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Is It A Strong or Weak or Nonelectrolyte?


Whether a compound is a strong, weak, or nonelectrolyte is completely unrelated to whether or not it is soluble.  Refer to the web page entitled “Which physical state is it? / Is it soluble?” for more information about how to tell whether a compound is soluble or not.

Of course, a compound must be soluble to be a strong or weak electrolyte, but there are also some soluble compounds which are nonelectrolytes. 

A strong electrolyte is a compound that when dissolved in water will completely ionize or dissociate into ions.  That is, the compound exists in water only as individual ions, and there are no intact molecules at all.  This solution conducts electricity well. 

A weak electrolyte is a compound that when dissolved in water only partially ionizes or dissociates into ions.  That is, the compound exists in water as a mixture of individual ions and intact molecules.  This solution conducts electricity weakly.

A nonelectrolyte is a compound that when dissolved in water does not ionize or dissociate into ions at all.  In water, this compound exists entirely as intact molecules.  The solution does not conduct electricity at all.

ACIDS are molecular compounds which ionize (turn into ions) in water.  The cation that is formed is always H1+.  Therefore, in the formulas for acids, H is always the first element listed (at least in CHE 111).  With the exception of H2S, the acids you will encounter in CHE 111 are all soluble in water.  Some acids are strong electrolytes and some acids are weak electrolytes.  There are no acids which are nonelectrolytes.  There is a list of which acids are strong ones in the textbook.  You should memorize this list.  All other acids are, by default, weak acids.

BASES can be molecular compounds or ionic compounds.  Some bases are soluble and some are not.  The soluble bases ionize or dissociate into ions in water, and the anion formed is always OH1-.  The only molecular base that you might encounter in CHE 111 is ammonia, NH3.  This is soluble in water, and is a weak electrolyte.  The ionic bases have hydroxide (OH1- ) as the anion.  If they are soluble, the ions simply separate (dissociate) in the water.  All of the ionic bases which are soluble are also strong electrolytes.  There is a list of strong bases the textbook.  You should memorize this list.

SALTS are ionic compounds which are not acids or bases.  In other words, the cation is not hydrogen and the anion is not hydroxide.  Some salts are soluble in water and some are not.  All of the salts which are soluble are also strong electrolytes (for the purposes of CHE 111).

NONELECTROLYTES are compounds which dissolve in water but do not ionize or dissociate into ions.  These would be molecular compounds other than the acids or bases already discussed.


PRACTICE EXERCISES:

Indicate for the following substances, which are all soluble in water, which type of electrolyte they are.  The choices are:  strong, weak, non.

QUESTIONS:

1. HCl   10. H2SO3
2. Cu(NO3)2   11. NaOH
3. Ba(OH)2   12. HCN
4. C6H12O6   13. COCl2
5. HNO3   14. H2C2O4
6. ZnSO4   15. Sr(OH)2
7. HBrO2   16. CaS
8. NH3   17. HClO4
9. NH4Cl   18. Na3PO4

1:00-2:00

ANSWERS (If you do not understand any of these, then re-read the above material, or go ask your instructor) :

1. strong   10. weak
2. strong   11. strong
3. strong   12. weak
4. non   13. non
5. strong   14. weak
6. strong   15. strong
7. weak   16. strong
8. weak   17. strong
9. strong   18. strong

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last updated 14 December 2008