\(K_2Cr_2O_7\) paper acidified with dil. \(H_2SO_4\) turns green when exposed to :
Show Hint
The reduction of \(K_2Cr_2O_7\) by SO2 produces Cr3+ ions, which impart a green colour to the solution.
Sulphur dioxide
Sulphur trioxide
Carbon dioxide
Hydrogen sulphide
The Correct Option is A
Solution and Explanation
When \(K_2Cr_2O_7\) is acidified with dilute \(H_2SO_4 \)and exposed to\( SO_2\), it gets reduced, turning green due to the formation of\( Cr^3+\) ions:
\(Cr_2O ^{2−} _7 + 3SO_2 + 2H ^+ → 2Cr^{3+} + 3SO^{2−}_ 4 + H_2O\).
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Concepts Used:
d block elements
The elements, in the columns of the periodic table in which d subshells are being occupied are known as d block elements.
These are the elements that have the capability of forming stable cations with incompletely filled d orbitals. Elements like mercury and Zinc are not considered transition metals because they have electronic configurations: (n-1)d10 ns2. These elements have filled d-orbitals in their ground state and, therefore, even in some of their oxidation states.
General Properties Of d-Block Elements
- Multiple oxidation states- The oxidation states of d block elements show very few energy gaps; therefore, they exhibit many oxidation states. Also, the energy difference between s and d orbital is very less. Therefore both the electrons are involved in ionic and covalent bond formation, which ultimately leads to multiple oxidation states.
- Formation of complex compounds- Ligands show a binding behaviour and can form so many stable complexes with the help of transition metals. This property is mainly due to:
- Availability of vacant d orbitals.
- Comparatively small sizes of metals.
- Hardness- Transition elements are tough and have high densities because of the presence of unpaired electrons.
- Melting and boiling points- Melting and boiling points of transition are very high. This is because of the presence of unpaired electrons and partially filled d orbitals. Because of these two things, they form strong bonds and therefore have high melting and boiling points.
- Atomic radii- The atomic and ionic radius of the transition elements decreases as we move from Group 3 to group 6. However, it remains the same between group 7 and group 10, and from group 11 to group 12 increases.
- Ionization enthalpy- The ionization enthalpies of the transition elements are generally on the greater side as compared to the S block elements