Short Answer TypeA blackish brown coloured solid ‘A’, when fused with alkali hydroxide in presence of air produces a dark green coloured compound ‘B’. When electrolytic oxidation in alkaline medium gives a dark purple coloured compound. Identify A, B and C and write the reaction involved.
What happens when an acidic solution of the green compound ‘B’ is allowed to stand for sometime? Give the equation involved. What is the type of reaction called?
Long Answer TypeGive reasons:
(i) The d-orbital of Cu is completely filled (3d104s1) still it is considered as transition metal but Zn (3d104s2) is not.
(ii) Zinc salts are colourless at room temperature but nickel salts are coloured.
(iii) The atomic radii of europium and ytterbium do not fit into the concept of lanthanide contraction but ionic radii fit in.
(iv) The atomic radius of Cu is greater than that of Cr but ionic radius of Cr2+ is greater than that of Cu2+.
(v) Cu2+ is colourless while Cu2+ is blue in aqueous solution.
Give reasons:
(i) Scandium (At. No. 21) is a transition element but calcium (At. No. 20) is not.
(ii) The transition metal ions such as Cu+ Ag+ and Sc3+ are colourless.
(iii) The melting points of transition metals of 3d series are much higher than the melting point of zinc of the same period.
(iv) The radius of Fe2+ is less than that of Mn2+.
(v) Actinides cations are coloured.
(i) An element is called a transition element if its atom or ion has incomplete i.e., partly filled d-orbital. In scandium (1s22s22p63s23p63d14s2) the penultimate 3d orbital is partly filled and it is a transition element. In calcium (1s22s22p63s2 3p63d04s2) the 3d orbital does not contain any electron, therefore, it is not a transition element.
(ii) An ion appears colourless if it does not contain any unpaired electron in its d-orbitals.
(a) Cu+(3d104s0) is colourless because it does not contain any unpaired electron and 3d10orbital is completely filled.
(b) Ag+(14d105s10) is colourless because it does not contain any unpaired electron in its 4d-orbital and 4d10 orbital is completely filled.
(c) Sc3+ (3d04s0) is colourless because it does not contain any unpaired electron in its 3d orbital and 3d-orbital is empty.
(iii) The high values of melting points indicate that the atoms in transition metals are held together by strong metallic bonds. This is attributed to the availability of vacant d-orbitals in transition metals. This facilitates the formation of strong metallic bonds by delocalization of electron clouds in the metallic crystal lattice. In the 3d-series, Zinc has exceptionally low melting point and low boiling point, because it has completely filled d-orbitals. Therefore, the atoms in the crystal lattice of zinc are held less strongly as compared to the other members in their respective crystal lattices.
(iv) The radius of Fe2+ (1s22s22p63s23p63d64s0) is less than that of Mn2+(1s22s22p63s23p63d54s0) because in Fe2+ the electrostatic attraction between its nucleus and the outer electron clouds is stronger than that in case of Mn2+. Strong attraction causes a decrease in the distance between the nucleus and outer electron clouds.
(v) The cations of actinides are coloured because of the presence of unpaired electrons. The colour observed depends on the number of unpaired electrons. The colour is due to electronic transition within the 5f-levels.
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