Question

A.What are Lanthanide elements?
B.What do you understand by lanthanide contraction?
C.Write a chromyl chloride test with an equation.

Answer 1

Hint: F block elements are divided into two series, lanthanide and actinides. F block elements are also considered inner -transition elements. Lanthanides constitutes the first inner transition series while actinides constitutes 2nd inner-transition series.

Complete step by step answer:
A.Lanthanide elements: Lanthanides are those elements which resemble properties with lanthanum. The atomic number of lanthanide elements are from atomic number 58 to 71. Number of elements in this group is 14. Lanthanides are f-block elements. F-block elements are those elements in which the last electron enters the f subshell. This sub-shell belongs to (n-2) sub-shell. This (n-2) sub-shell is also known as antepenultimate shell.

B.Lanthanide contraction: Lanthanide contraction is defined as decrease in atomic or ionic radius with increase in atomic number of lanthanide. Reason for lanthanide contraction: The lanthanide contraction is caused by a poor shielding effect of the 4f electrons and increase in effective nuclear charge.
Consequences of lanthanide contraction:
It is difficult to separate lanthanides.
Basic strength of hydroxide of lanthanides decreases in series.
Due to lanthanide contraction the properties of the 2nd and 3rd transition series are the same.

C.Chromyl chloride test: This test is used for the detection of chloride ions i.e. Cl- ions. In this a salt containing chlorine is reacted with potassium chromate and concentrated sulphuric acid. If red fumes are given out then chromyl chloride is formed which confirms the presence of chloride ions.
Reaction involved is given below:${K_2}C{r_2}{O_7} + 4NaCl + 6{H_2}S{O_4} \to 2Cr{O_2}C{l_2} + 2KHS{O_4} + 4NaHS{O_4} + 3{H_2}O$

Note:
Chromyl chloride is a chemical compound with chemical formula $Cr{O_2}C{l_2}$. They are dark red blood colour liquid, the shape of the molecule are tetrahedral in shape. They are used as oxidising agents.