Knowing that the chemistry of lanthanoids(Ln) is dominated by its + 3 oxidation state, which of the following statements is incorrect?
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Solution
Most of the Ln3+ compounds except La3+ and Lu3+ are coloured due to the presence of f-electrons.
Amount of oxalic acid present in a solution can be determined by its titration with KMnO4 solution in the presence of H2SO4.The titration gives unsatisfactory result when carried out in the presence of HCl, because HCl
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Solution
The titration of oxalic acid with KMnO4 in presence of HCl gives unsatisfactory result because of the fact that KMnO4 can also oxidise HCl along with oxalic acid.HCl on oxidation gives Cl2 and HCl reduces KMnO4 to Mn2+
Larger number of oxidation states are exhibited by the actinoids than those by the lanthanoids, the main reason being
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Solution
The main reason for exhibiting larger number of oxidation states by actinoids as compared to lanthanoids is less erenergy difference between 5f and 6d orbitals ascompared to that between 4f and 5d orbitals.In case of actinoids we can remove electrons from 5f as well as from da nd due to this actinoids exhibit larger number of oxidation state than lanthanoids. Thus the correct answer is option (b)
Identify the incorrect statement among the following:
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Solution
4f orbital is nearer to nucleus as compared to 5f orbital therefore, shielding of 4 f is more than 5f.
Which of the following exhibit only +3 oxidation state ?
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Solution
Ac (89) = [Rn] [6d1] [7s2]
The catalytic activity of transition metals and their compounds is mainly due to :
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Solution
The transition metals and their compounds are used as catalysts. Because of the variable oxidation states they may form intermediate compound with one of the readtants. These intermediate provides a new path with lowe activation energy. V2O5 + SO2 → V2O4 + SO3
2V2O4+ O2 → 2V2O5
Four successive members of the first series of the transition metals are listed below.For which one of them the standard potential (EºM2+/M) value has a positive sign?
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Solution
E°= 0.34V
other has – ve E°R.P.
E°Co++/Co = – 0.28 V
E°Ni++/Ni= – 0.25 V
E°Fe++/Fe= – 0.44 V
Which one of the following does not correctly represent the correct order of the property indicated against it?
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Solution
The melting points of the transition element first rise to a maximum and then fall as the atomic number increases manganese have abnormally low melting point.
Which of the statements is not true?
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Solution
Na2Cr2O7 is hygroscopic.
Acidified K2Cr2O7 solution turns green when Na2SO3 is added to it. This is due to the formation of :
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Solution
The green colour appears due to the formation of Cr+++ion
\(Cr_{2}O_{7}^{2-}+3SO_{3}^{2-}+8H^{+}\rightarrow 3SO_{4}^{2-}+2Cr^{3+}+4H_{2}O\)