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 Multiple Choice QuestionsShort Answer Type

71.

Why is copper sulphate pentahydrate coloured?

 
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72. Transition metals usually form coloured ions, why?
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73. Zn, Cd, Hg compounds are usually white. Explain.
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74. Give one example of any compound in which the oxidation state of Ni is zero.
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75. Why does V2O5 act as catalyst?
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76. Transition metals form a large number of interstitial compounds. Explain.
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77. What is an alloy? Name the two types of alloy formed by transition elements. Give one example of a solid solution in relation to a smooth alloy.
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78. Give two properties in which interstitial compounds differ from its elements.
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79. What is meant by disproportionation of an oxidation state? Give an example.
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80. Cu2+ is more stable than Cu+, Explain.



Cu2+ is more stable than Cu+.Stability depends on the hydration energy (enthalpy) of the ions when they bond to the water molecules. The Cu2+ ion has a greater charge density than Cu+ ion and thus forms much stronger bonds releasing more energy. The extra energy needed for the second ionization of the copper is more than compensated for by the hydration, so much so that the Cu+ ion loses an electron to become Cu2+ which can then release this hydration energy.
In aqueous solution Cu+ disproportionate to Cu2+ and Cu
2Cu+------>Cu2+ +Cu.

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