The product Bismuth (III) sulfide (

) is used as a starting material for the synthesis of other bismuth compounds. It is formed, together with an acid, from a reaction between a Bismuth (III) salt and hydrogen sulfide (

). In the given reaction, the Bismuth salt used in the reaction is Bismuth (III) chloride (

).
The balanced reaction of

and

is
Thus, the coefficient of HCl in the reaction is 6.