Solubility Rules
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Solubility Rules

Solubility Rules for Ionic Compounds

You will be responsible for being able to use the solubility rules, but you will not be responsible for memorizing the solubility rules. A table of solubility rules is in your workbook as example 7. If you would like a brief explanation of what is contained in the table, read on. If the table is self-explanatory to you try your hand at exercise 8 in your workbook (also shown below) and then check your answers at the bottom of this page.

Explanation of the Solubility Rules Table

The first column lists the "type of compound" and the next two columns list which of those substances are soluble and which are insoluble or slightly soluble.

 

 

 

  Nitrates (i.e. ionic compounds containing nitrate ions), it says, are all soluble.

  Chlorides, it says, are all soluble except for some that are listed as copper(I), lead(II), mercury(I) and silver.

  All sulfates are soluble except those listed under the insoluble category.

  With hydroxides the pattern turns around. The previous pattern was that most compounds were soluble with some exceptions. With hydroxides it is the other way around. There is a short list of those that are soluble: NaOH, KOH, NH4OH, Ca(OH)2, Sr(OH)2, Ba(OH)2. The rest of them are insoluble.

  For sulfides, again there is a short list of soluble ones while the rest are insoluble.

  Again with carbonates and phosphates we have a short list of soluble ions with these polyatomic ions and all the rest are insoluble.

  Perhaps you noticed that the group 1-A metals (Na+ and K+) and ammonium ion were always listed as being soluble. So that can be another rule, and it is shown on the next line.

Solubility Rules for Ionic Compounds:

(Also shown in example 7 in your workbook.)

Type of compound

Soluble

Insoluble or
Slightly Soluble {ss}

Nitrates All ---
Chlorides All except those listed as insoluble Copper(I)
Lead(II) {ss}
Mercury(I)
Silver
Sulfates All except those listed as insoluble Strontium
Barium
Calcium {ss}
Silver {ss}
Lead(II)
Hydroxides Sodium
Potassium
Ammonium
All except those listed as soluble,
Calcium {ss}
Strontium {ss}
Barium {ss}
Sulfides Ammonium
Group IA metals
Group IIA metals
All except those listed as soluble
Carbonates & Phosphates Ammonium
Group IA metals
All except those listed as soluble
Ammonium & Group IA metals All ---

 

 

Practice Using the Solubility Rules

Now you should use these solubility rules to decide whether or not some compounds are soluble. So take some time now to determine whether the following compounds are soluble or insoluble. (These are also listed in exercise 8 in your workbook.) After you have done that, check your answers below.

NaOH Fe2S3 MgSO4 PbCl2 Ba(NO3)2 MgCO3

 

Answers

NaOH Fe2S3 MgSO4 PbCl2 Ba(NO3)2 MgCO3
soluble insoluble soluble insoluble soluble insoluble

Note that Fe2S3 is a sulfide rather than a sulfate.

 

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