SCH4C                                     Introduction to Qualitative Analysis

General Solubility Rules

1. The nitrates, chlorates, and acetates of all the metals are soluble in water.  Silver acetate is sparinngly soluble.
 
2. All sodium, potassium and ammonium salts are soluble in water.
 
3. The chlorides, bromides, and iodides of all the metals except silver, lead and mercury(I); are soluble in water.  Mercury(II) iodide is insoluble in water.  The lead halides are soluble in hot water.  The water insoluble halides are also insoluble in dilute acids.
 
4. The sulphates of all metals except lead(I); and lead(II), merucry(I), barium and calcium are soluble in water.  Silver sulphate is slightly soluble.
 
5. The carbonates, phosphates, borates, sulphites, chromates, and arsenates of all metals except sodium, potassium, and ammonium are insoluble in water, but soluble in dilute acids.  Magnesium chromate is soluble in water, magnesium is very slightly soluble in water.
 
6. The sulphides of all metals except barium, calcium, magnesium, sodium, potassium and ammonium are insoluble in water.  The sulphides or iron, cobalt, nickel, zinc, and manganese are soluble in, or will not precipitate from, dilute acid solutions of 0.3 M H3O1+.
 
7.  The hydroxides of soodium, potassiujm and ammonium are very soluble in water.  The hydroxides of calcium and barium are moderately soluble.  The oxides and hydroxides of all other metals are insoluble.
      From a study of the General Solubility Rules above many schemes for the separating of the cations into groups could be formulated on the basis of the solubility of their various salts.
      You do not have to do this since it has already been done for you.  In the following pages are outlined a scheme, along with all the reasons and reactions for usch a scheme.
     To help you rememeber the General Solubility Rules here is the solubility song......
Potassium, sodium and ammonium salts,
    Whatever they may be,
Can always be depended on,
     For solubility.
When asked about the nitrates,
     The answer's always clear,
They each and all are soluble,
     Is what we want to hear.
Most every chloride's soluble,
     At least we've always read,
Save silver, mercurous mercury,
     And (slightly) chloride of lead.
Every single sulphate,
     Is soluble, 'tis said,
'Cept barium and calcium,
     And strontium and lead.
Hydroxides of metals won't dissolve,
     That is, all but three,
Potassium, sodium and ammonium,
     Dissolve quite readily.
And then you must remember,
     That you must not forgit,
Calcium and barium,
     Dissolve a little bit.
Metallic sulphides will not mix,
     With water it is true,
But if you read the two above,
     You'll find out which ones do.
The carbonates, insoluble,
     It's lucky that it's so,
Or else our marble buildings,
    Would melt away like snow.
(Repeat with feeling)
Potassium, sodium and ammonium salts,
    Whatever they may be,
Can always be depended on,
     For solubility.

 


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Copyright 1997, 2002, 2003  Tom Stretton (stretton@ripnet.com) Updated August, 2002 ts.