Reaction of iron(ii), Fe2+

Colour : pale green, almost colourless.

Test Observation Notes

Add H2O2

 

Then add dilute H2SO4(aq)

 

Followed by NaOH(aq)

Solution turns from light green to yellowish brown

Intensity of yellowish-brwon colour increases

 

A red-brown ppt is formed upon addition of a few drops of NaOH(aq)

Fe2+(aq) is oxidized by hydrogen peroxide to Fe3+(aq) which is yellowish-brown

The action of hydrogen peroxide as an oxidising agent is promoted by an acid

 

Fe3+(aq) from the oxidation of Fe2+(aq) by hydrogen peroxide is precipitated as Fe(OH)3(s), which is a red-brown solid.

Add NH3(aq)

 

Leave ppt in the air for a few minutes

A green ppt is formed

 

ppt changes from green to red-brown

Fe(OH)2(s) is produced.

Fe(OH)2(s) oxidized by oxygen to red-brown Fe(OH)3(s)

Add NaOH(aq) Pale green ppt is formed insoluble in xs. The ppt slowly turns brown in air Fe3+ precipitated as Fe(OH)3(s).
Add dilute H2SO4 followed by KMnO4(aq), drop by drop KMnO4 is decolourised. A yellowish-brown solution is formed Oxidation of Fe3+ by KMnO4 to form a yellowish-green solution of Fe3+. The yellowish-brown colour observed is due to Fe3+.

 

Reaction of iron(iii), Fe3+

Colour : yellow brown to orange when unmixed with other colored cations

Test Observation Notes
Add solid NaCO3 Effervescence occurs, gas which turns limewater milky is produced. A coffee brown ppt is formed Brown ppt is formed Fe(OH)3. Fe3+ is acidic, protonate water hence carbonate is dicomposed.

Add KI(sq) followed by either;

 

Strach solution

 

Na2S2O3(aq)

Solution turns deeper brown

 

a blue black colour appears

 

Brown colour disappears leaving a pale green solution

I oxidized to brown iodine. meanwhile Fe3+ is reduced to pale green Fe2+ whose color is masked by that of iodine.

The blue black colour is due to the formation of an iodine/starch complex

 

Brown iodine is reduced by thiosuphate ions to I leaving Fe3+

 

2 Comments

author
D Change
November 19, 2023

Pretty! This was an incredibly wonderful post. Many thanks for providing this information.

Reply
author

hermosa latina ardiente sedienta de lujuria y placer deseosa de

Reply

Leave a Reply

Your email address will not be published. Required fields are marked *