I'm pretty new to chemistry and came across a last year's chemical olympiad in our country and I got stuck on this (I tried googling this problem but after a half of hour I gave up):

Will these reactions occur? If they do, what will be the products?

$$\ce{H2S + CuCl2 -> ???}$$

$$\ce{H2S + KCl -> ???}$$

In my opinion, the copper will replace the hydrogen, but I'm pretty sure the potassium won't. Am I even correct? And what's the reason behind it?

Your help is really appreciated!


Here some hints

  1. Copper and sulphur will react to form $\ce{CuS}$ and $\ce{HCl}$. The equation needs to be balanced!

I'll let you check both copper (II) sulphide and copper (II) chloride solubility in water. It might lead you to a justification for the products.

  1. Second one, no reaction.

You can make analogous reasoning for the second equation.

Some extra thoughts

In both cases: Can we understand this behaviour microscopically? Why $\ce{CuS}$ has such a low solubility compared to $\ce{CuCl2}$

Copper and sulphur ions have similar size and sulphur higher electric charge than chloride ion. So we can undestand microscopically why $\ce{CuS}$ is less soluble than $\ce{CuCl2}$.


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