............
salt17 "Prussian blue" another iron-III salt
............
Hydrochloric
acid is corrosive! Use goggles, work in a trash, ask an adult to join you.
Potassium hexacyanoferrate(II)
is another sensible indicator for iron(III) salts beside ammonium
thiocyanate.
The blue colour formed during
this test is called "Prussian blue).
* Once
again make some iron(III) solution by adding 1 ml of hydrochloric acid
(20%) to a small piece of a rusty Coal can in a vial.
* Photo 1: Take four
other vials with 0.9 ml water. Stepwise dilute the iron(III) salt solution
in the left vial: by transfer 0.1 ml of the yellow solution into
vial 2, mix, do the same with 0.1 ml of this solution etc.
* Add 1 drop of the indicator
to each of the 5 vials.
Observation
Photo
right: Blue colours appear even after a dilution of 1 to 1000.
Explanation:
Negative hexacyanoferrate(II) ions and iron(III) ions react to form the
blue iron salt
potassium iron(II) hexacyanoferrate KFe-III[Fe-II(CN)6].