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प्रश्न
Describe the oxidising action of potassium dichromate and write the ionic equation for its reaction with H2S.
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उत्तर
Potassium dichromate acts as a strong oxidising 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)
H2S is oxidised to sulphur.
\[\ce{Cr2O^2-_7 + 8H^+ + 3H2S -> 2Cr^3+ + 7H2O + 3S}\]
संबंधित प्रश्न
The elements of 3d transition series are given as: Sc Ti V Cr Mn Fe Co
Answer the following: Write the element which shows maximum number of oxidation states. Give reason.
Why do the transition elements have higher enthalpies of atomisation?
To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.
How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.
Predict which of the following will be coloured in the aqueous solution?
Ti3+, V3+, Cu+, Sc3+, Mn2+, Fe3+ and Co2+. Give reasons for each.
Which one of the following ions is coloured?
The paramagnetic character in the 3d-transition series elements increases up to Mn and then decreases.
How is potassium dichromate prepared from chrome iron ore?
Explain why Zn2+ salts are white whereas Cu2+ salts are coloured.
Transition metals with highest melting point is ____________.
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.
Explain why does colour of KMnO4 disappear when oxalic acid is added to its solution in acidic medium.
The halides of transition elements become more covalent with increasing oxidation state of the metal. Why?
The standard electrode potentials of four elements A, B, C and D are – 3.05, – 1.66, – 0.40 and + 0.80. The highest chemical reactivity will be exhibited by
Why are all copper halides known except that copper iodide?
Give reason for the following statement:
Physical and chemical properties of the 4d and 5d series of the transition elements are quite similar to expected.
Give two similarities in the properties of Sc and Zn.
