Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Jules18 on October 08, 2009, 05:07:31 PM
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I'm learning about electrolytes, and my text says the general rule is that all ionic compounds are strong electrolytes.
But then it goes on to say that HF is a weak electrolyte, which confused me because I thought HF was ionic. H+ and F- are opposite ions that attract each other.
Was I wrong?
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HF is not as ionic as it may seem at first sight.
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That was a little vague.
Do you mind elaborating? My definition of an ionic bond is pretty straight-forward and simple, and HF falls under that category for me.
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It is a general rule that ionic compounds are good electrolytes, but this is because most ionic compounds completely dissolve into ions when placed in water. For example, outside of water solid sodium chloride salt (NaCl) is a non-electrolyte because the ions are all locked up in the Na-Cl bonds and can't move. In water, the salt dissolves into separate Na+ and Cl- ions. These ions can now move around separately from one another in the water and in doing so they can conduct electricity.
In contrast the H-F bond is so strong that water cannot break the H-F bond anywhere near as well as it can break the Na-Cl bond. So when you place HF in solution it largely doesn't break apart into separate H+ and F- ions; it still stays HF for the most part and HF doesn't conduct electricity. Only the H+ and F- ions are capable of providing electricity, and, since you only get a few of these ions forming, HF is considered a weak electrolyte.
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Pure liquid HF can ionize (3HF = H2F+ + HF2-).the autoprotolysis constant is equal to 10-10.7 compare to water 10-14
correction of subscripts and superscripts
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Thank you AWK, I haven't known this. I would like to remind that there are strong H bonds among HF molecules and because of this forces, HF molecules can't ionize completely.