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Su13 Detect contaminations in this gold piece by corrosive acids
Teacher experiment: The concentrated acids are very corrosive, the vapours poisonous:
..
* 4 drops of concentrated
solution of nitric acid (HNO3) are poured into a 1-ml
vial.
* 1 drop of the same
solution is added to a second 1-ml vial and mixed with 3 drops of
concentrated hydrochloric acid (HCl).
* A small sample of
very thin copper wire (Cu) is added to HNO3 in the first vial
* A small piece of
bridge
gold (Au) is added to the mixed acids in the second
vial.
Observations
Middle photo: Gas bubbles in both vials, blue colour
by Cu and brown colour by Au.
Right photo: Copper
disappears leaving a transparent blue solution. Keep it for experiment
salt 14.
The brown solution remaining
from bridge gold contains a sediment: Bridge gold is no pure substance
but a mixture.
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modification: 25.20.2001