The hydrolysis of iron(III) chloride

Interaction of iron(III) chloride with water

[Deposit Photos]

The hy­drol­y­sis of iron(III) chlo­ride is the cation­ic re­ac­tion of the salt with wa­ter. Cation­ic hy­drol­y­sis is pos­si­ble be­cause the salt, iron(III) chlo­ride, formed by a weak base (iron(III) hy­drox­ide Fe(OH)₃) and a strong acid (hy­drochlo­ric acid HCl). The ions from the wa­ter mol­e­cules at­tach to the cation of the hy­drox­ide, Fe³⁺.

Iron(III) chlo­ride: char­ac­ter­is­tics

Anhydrous iron(III) chloride [Wikimedia]

Iron(III) chlo­ride is a neu­tral, high­ly-sol­u­ble salt with the for­mu­la Fe­Cl₃. It is a crys­talline pow­der, and changes col­ors de­pend­ing on the an­gle of in­com­ing light (from black-brown to pur­ple, dark red, and even green in re­flect­ed light).

Af­ter hy­drol­y­sis, the salt forms a yel­low, acidic so­lu­tion.

Iron(III) chloride hexahydrate [Wikimedia]

Fe­Cl₃ is used:

  • as a cat­a­lyst of or­gan­ic syn­the­sis;
  • as a co­ag­u­lant in one of the stages of wa­ter pu­rifi­ca­tion;
  • to stain cop­per in elec­tro­plat­ing;
  • in medicine.

Click here for amaz­ing ex­per­i­ments ex­plor­ing the prop­er­ties of iron and its com­pounds.

Hy­drol­y­sis of iron chlo­ride — na­ture of the re­ac­tion

The re­ac­tion takes place in hot wa­ter. Like stan­dard hy­drol­y­sis re­ac­tions, the in­ter­ac­tion of iron(III) chlo­ride with wa­ter takes place in sev­er­al stages.

[Deposit Photos]

First, iron(III) chlo­ride dis­so­ci­ates:

Fe­Cl₃ → Fe³⁺ +3Cl⁻

Then the iron cation re­acts with wa­ter:

Fe³⁺ + НOH → FeO­H²⁺ + H⁺ (hy­drol­y­sis be­gins)

Then with an­oth­er wa­ter mol­e­cule:

FeO­H²⁺ + HOH ↔ Fe(OH)₂⁺ + H⁺

And the fi­nal stage:

Fe(OH)₂⁺ + HOH ↔ Fe(OH)₃↓ + H⁺

The hy­drol­y­sis of iron(III) chlo­ride is re­versible.