What is silver nitrate with water

Experiment of the month
November 2009

   

Mineral water contains various dissolved ions, including chloride. This can be demonstrated by a simple precipitation reaction. It turns out that the chloride content can be very different.

Equipment and chemicals:
Test tubes, Pasteur pipettes
Mineral water, tap water
5% silver nitrate solution, 20% nitric acid.

Execution:
Test tubes with demin. Fill water, various mineral waters and tap water approx. 2-3 cm high. Add 5 drops of 20% nitric acid and shake. Add 3 drops of silver nitrate solution to each test tube. Depending on the chloride content, different amounts of a white precipitate arise, the solution with demin. Water stays clear.

Explanation:
Silver ions and chloride ions result in a white precipitate of AgCl. The addition of acid prevents silver carbonate from precipitating. Most mineral waters contain between 5 ... 100 mg / l chloride, but there are also particularly salty and particularly low-salt mineral waters.
In the example shown, the glass contains (1) demineralized water, (2) - (5) mineral water with 5/7/16/110 mg / l chloride, (6) tap water.
In tap water, the chloride content is additionally increased by chlorination, which is often carried out for disinfection.

Hazards:
Nitric acid and silver nitrate are corrosive.

Disposal:
The solutions are added to the heavy metal waste.

Literature & Links:
P. Grob: Simple school experiments on food chemistry, experiment 8.4
Inorganic Chemistry Textbooks
Information center for German mineral water


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Page created on: Saturday, October 31, 2009,A. Schunk,Charité - University Medicine Berlin.

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