Question

(a) What are Lanthanide elements?
(b) What do you understand by Lanthanide contraction?
(c) Write chromyl chloride test with equation.

Answer 1

(a) Lanthanide elements: Lanthanides are elements which resemble very much in properties with lanthanum. Lanthanide is group of $14$ elements from atomic number $58$ to $71$. In these elements on increasing atomic number electron enters into $f$-sub-shell of the atom. This sub-shell belongs to $(n-2)$ i.e., antipenultimate shell hence these elements are also called $f$-block elemetns.
(b) Lanthanide contraction: Decrease in atomic or ionic radii with increase in atomic number of lanthanides is called lanthanide contraction.
(c) Chromyl Test: Chloride radical is detected by this test. In chromyl chloride test, chromyl chloride gas (orange red colour is produced on heating the salt with solid $K_2{Cr}_2{O}_7$ and conc. $H_{2}S{O}_4$.
$4NaCl+K_2{Cr}_2{O}_7+6H_{2}S{O}_4\to 4NaHS{O}_4+2KHS{O}_4+3H_{2}O+2Cr{O}_2{Cl}_2$
(Orange-red gas)