metal oxides are basic.
As the oxidation state increases, its metallic character decreases due to decrease in size, thus, ít becomes less metallic or more non-metallic. Oxides of a non-metal may be acidic or neutral.
Thus, in higher oxidation states, transition metal oxids are amphoteric or acidic.

17.

(i) (a) Vanadium
(b) Iron
(c) Silver
(ii) \(\begin{equation} 2 \mathrm{MnO}_{4}^{-}+5 \mathrm{H}_{2} \mathrm{~S}+16 \mathrm{H}^{+} \longrightarrow 2 \mathrm{Mn}^{2+}+5 \mathrm{~S}+8 \mathrm{H}_{2} \mathrm{O} \end{equation}\)

18.

(a) (i) Ideal solution: Those solutions which follow Raoult's law at specific temperature over the entire range of concentration are called Ideal solution.
(ii) Azeotrope: A liquid mixture which distills at constant temperature without under going any changes in composition is called Azeotrope.
(iii)Osmotic pressure: The minimum excess pressure that has to be applied on the solution side to prevent the entry of the solve t into the solution through the semi-perable membrane is called osmotic pressure.
(b) Given : Mass of solute, \(\omega \) = 10 g
Mass of solvent, W = 90 g
Molar mass of solute, M = 180
\(Molality=\frac { \omega \times 1000 }{ M\times W } \)
\(=\frac { 10\times 1000 }{ 90\times 180 } \)
= 0.6172 \(\approx \) 0.62 mol kg^-1

19.

If R_I is the rate of first reaction at 25°C, then as its temperature coefficient is 2, its rate at 35°C will be = 2 R₁, at 45°C = 2 x 2 R₁ = 4 R₁ and at 55°C = 2 x 4 R₁ = 8 R₁
If R₂.is the rate of the second reaction at 25°C, then as its temperature coefficient is 3, its rate at 35°C will be = 3 R₂, at 45°C = 3 x 3 R₂ = 9 R₂ and at 55°C = 3 x 9 R₂ = 27 R₂
Also, we are given R₁ = R₂, i.e., at 25°C, the rates are equal.
At 55⁰C, \({Rate\ of\ 2nd\ reaction\over Rate\ of\ 1st\ reaction}={27R_2\over 8R_1}={27\over 8}\)

Generic 2

4 x 2 = 8

20.

1 M KCI solution dissociates into K⁺ and Cl^- therefore, its osmotic pressure is higher than that of I M solution of urea which does not dissociate.

21.

Four water molecules are coordinated to Cu²⁺ion and fifth is attached to anion by hydrogen bonding.

22.

The elements of the irst triad of Groups 8,9 and 10, i.e., iron, cobalt and nickel are called ferrous metals

23.

The important differences between Reaction rate and reaction rate constant.

S.NO	Rate of reaction	Reaction rate constant
1	It is the speed with which reactants are converted into products.It is measured as the rate of decrease of concentration of reactants or rate of increase of concentration of products with time.	It is the proportionality constant in the rate law and is defined as the rate of reaction when the concentration of the reactants is unity.
2	It depends upon the initial concentration of the reactants.	It is independent of the initial concentration of the reactants.

Order and molecularity: The important differences between order and molecularity of a reaction are given below:

S.NO	Order	Molecularity
1	Order is the sum of the powers of the concentration terms in the rate law of expression.	Molecularity is the number of reacting species undergoing simultaneous collisions in the elementary or simple reaction.
2	Order of a reaction is determined experimentally.	Molecularity is a theoretical concept.
3	Order of a reaction need not be a whole number, i.e., it can have fractional values also.	Molecularity has whole number values only, i.e., 1,2,3, etc.
4	Order of a reaction can be zero.	Molecularity of a reaction cannot be zero.

Assertion and reason

4 x 1 = 4

24.

c) Assertion is not true but the reason is true.

25.

C) Assertion is correct statement but reason is wrong statement.
Explanation:
At373 K(100∘C), the vapour pressure of water is equal to 1 atmospheric pressure which is 1.013 bar.

26.

(d): The freezing point keeps on becoming lower and lower. Depression in freezing point is a colligative property as it depends on the number of particles of the solute present in solution, so solution will freeze more rapidly on adding large amount of non-volatile solute

27.

(a) A positive catalyst increases rate of reaction by making a new and more efficient mechanism. Thus, both (A) and (R) are correct and (R) is the correct explanation of (A).

Case Study Questions

2 x 4 = 8

28.

1.(b) 0.174
2.(a) I
3.(c) 0.734
4.(a) ideal solution

29.

(a) It is because neither they nor their ions have incompletely filled d-orbitals.
(b) Scandium (Sc) and Zinc (Zn).
(c) It is because they show variable oxidation state, can form intermediate complexes and have large surface area for adsorption of gases.
(d) It is due to strong interatomic forces of attraction due to presence of unpaired electrons.
(e) It is because Cu^{2 +} has one unpaired electron and undergoes d-d transition by absorbing light from visible region and radiate blue colour, where as Zn^{2 +}is colourless due to absence of unpaired electron.