CBSE Class 12 Chemistry The d and f Block Elements Worksheet Set A

Question. Which of the following are d-block elements but not regarded as transition elements?
(a) Cu, Ag, Au
(b) Zn, Cd, Hg
(c) Fe, Co, Ni
(d) Ru, Rh, Pd
Answer. B

Question. The property which is not characteristic of transition metals is
(a) variable oxidation states.
(b) tendency to form complexes.
(c) formation of coloured compounds.
(d) natural radioactivity.
Answer. D

Question. Lanthanoid contraction is due to increase in
(a)atomic number
(b)effective nuclear charge
(c)atomic radius
(d)valence electrons
Answer. B

Question. Transition elements form alloys easily because they have
(a) Same atomic number
(b) Same electronic configuration
(c) Nearly same atomic size
(d) None of the above
Answer. C

Question. When manganese dioxide is fused with KOH in air. It gives
(a) potassium permanganate
(b) potassium manganate
(c) manganese hydroxide
(d) Mn₃O₄.
Answer. B

Question. Acidified potassium dichromate reacts with potassium iodide and oxidises it to I₂. What is the oxidation state of chromium in the products of the reaction?
(a) +4
(b) +6
(c) +3
(d) +2
Answer. C

Question. In KMnO₄ oxidation number of Mn is
(a) +2
(b) + 4
(c) + 6
(d) + 7
Answer. D

ASSERTION REASON TYPE QUESTIONS

Read the passage given below and answer the following questions:

Transition elements are elements that have partially filled d-orbitals. The configuration of these elements corresponds to (n - 1)d1-10 ns1-2. It is important to note that the elements mercury, cadmium and zinc (Ire not considered transition elements because of their electronic configurations, which corresponds to (n - 1)d1-10 ns2. Some general properties of transition elements are : These elements can form coloured compounds and ions due to d-d transition; These elements-.exhibit many oxidation states; A large variety of ligands can bind themselves to these elements, due to this, a wide variety of stable complexes formed by these ions. The boiling and melting point of these elements are high. These elements have a large ratio of charge to the radius. 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.

Question. Assertion: Tungsten has very high melting point.
Reason: Tungsten is a covalent compound.
Answer. C 

Question. Assertion: Zn, Cd and Hg are normally not considered transition metals
Reason: d-Orbitals in Zn, Cd and Hg elements are completely filled, hence these metals do not show the general characteristics properties of the transition elements
Answer. A

Question. Assertion: Copper metal gets readily corroded in acidic aqueous solution such as HCl and dil. H₂SO₄
Reason: Free energy change for this process is positive.
Answer. D 

Question. Assertion: Separation of Zr and Hf is difficult.
Reason: Because Zr and Hf lie in the same group of the periodic table.
Answer. B

SHORT ANSWERS TYPE QUESTIONS

Question. Based on the data, arrange Fe²⁺, Mn²⁺ and Cr²⁺ in the increasing order of stability of +2 oxidation state: E°Cr³⁺/Cr²⁺ = – 0.4 V, E°Mn³⁺/Mn²⁺ = 1.5 V, E°Fe³⁺/Fe²⁺ = 0.8 V
Answer. As the value of reduction potential increases, the stability of +2 oxidation state increases. Therefore, correct order of stability is Cr³⁺ | Cr²⁺ < Fe³⁺ | Fe²⁺ < Mn³⁺ | Mn2⁺

Question. (i) Name the element showing the maximum number of oxidation states among the first series of transition metals from Sc (Z = 21) to Zn (Z = 30).
Answer. Manganese (ii) Name the element which shows only +3 oxidation state. Answer. Scandium

Question. Identify the oxo anion of chromium which is stable in an acidic medium.
Answer. Cr₂0₇^2-

Question. Actinoid contraction is greater from element to element than lanthanoid contraction. Why?
Answer. This is because of relatively poor shielding by 5f electrons in actinoids in comparison with shielding of 4f electrons in lanthanoids.

Question. Assign reasons for the following: (i) Cu(I) is not known in an aqueous solution.
Answer. Because of the Lesser hydration enthalpy of Cu(I), It Is unstable in an aqueous solution and therefore, It undergoes disproportionation.

(ii) Actinoids exhibit a greater range of oxidation states than lanthanoids.
Answer. Lanthanoids show Limited number of oxidation states, such as + 2, + 3 and + 4 + 3 is the principal oxidation state). This is because of the large energy gap between 5d and 4f subshells. On the other hand, actinoids also show a principal oxidation state of + 3 but show a number of other oxidation states also. For example, uranium (Z = 92) exhibits oxidation states of + 3, + 4, + 5, + 6 and + 7 and neptunium (Z = 94) shows oxidation states of + 3, +4, + 5, + 6 and + 7. This is because of the small energy difference between 5f and 6d orbitals.

