Question

Arsenic estimation can be done by Bettendorff's process. The reaction is given below:
${As}_4{O}_6+{SnCl}_2+HCl\to {As}_4+{SnCl}_4+H_{2}O$
Find out the exact stoichiometric ratio of the reactants, in the order as given in question.

• A. $2,4,6$
• B. $1,6,12$
• C. $2,8,20$
• D. None of these

Answer 1

The correct option is B $1,6,12$

The correct stoichiometric coefficients can be obtained if we balance the chemical equation.
The unbalanced chemical equation is ${As}_4{O}_6+{SnCl}_2+HCl\to {As}_4+{SnCl}_4+H_{2}O$

L.H.S contains $6$ oxygen atoms. To balance oxygen atoms, the coefficient $6$ is added to water on R.H.S.

Now, R.H.S contains $12H$ atoms. To balance $H$ atoms, the coefficient $12$ is added to $HCl$ on the LHS.

Now, to balance chlorine, the coefficient 6 is added to $SnC{l}_2$ on the LHS and the coefficient $6$ is added to $SnC{l}_4$ on the RHS.

The balanced chemical equation is ${As}_4{O}_6+6{SnCl}_2+12HCl\to {As}_4+6{SnCl}_4+6H_{2}O$.

Thus, the coefficients of the reactants are $1,6$ and $12$ respectively.