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 |
Tutoring Cent
last updated 14 December 2008