Question. Explain why the E^θ value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺.
Answer. Mn²⁺ has 3d⁵ electronic configuration. It is stable because of the half-filled configuration of the d-subshell. Therefore, Mn has a very high third ionization enthalpy for the change from d5 to d4 and it is responsible for a much more positive E^θ value for Mn³⁺/Mn²⁺ couple in comparison to Cr³⁺/Cr²⁺ and Fe³⁺/ Fe²⁺ couples.

Question. Complete the following chemical equations:
(i) Cr₂O₇²⁺+ H⁺ + I^– →
Answer. Cr₂O₇²⁺ + 6I^– + 14H⁺ → 2Cr³⁺ + 3I₂ + 7H₂O

(ii) MnO₄^– + NO₂^– + H⁺ →
Answer. 2MnO₄^– + 5N0₂^– + 6H⁺ → 2Mn2+ + 5NO₃^–+ 3H₂O

CASE BASED QUESTIONS

I. Read the following paragraph and answer to the questions given below.

The f-block elements are those in which the differentiating electrons enters the (n-2) f orbitals. There are two series of f-Block elements corresponding to filling of 4f and 5f-orbitals. The series of 4f-orbitals is called lanthanides. Lanthanides show different oxidation states depending upon stability of f0, f7 and f14 configurations, though the most common oxidation state is +3. There is a regular decrease in the size of lanthanide ions with increase in atomic number which is known as lanthanide contraction.

Question. Name a member of the lanthanide series which is well known to exhibit +4 oxidation state.
(a) Cerium (X=58) (b) Europium (Z=63)
(c) Lanthanum (Z=57)
(d) Gadolinium (Z=64)
Answer. A

Question. Identify the incorrect statement among the following.
(a) Lanthanide contraction is the accumulation of successive shrinkages.
(b) the different radii of Zr and Hf due to consequences of the lanthanide contraction.
(c) Shielding power of 4f electrons is quite weak.
(d) There is a decrease in the radii of the atoms or ions proceeds from La to Lu
Answer. B

Question. Out of the following elements, identify the one which does not show variable oxidation state.
(a) Cr
(b) Co
(c) Zn
Answer. C

Question. What is the shape of chromate ions?
(a) octahedral
(b) tetrahedral
(c) square planar
(d) pyramidal
Answer. B

Question. What is the shape of permanganate ions?
(a) octahedral
(b) tetrahedral
(c) square planar
(d) pyramidal
Answer. B

CBSE Class 12 Chemistry The d and f Block Elements Worksheet Set A 

Very Short Answer

Question. What is the position of the f- block elements in the periodic table?
Answer. The f-block elements, found in the two rows at the bottom of the periodic table.

Question. What kind of factor is responsible for exchange energy?
Answer. Exchange energy is responsible for the stabilisation of the energy state.

Question. Name the four series of the transition metals?
Answer. 3d series, 4d series, 5d series and 6d series are the four series of the transition metals

Question. What is the position of d- block elements in the periodic table?
Answer. The d-block elements are found in the middle of the period table.

Question. On what kind of parameters the thermochemical parameters are related?
Answer. The thermochemical parameters related to the transformation of the solid metal atoms.

Short Answer

Question. What do you understand by lanthanoid contraction?
Answer. The steady decrease in the size of the atoms and ions of the rare earth elements with increasing atomic number from lanthanum through lutetium is called lanthanoid contraction. It is also known as lanthanide contraction.

Question. What is the electronic configuration of the d- block?
Answer. D block Elements have a general electronic configuration of (n-1) d ^1-10ns ^1-2. These elements can find stability in half-filled orbitals and completely filled d orbitals. The (n–1) stands for the inner d orbitals which may have one to ten electrons and the outermost ns orbital may have one or two electrons.

Question. What are the factors responsible for lanthanide contraction?
Answer. The Lanthanide Contraction is caused by a poor shielding effect of the 4f electrons. Gd because as atomic number increases, the atomic radius decreases. Yb because it has a larger atomic number. Because the elements in Row 3 have 4f electrons

Question. What do you understand by the alloy formation?
Answer. Alloy Formation in d-block elements are homogeneous solid solutions of two or more metals obtained by melting the components and then cooling the melt. As transition
metals have similar atomic radii and other characteristics, hence they form alloys very readily.

Question. What do you understand by the magnetic properties of the d-blocks?
Answer. When a magnetic field is applied to the substances. There are two types of the magnetic behaviour like diamagnetism and paramagnetism. Diamagnetic substances are applied filed while the paramagnetic substances are attracted, substances which are attracted very strongly is called ferromagnetic.

