Calculate the oxidation number of each sulphur atom in the follow…

MCQ

Calculate the oxidation number of each sulphur atom in the following compounds :

✓
$\ce{Na_2S_2O_3}$
B
$\ce{Na_2S_4O_6}$
C
$\ce{Na_2SO_3}$
D
$\ce{Na_2SO_4}$

✓

Answer

Correct option: A.

$\ce{Na_2S_2O_3}$

Structure of $\ce{Na_2S_2O_3}$ is
$ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{S}^1\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow\\\text{Na}-\text{O}-\text{S}^2-\text{O}-\text{Na}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}$
The oxidation state of $S_1$ is $-2.$
Let oxidation state of $S_2$ be $x.$
$2\times(+1)+3(-2)+\text{x}+1\times(-2)=0\ \ \text{(For Na}) \ \ \ (\text{For O}) \ \ (\text{For coordinate S})\\+2-6+\text{x}-2=0$
Thus, the oxidation states of two $S$ atoms in $\ce{Na_2S_2O_3} $ are $-2$ and $+6.$

$\ce{Na_2S_4O_6}$

$ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ || \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\\\text{Na}-\text{O}-\text{S}^1-\text{S}^2-\text{S}^3-\text{S}^4-\text{O}-\text{Na}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ || \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ||\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{O}$
From the left, $S^1 = (-2) + (-2) + (-1) = +5$
$S^2= 0$
$S^3= 0$
$S^4= +5$

$\ce{Na_2SO_3}$

$2 \times (+1) + x + 3 \times (-2) = 0$
$x = +4$

$\ce{Na_2SO_4}$

$+2 + x + (-8) = 0$
$x = +6$

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