Ask A Scientist Chemistry Archive

name         Katy M.
status       student
age          15

Question -   How can you determine how hard water is? I did an
experiment to test this first I put Epsom salt in various types of
waters (they were in chemistry jars) and then I applied a drop of dish washing
detergent to each and shook it up and measured the suds level. But I am
asking how does this determine how hard the water is? or does it? Also
if one water sample was, per se, harder than another would there be a
greater amount of suds or should there be a lesser amount?
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Katy,

The harder the water, the less the sudsing. If done with care and
scrupulously clean glassware, the experiment you describe is at least an
indicator of relative hardness. You can get somewhat better results by using
a commercial hardness testing kit available wherever water softeners are
sold. In fact, most who sell water softeners will do a test for you for free
and also provide useful information to assist you in understanding the
chemistry of the test procedure.

Regards,
ProfHoff 577
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Do a web search on www.google.com on the term "water hardness kit" and you
will find a bunch of suppliers of prepared kits for testing water hardness,
as well as other substances that may be present in water.
In general, but not always, the presence of electrolytes like Epsom salts
interferes with the formation of foam, but this is not a very reliable or
sensitive way to determine water "hardness".

Vince Calder
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