1.

Which of the following statements is wrong?A. the bond angle in `H_(2)S` is `92^(@)`B. `H_(2)S` behaves both as an oxidizing as well as a reducing agentC. `H_(2)S` is a diprotic acidD. `H_(2)S` is a stronger acid than `H_(2)O`

Answer» Correct Answer - 2
Hydrogen sulphide is a powerful redcuing agent because it can readily given up its hydrogen and deposit sulphur. Thus it burns with a blue flame to form sulphur which is oxidized to sulpher dioxide,i.e, the products depend upon how much oxygen is available :
In a limited supply of air or oxygen:
`2H_(2)S(g)+O_(2)(g)rarr2H_(2)O(l)+2S(s)`
With excess of air and oxygen:
`2H_(2)S(g)+3O_(2)(g)rarr2H_(2)O(l)+3SO_(2)(g)`
It also reacts with dissolved oxygen in water so that a saturated solution of hydrogen sulphide will slowly go cloudy after standing for some days:
`2H_(2)S(aq.)+O_(2)(g)rarr2H_(2)O(l)+2S(s)`
Other reducing reactions of hydrogen sulphide included the conversion of
(i) moist chlorine to hydrogen chloride:
`H_(2)S(g)+underset("moist")(Cl_(2)(g))rarr2HCl(g)+S(s)`
(ii) mosist solution dioxide to sulpher:
`2H_(2)S(g)+underset("mosit")(SO_(2)(g))rarr2H_(2)O(l)+3S(s)`
(iii) sulphuric acid to sulpher dioxide
`H_(2)SO_(4)(l)+H_(2)S(g) rarr SO_(2)(g)+2H_(2)O(l)+S(s)`
(iv) ferric ions to ferrous ions:
`2Fe^(3+)(aq.)+H_(2)S(g) rarr 2Fe^(2+)(aq)+2H^(+)(aq)+S(s)`
(v) acidified dichromate to chromium (III) ions:
`Cr_(2)O_(7)^(2-) (aq.)+8H^(+)(aq.)+3H_(2)S(g)rarr2Cr^(3+)(aq.)+7H_(2)O(l)+3S(s)`
(vi) acidified permanganent to manganous ion `2MnO_(4)^(-) (aq.) +6H^(+)(aq) +5H_(2)S(g)rarr2Mn^(2+) (aq.)+ 8H_(2)O(l) +5S(s)`
Note that in the reaction above the hydrogen sulphide is always oxidized to sulpher. The occurrence of sulphur is in volcanic regions is attributed to the `2^(nd)` reaction as both are present in volcanic gases. Other example:
(vii) nitric acid is reduced to nitrogen dioxide:
`2HNO_(3)rarrH_(2)O+2NO_(2)+O`
`H_(2)S+OrarrH_(2)O+S`
`2HNO_(3)+H_(2)Srarr2NO_(2)+S+2H_(2)O`
(viii) ozone is reduced to dioxygen
`H_(2)S+O_(3)rarrH_(2)O+S+O_(2)`
(ix) hydrogen peroxide is reduced to water
`H_(2)O_(2)+H_(2)Srarr2H_(2)O+S`


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