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प्रश्न
Describe the oxidising action of potassium dichromate and write the ionic equation for its reaction with iron (II) solution.
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उत्तर
Potassium dichromate acts as a strong oxidizing agent. It is used as a primary standard in volumetric analysis. The oxidation action of dichromate ion in an acidic medium can be represented as follows:
\[\ce{Cr2O^{2-}_7 + 14H^+ + 6e^- -> 2Cr^{3+} + 7H2O}\] (E– = 1.33 V)
When ferrous salts (Fe2+) are treated with acidified K2Cr2O7, they are oxidised to ferric (Fe3+) salts.
\[\ce{Cr2O^2-_7 + 14H^+ + 6Fe^2+ -> 2Cr^3+ + 7H2O + 6Fe^3+}\]
संबंधित प्रश्न
Account for the following:
Cr2+ is a strong reducing agent.
The `E_((M^(2+)//M))^Θ` value for copper is positive (+0.34 V). What is possibly the reason for this? (Hint: consider its high ΔaHΘ and low ΔhydHΘ)
Explain why Cu+ ion is not stable in aqueous solutions?
What may be the stable oxidation state of the transition element with the following d electron configurations in the ground state of its atom?
3d3
How would you account for the following:
Cobalt (II) is stable in aqueous solutions, but in the presence of complexing reagents, it is easily oxidised.
Give reasons:
E° value for the Mn3+/Mn2+ couple is much more positive than that for Fe3+/Fe2+.
Account for the following :
Ti4+ is colourless whereas V4+ is coloured in an aqueous solutions.
Explain why Mn2+ is more stable than Fe2+ towards oxidation to +3 state. (At. no. of Mn = 25, Fe = 26)
Which among the following transition metal has the lowest melting point?
Read the passage given below and answer the following question:
The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.
In the following questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage.
Assertion: Transition metals form protective oxide films.
Reason: Oxides of transition metals are always stoichiometric.
When \[\ce{KMnO4}\] solution is added to oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time because ______.
Why first ionisation enthalpy of Cr is lower than that of Zn?
Answer the following question:
Which element of the first transition series has highest second ionisation enthalpy?
Which of the following is non-metallic?
Catalytic hydrogenation of benzene gives
The spin magnetic moment of cobalt in the compound Hg [Co(SCN)4] is:-
The complex showing a spin-span magnetic moment of 2.82 B.M. is :-
Which of the following species has maximum magnetic momentum?
Give a reason for the following:
Transition metals possess a great tendency to form complex compounds.
Why are interstitial compounds well known for transition metals?
