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(a). Chemistry of all the lanthanoids is...

(a). Chemistry of all the lanthanoids is quite similar.
(b). The actinide contraction differs from lanthanide contraction? Explain
(c). A serious accident occurred in a chemistry laboratory when a student tried to dissolve excess of `KMnO_4` in conc. `H_2SO_4`.

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(a). The change in the size of the lanthanoids due to lanthanoid contraction is very small as we proceed from `La(Z=57)` to `Lu(Z=71)`. Hence, their chemical properties are similar. Moreover their valence shell configuration remains the same because the electron are added into the inner 4f-subshell. Hence, they show similar chemical properties.
(b). Lanthanide contraction refers to the gradual decrease in the size of the anthanoids and their trivalent ions. `(Z=58` to 71) whereas actinoid series refers to the gradual decrease in the size of the actinoids or their ions `(M^(3+)` or `M^(4+))(Z=90` to 103). They differ in the fact that in the actinoid series, the contraction is greater from element to element due to poor shielding by 5f electrons than by 4f electrons.
(c). This is due to the formation of high explosive oily substance `Mn_2O_7` which is responsible for the accident
`2KMnO_4+H_2SO_4toK_2SO_4+Mn_2O_7+H_2O`
`2Mn_2O_7overset(Explodes)to4MnO_2+3O_2`
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(a) Give preparation of potassium permanganate (KMnO_4) . (b) What is lanthanoid contraction, give its cause. (c ) Transition metals show catalytic properties. Explain.

(a) What is meant by the term lanthanoid contraction ? What is it due to and what consequences does it have on the chemistry of elements following lanthanoids in the periodic table ? (b) Explain the following observations : (i) Cu^(+) ion is unstable in aqueous solutions . (ii) Although Co^(2+) ion appears to be stable , it is easily oxidised to Co^(3+) ion in the presence of a strong ligand. (iii) The E_(Mn^(2+)//Mn)^(@) value for manganese is much more than expected from the trend for other elements in the series.

Give reason for the following : (a) Conc. H_2 SO_4 cannot be used for drying H_2 . (b) KMnO_4 should not be dissolved in conc. H_2 SO_4 .

The f-block elements are those in which the differentiating electron enters the (n-2)f orbital. There are two series of f-block elements corresponding to filling of 4f and 5f-orbitals called lanthanides and actinides respectively. They show different oxidation states depending upon the stability of f^0, f^7 and f^14 configurations, though the principal oxidation state is +3. There is a regular decrease in size of lanthanide ions with increase in atomic number and it is known as lanthanide contraction. As a result of this, the basic character of oxides and hydroxides decreases from first element (La) to last element (Lu). All the actinides are radioactive and therefore, it is difficult to study their chemical nature. Which of the following statements is not true ?

The f-block elements are those in which the differentiating electron enters the (n-2)f orbital. There are two series of f-block elements corresponding to filling of 4f and 5f-orbitals called lanthanides and actinides respectively. They show different oxidation states depending upon the stability of f^0, f^7 and f^14 configurations, though the principal oxidation state is +3. There is a regular decrease in size of lanthanide ions with increase in atomic number and it is known as lanthanide contraction. As a result of this, the basic character of oxides and hydroxides decreases from first element (La) to last element (Lu). All the actinides are radioactive and therefore, it is difficult to study their chemical nature. Ce (Z = 58) and Yb (Z = 70) exhibit stable +4 and +2 oxidation states respectively. This is because

The f-block elements are those in which the differentiating electron enters the (n-2)f orbital. There are two series of f-block elements corresponding to filling of 4f and 5f-orbitals called lanthanides and actinides respectively. They show different oxidation states depending upon the stability of f^0, f^7 and f^14 configurations, though the principal oxidation state is +3. There is a regular decrease in size of lanthanide ions with increase in atomic number and it is known as lanthanide contraction. As a result of this, the basic character of oxides and hydroxides decreases from first element (La) to last element (Lu). All the actinides are radioactive and therefore, it is difficult to study their chemical nature. The atomic numbers of three lanthanide elements X,Y and Z are 65,68 and 70 respectively. The basic character of their hydroxides will decrease as

The f-block elements are those in which the differentiating electron enters the (n-2)f orbital. There are two series of f-block elements corresponding to filling of 4f and 5f-orbitals called lanthanides and actinides respectively. They show different oxidation states depending upon the stability of f^0, f^7 and f^14 configurations, though the principal oxidation state is +3. There is a regular decrease in size of lanthanide ions with increase in atomic number and it is known as lanthanide contraction. As a result of this, the basic character of oxides and hydroxides decreases from first element (La) to last element (Lu). All the actinides are radioactive and therefore, it is difficult to study their chemical nature. Terbium has the electronic configuration : [Xe]5f^(9) 6s^2 . It will show oxidation states of

(a) Complete the following chemical equations for reactions : (i) MnO_(4(aq))^(-) + S_(2)O_(3(aq))^(2-) + H_(2)O_((l)) to (ii) Cr_(2)O_(7 (aq))^(2-) + H_(2)S_((g)) + H_((aq))^(+) to (b) Give an explanation for each of the following observations : (i) The gradual decrease in size (actinoid contraction) from element to element is greater among the actinoids than that among the lanthanoids (lanthanoid contraction.) (ii) The greatest number of oxidation states are exhibited by the members in the middle of a transition series. (iii) With the same d-orbitals configuration (d^(4)) Cr^(2+) ion is a reducing agent but Mn^(3+) ion is an oxidising agent .

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