Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
-----------------
hydrochloric acid : HCl
nitric acid : HNO3
hydroxyl amine sulfate : (NH3OH)2 SO4
sodium citrate : COONa CH2 COH(COONa) CH2 COONa
tetrachloro auric acid : HAuCl4 . 2H2O
Class:
------
elem=Au
redox
Summary:
--------
Tetra chloro auric acid (a.k.a. "gold chloride"), a gold (III) compound is
easily reduced to metallic gold, which forms a colloidal solution. With
strong reductors, the gold particles formed are so large that they form
a dark precipitate.
Description:
------------
Add a drop of a solution of a 1% by weight solution of tetrachloro auric acid
to a solution of sodium citrate: The liquid becomes pale yellow and remains
clear. After a few minutes it has turned grey/blue and still looks clear.
Add a little amount of hydroxyl amine sulfate: The liquid becomes a little
turbid. After 1 day, the liquid is colorless and clear and there are a few
dark black spongy particles at the bottom.
Decant the colorless liquid, rinse with water (repeat a few times) and keep
the black particles. Add some HNO3 (appr. 50% by weight) to the black
particles: No reaction occurs. The particles do not dissolve.
Add some HCl (30% by weight): The particles now quickly dissolve and an
intense yellow compound is formed. This compound dissolves and makes the
entire liquid pale yellow. While the solid dissolves, no gas is evolved.
Add some solid hydroxyl amine sulfate: The solid dissolves, no further
visible changes (probably the amount added was too small).