(see kipp’s apparatus). Solutions in
water (known as hydrosulphuric acid)
contain the anions HS–and minute
traces of S2–and are weakly acidic.
Acid salts (those containing the HS–
ion) are known as hydrogensulphides
(formerly hydrosulphides). In acid so-
lution hydrogen sulphide is a mild
reducing agent. Hydrogen sulphide
has an important role in traditional
qualitative chemical analysis, where
it precipitates metals with insoluble
sulphides. Hydrogen sulphide is ex-
ceedingly poisonous (more toxic than
hydrogen cyanide). See also claus
process.
hydrogensulphite (bisulphite)A
salt containing the ion –HSO 3 or an
ester of the type RHSO 3 , where R is
an organic group.
hydroiodic acid See hydrogen io-
dide.
hydrolysis A chemical reaction of a
compound with water. For instance,
salts of weak acids or bases hydrolyse
in aqueous solution, as in
Na+–CH 3 COO–+ H 2 O ˆNa++ OH–+
CH 3 COOHThe reverse reaction of *esteriÜca-
tion is another example. See also
solvolysis.
hydromagnesite A mineral form
of basic *magnesium carbonate,
3MgCO 3 .Mg(OH) 2 .3H 2 O.
hydron The positive ion H+. The
name is used when it is not relevant
to specify the isotope, as is usually
the case in compounds in which the
hydrogen is in natural abundance.
When the isotope is relevant then
proton (^1 H+), deuteron (^2 H+), or triton
(^3 H+) should be used.
hydronium ion See oxonium ion.
hydrophilic Having an afÜnity for
water. See lyophilic.
hydrophobic Lacking afÜnity for
water. See lyophobic.hydroquinone See benzene-1,4-
diol.
hydrosol A sol in which the contin-
uous phase is water. See colloids.
hydrosulphate See hydrogensul-
phate.hydrosulphide See hydrogen sul-
phide.hydrosulphuric acid See hydro-
gen sulphide.
hydroxide A metallic compound
containing the ion OH–(hydroxide
ion) or containing the group –OH (hy-
droxyl group) bound to a metal atom.
Hydroxides of typical metals are
basic; those of *metalloids are am-
photeric.
hydroxoacid A type of acid in
which the acidic hydrogen is on a hy-
droxyl group attached to an atom
that is not attached to an oxo (=O)
group. An example is
Si(OH 4 ) + H 2 O →Si(OH) 3 (O)–+ H 3 O+
Compare oxoacid.hydroxonium ion See oxonium
ion.4-hydroxybutanoic acid
(gammahydroxybutyric acid; GHB) A
naturally occurring carboxylic acid,
HO(CH 2 ) 3 COOH, found in small
amounts in most living things. It is
used as a therapeutic drug to treat in-
somnia, depression and alcoholism.
GHB, as it is commonly known, is
also used as an illegal club drug and
as a date-rape drug.279 4-hydroxybutanoic acid
h
OH
C
H 2
C
H 2
C
H 2
OH
O
4-hydroxybutanoic acid