Long Answer

Question. Write short note on oxidation states of the d-block?
Answer. Transition elements show variable state oxidation in their compounds. Reason of variable oxidation state is that there is a very small energy difference in between (n-1)
d and ns orbitals. As a result, electrons of (n-1) d orbitals as well as ns-orbitals take part in bond formation. Oxidation state of an element is defined as the degree of the oxidation (loss of electron) of the element in a chemical compound. Transition elements exhibit a wide variety of oxidation states in their compounds, for example: manganese shows all the oxidation states from +2 to +7 in its compounds. Oxidation results in an increase in the oxidation state. Reduction results in a decrease in the oxidation state. If an atom is reduced, it has a higher number of valence shell electrons, and therefore a higher oxidation state, and is a strong oxidant. For example, oxygen (O) and fluorine (F) are very strong oxidants. On the other hand, lithium (Li) and sodium (Na) are incredibly strong reducing agents (likes to be oxidized), meaning that they easily lose electrons. In this module, we will precisely go over the oxidation states of transition metals. It is relatively easy to lose electron(s) for transition metals compared to the alkali metals and alkaline earth metals. Alkali metals have one electron in their valence s-orbital and therefore their oxidation state is almost always +1 (from losing it) and alkaline earth metals have two electrons in their valences-orbital, resulting with an oxidation state of +2 (from losing both). This is not the case for transition metals since transition metals have 5 d-orbitals. The d-orbital has a variety of oxidation states.

Question. State the difference between lanthanoids and actinoids?
Answer. 
1. Lanthanoids are chemical elements that can be found in the lanthanide series of the f block in the periodic table of elements whereas actinoids are chemical
elements that can be found in the actinide series of the f block in the periodic table of elements.
2. Lanthanoids are non-radioactive elements except promethium whereas actinoids are radioactive elements.
3. Lanthanoids are in the lanthanide series whereas actinoids are in the actinide series.
4. Lanthanoids include elements with atomic numbers ranging from 57 to 71 whereas actinoids include elements with atomic numbers ranging from 89 to 103.
5. Lanthanoids have their valence electrons in a 4f orbital whereas actinoids have their valence electrons in a 5f orbital.

Question. State the difference between transition metals and inner transition metals?
Answer. 
1. Transition metals are chemical elements that are composed of atoms having unpaired d electrons; even their stable cations have unpaired d electrons whereas inner transition metals are chemical elements that have valence electrons in their f orbitals of the penultimate electron shell.
2. Transition metals have atomic numbers ranging from 21 to 112 whereas inner transition metals have atomic numbers ranging from 57 to 103.
3. Transition metals are in the d block of the periodic table whereas inner transition metals are in the f block of the periodic table.
4. Transition metals are abundant on earth whereas inner transition metals are less abundant on earth.
5. The most prominent oxidation state of transition metals is +2 whereas the most prominent oxidation state of inner transition metals is +3.

Question. Write short note on ionization enthalpies?
Answer. Ionisation enthalpy is the energy required to remove the most loosely bound electron from the isolated gaseous atoms to produce a cation. Those of transition elements tend to increase from left to right in the periodic table as there is an increase in nuclear charge which accompanies the filling of the inner d orbitals. However, there are some
exceptions; for example, Titanium (22) has first ionization enthalpy of 656kJ/mole whereas vanadium (23) has first ionization enthalpy of 650kJ/mole. Ionization enthalpies of transition elements show general trend of increase from left to right. However, in case of chromium (24), the change in the value of first ionization enthalpy is lower as there is no change in d orbital configuration whereas, zinc (30) shows a higher value as it represents an ionization from 4s level. ionization enthalpy for Cr and Cu are quite higher as the d5 and d10 configuration of M+ ions gets disrupted whereas, the value for Zn is correspondingly low as the ionization consists of the removal of an electron which allows the production of the stable d10 configuration. Ionization enthalpy doesn’t involve 4s orbitals and thus there is a greater difficulty for the removal of an electron from Mn2+ (d5) and Zn2+ (d10) ions. Thus, we see a marked difference between third ionization enthalpies of iron (26) and manganese (25).

Question. State the difference between d-block and f-block?
Answer. 
1. d block elements are chemical elements having electrons filled to their d orbitals whereas f block elements are chemical elements having electrons filled to their f orbitals.
2. d block elements show a wide range of oxidation states depending on their electron configurations whereas the most stable oxidation state for f block elements is +3, and there can be other oxidation states as well.
3. d block elements are known as transition elements whereas f block elements are known as inner transition elements.
4. Almost all the elements in the d block are stable whereas most f block elements are radioactive.
5. d block elements can be either transition elements or non-transition elements whereas f block elements are in two series as Lanthanides and Actinides.

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