stable equilibriumSee equilib-
rium.
staggered See conformation.
staggered conformation See con-
formation.
stainless steelA form of *steel
containing at least 11–12% of
chromium, a low percentage of car-
bon, and often some other elements,
notably nickel and molybdenum.
Stainless steel does not rust or stain
and therefore has a wide variety of
uses in industrial, chemical, and do-
mestic environments. A particularly
successful alloy is the steel known as
18–8, which contains 18% Cr, 8% Ni,
and 0.08% C.
stalactites and stalagmitesAc-
cretions of calcium carbonate in
limestone caves. Stalactites are taper-
ing cones or pendants that hang
down from the roofs of caves; stalag-
mites are upward projections from
the caveÛoor and tend to be broader
at their bases than stalactites. Both
are formed from drips of water con-
taining calcium hydrogencarbonate
in solution and may take thousands
of years to grow.
standard cell A voltaic cell, such
as a Clark cell, or *Weston cell,
used as a standard of e.m.f.
standard electrode An electrode
(a half cell) used in measuring elec-
trode potential. See hydrogen half
cell.
standard electrode potential See
electrode potential.
standard solution A solution of
known concentration for use in volu-
metric analysis.
standard state A state of a system
used as a reference value in thermo-
dynamic measurements. Standard
states involve a reference value of
pressure (usually one atmosphere,
101.325 kPa) or concentration (usu-
ally 1 M). Thermodynamic functions
are designated as ‘standard’ when
they refer to changes in which reac-
tants and products are all in their
standard and their normal physical
state. For example, the standard
molar enthalpy of formation of water
at 298 K is the enthalpy change for
the reaction
H 2 (g) + ½O 2 (g) →H 2 O(l)
∆HŠ 298 = –285.83 kJ mol–1. Note the
superscript Šis used to denote stan-
dard state and the temperature
should be indicated.standard temperature and pres-
sure See s.t.p.stannaneSee tin(iv) hydride.stannateA compound formed by
reaction of tin oxides (or hydroxides)
with alkali. Tin oxides are ampho-
teric (weakly acidic) and react to give
stannate ions. Tin(IV) oxide with
molten alkali gives the stannate(IV)
ion
SnO 2 + 2OH–→SnO 3 2–+ H 2 O
In fact, there are various ions present
in which the tin is bound to hydrox-
ide groups, the main one being the
hexahydroxostannate(IV) ion,
Sn(OH) 6 2–. This is the negative ion
present in crystalline ‘trihydrates’ of
the type K 2 Sn 2 O 3 .3H 2 O.
Tin(II) oxide gives the trihydroxo-
stannate(II) ion in alkaline solutions
SnO(s) + OH–(aq) + H 2 O(l) →
Sn(OH) 3 – (aq)
Stannate(IV) compounds were for-
merly referred to as orthostannates
(SnO 4 4–) or metastannates(SnO 3 2–).
Stannate(II) compounds were called
stannites.
stannic compoundsCompounds
of tin in its higher (+4) oxidation
state; e.g. stannic chloride is tin(IV)
chloride.501 stannic compounds
s