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The d-and f-Block Elements — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe d-and f-Block Elements2 Marks
Question
Explain chemical reactivity of transition metals.
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Answer

$\rightarrow$ Transition metals vary widely in their chemical reactivity.
$\rightarrow$ Many of them are sufficiently electropositive to dissolve in mineral acids, although a few are 'noble' $-$ that is, they are unaffected by simple acids.
$\rightarrow$ The metals of the first series with the exception of copper are relatively more reactive and are oxidised by $1M H+,$ though the actual rate at which these metals react with oxidising agents like hydrogen ion $(H+)$ is sometimes slow
$\rightarrow$ The $E^\circ$ values for $M^{2+}/M$ indicate a decreasing tendency to form divalent cations across the series
$\rightarrow$ This general trend towards less negative $E^\circ$ values is related to the increase in the sum of the first and second ionization enthalpies.
$\rightarrow$ It is interesting to note that the $E ^{\ominus}$ values for $Mn , Ni$ and $Zn$ are more negative than expected from the general trend.
$\rightarrow$ An examination of the $E ^{\ominus}$ values for the redox couple $M ^{3+} / M ^{2+}$ shows that $Mn ^{3+}$ and $Co ^{3+}$ ions are the strongest oxidising agents in aqueous solutions. The ions $Ti ^{2+}, V ^{2+}$ and $Cr ^{2+}$ are strong reducing agents and will liberate hydrogen from a dilute acid, e.g.,
$2 Cr ^{2+}( aq )+2 H ^{+}( aq )  \rightarrow  2 Cr ^{3+}( aq )+ H _2(g)$

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