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Does Iron react differently with dilute and concentrated hydrochloric acid? A. I know that with dilute hydrochloric acid Iron (II) chloride is formed. B. I read on the internet that with concentrated hydrochloric acid Iron reacts to form Iron (III) Chloride. Could someone tell me: 1. Is FeCl3 formed as a product of reaction between HCl (conc.) and iron? 2. If yes, then what is the complete chemical reaction?

Thank you.

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No, $\ce{FeCl3}$ is not formed upon reaction with Conc. $\ce{HCl}$. Both dilute and concentrated $\ce{HCl}$ give $\ce{FeCl2}$ as product.

$$\ce{Fe + 2HCl_{dil} -> Fe^2+ + 2Cl^- + H2 ^}$$ $$\ce{Fe + 2HCl_{conc} -> Fe^2+ + 2Cl^- + H2 ^}$$

Source: Vogel's Qualitative Inorganic Analysis

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    $\begingroup$ You want to add this statement to your answer:-"Liberation of hydrogen prevents the formation of ferric chloride". $\endgroup$
    – Nilay Ghosh
    Jul 30, 2016 at 4:58
  • $\begingroup$ @NilayGhosh why does hydrogen oppose the reaction? Can you elaborate? $\endgroup$
    – DatBoi
    Jan 20, 2021 at 9:26
  • $\begingroup$ @DatBoi Hydrogen prevents oxidation from $\ce{Fe^2+}$ to $\ce{Fe^3+}$. Refer to the previous question: "Acids can oxidize iron since the redox potentials E for pH=0 show that $\ce{H+}$ can oxidize iron to $\ce{Fe^2+}$ but non-oxidizing acids (in this case HCl) cannot further oxidize $\ce{Fe^2+}$ to $\ce{Fe^3+}$." If there is presence of oxygen, it can oxidize to $\ce{Fe^3+}$. $\endgroup$
    – Nilay Ghosh
    Jan 22, 2021 at 7:27

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