Introduction: Determining an Ion Concentration Using Solubility

in chemistry many types of elements dissolve in water. Many of these elements can be harmful, and quantifying how much of these elements is in some water supplies is important. For this info graphic I will teach how to determin dissolved silver levels in water.

Step 1: How to Set Up

silver it's self as an ion dissolves in water in most cases, unless an ionic reaction occurs with another element to make it insoluble in water. Some elements when combined with others form a cloudy precipitate which can be filtered and measured. For this experiment you will need a water supply with an unknown silver concentration dissolved. For this experiment we will add our own. 1 gram of silver nitrate (AgNO3) can be dissolved in water. This ion is soluble.

Step 2: Making Your Precipitating Solution

In order to precipitate silver, it must be bound to an element that makes it undissolvable. A look at solubility chart available in all libraries, will show silver chloride (AgCl) will not dissolve in water. The reaction is shown above.

Step 3: Precipitating Silver

once a solution of NaCl is made up (because NaCl is cheep and easily dissolvable) it can be added little by little mixing throughout. No more silver is present once no cloudy precipitate is forming. The precipitate looks like the above picture.

Step 4: Filtration

The silver chloride that has resulted from the two solutions mixing can now be filter with a small round filter cut from a coffee filter and a vacuum flask shown. Remember to also weigh and write down how much the filter weighs.

Step 5: Drying

The filter paper can be dried on a watch glass in a 100 degree Celsius oven for a few hours. A typical chemical oven is shown.

Step 6: Weighing and Analysis

The filter paper is now dry and ready to be weighed. The previously recorded filter paper weight can be subtracted from the filter paper plus AgCl weight. This number can then be multiplied by the molecular ratio of silver to chloride in the molecule to get the weight of silver! You can also use this number to calculate how much you recovered compared to what was expected with chemical calculations. Solid silver chloride is shown above.

Comments

author
kymyst (author)2014-04-07

Have you actually done this ? Most sources of drinking water contain less than 5 micrograms per litre of dissolved silver. Using an ordinary laboratory analytical balance weighing to +/- 100 micrograms ( 0.0001g ), you would need to filter more than 50 litres of water even to obtain a detectable amount of silver chloride precipitate. To get a meaningful result would require more like 500 litres.

author
mrayw (author)kymyst2014-04-07

On top of that, this test is not specific for silver. For example, lead is usually present at a similar concentration and will also precipitate with chloride.

This test is usually done in reverse, with silver nitrate added to precipitate chloride. Although other ions will also precipitate with silver, chloride is usually present at a much higher concentration so any errors due to bromide, etc. are usually negligible.

author
Landamela (author)mrayw2014-04-07

This was done to convey an idea to a multi media writing class. It was done to show the general idea of solubility, but thanks anyway.

author
Landamela (author)kymyst2014-04-07

This was done to convey an idea to a multi media writing class. It was done to show the general idea of solubility, but thanks anyway.

author
jmwells (author)2014-04-06

Ok. What do I do with the silver chloride when I'm done? I'm assuming that the poisonous chlorine gas precludes heating and extracting the silver.

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