Write a net ionic equation for the reaction that occurs when zinc sulfide and excess hydroiodic acid are combined.

Question

Write a net ionic equation for the reaction that occurs when zinc sulfide and excess hydroiodic acid are combined. Include phases (g,I, aq,s)

Answer 1

Hello Hussein

 

As per the solubility rules, zinc sulfide (ZnS) is an insoluble ionic compound.  When sulfides react with acids, they form hydrogen sulfide (H₂S) gas as one of the products.  From this information, you can write the molecular equation as:

 

ZnS (s)  +  2 HI (aq)   --->   ZnI₂ (aq)  +  H₂S (g)

 

Hydroiodic acid is a strong acid, and will ionize to form H⁺ and I^- ions in an aqueous solution.  Hence, the ionic equation is:

 

ZnS (s) + 2 H⁺ (aq)  +  2 I^- (aq)  --->  Zn²⁺ (aq)   +   2 I^- (aq)  +  H₂S (g)

 

From the ionic equation, you can see that the iodide ion (I^-) is a spectator ion, and you can therefore, cancel it from the reactant and product side of the equation giving the net ionic equation as follows:

 

ZnS (s) + 2 H⁺ (aq)  ---> Zn²⁺ (aq)  +  H₂S (g)