What happens when potassium chloride, potassium dichromate and concentrated sulphuric acid react?

Question

What happens when $\ce{KCl}$, $\ce{K2Cr2O7}$, and concentrated $\ce{H2SO4}$ reacts?

I have no idea how to approach these questions. I'd love if anybody can help me see the logic behind this.

Answer 1

When a mixture of $\ce{KCl}$, $\ce{K2Cr2O7}$, conc. $\ce{H2SO4}$ and heated, then they produce Chromyl chloride ($\ce{CrO2Cl2}$) , $\ce{KHSO4}$, $\ce{H2O}$ are formed. $$\ce{K2Cr2O7 +4KCl + 6H­_2SO4 → 2CrO2Cl2 +6KHSO4 + 3H2O}$$ The above reaction is commonly known as chromyl chloride test, used for testing the presence of $\ce{Cl-}$ ion in inorganic qualitative analysis.

Answer 2

Have a look at the properties of the compounds involved.

Dichromate ($\ce{Cr(VI), Cr2O7^{2-}}$) is a strong oxidant and is reduced to $\ce{Cr(III)}$ if it finds a suitable partner (which then is oxidized).

Here, a potential partner in a redox reaction is chloride: $\ce{2 Cl- + 2 e^{-} -> Cl2}$.

Answer 3

I like the question above, since it gives a general strategy.

I'll point out that mixing dichromates and sulfuric acid makes "dichromix" and there are a complicated mixture of (chromic acid)[http://en.wikipedia.org/wiki/Chromic_acid] and related compounds. Depending on pH and other factors, you can have chromates, dichromates, and even sulfur-chromate mixed ions.

At one point chromic acid was used to clean glassware, since they are very strong oxidizing agents.

SAFETY NOTE The use of chromic acid (aka "chromerge") is highly unsafe and not recommended!