1.

Arsenic sulphide (As_(2)S_(3)) reacts with sulphuric acid (H_(2)SO_(4)) to form H_(3)AsO_(4) (Arsenic acid) and sulphur - dioxide (SO_(2)). What will be the coefficient of H_(2)SO_(4),H_(3)AsO_(4)andSO_(2) respectively in the balanced reaction ?

Answer»

11, 2 and 14
2, 2 and 4
11, 2 and 11
2, 2 and 3

Solution :Reaction : `As_(2)S_(3)+H_(2)SO_(4)toH_(3)AsO_(4)+SO_(2)`
(x) Oxidation Part :
(i) `As_(2)S_(3)toH_(3)AsO_(4)+SO_(2)`
(ii) `As_(2)S_(3)to2II_(3)AsO_(4)+2SO_(2)` (Balance As, S)
(iii) `underset(2(+3))underset(DARR)(As_(2))underset(+(-2)3)underset(darr)(S_(3))to2H_(3)Asunderset(2(+5))underset(darr)(O_(4))+underset((+4)3)underset(darr)(3SO_(2))`
= + 6 - 6= 10 + 12
= Zero `to` = 22
`therefore` Oxidation number is up by (22)
(y) Reduction Part :
`underset((+6))underset(darr)(H_(2)SO_(4))tounderset((+4))underset(uarr)(SO_(2))` ... (Reduction)
Oxidation no. is down by (2) in Reduction part
(z) Balance of change of oxidation number oxidation part `xx` 1 and reduction part `xx` 11
`As_(2)S_(3)to2H_(3)AsO_(4)+2SO_(2)""...(i)`
`11H_(2)SO_(4)to11SO_(2)` ... (Reduction) ...(ii)
`z(i)+z(ii)" "As_(2)S_(3)+11H_(2)SO_(4)to2H_(3)AsO_(4)+14SO_(2)`
Balancing H and O by adding `8H_(2)O` we get BALANCED redox EQUATION...
`As_(2)S_(3)+11H_(2)SO_(4)to2H_(3)AsO_(4)+14SO_(2)+8H_(2)O`
`therefore` Coefficient of `H_(2)SO_(4)` = 11
`therefore` Coefficient of `H_(3)AsO_(4)=2`
`therefore` Coefficient of `SO_(2)` = 14


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