Modern inorganic chemistry

170 GROUP IV

tin gives a solution of tin(II) chloride, there being no further oxida-

tion to the + 4 oxidation state :

Sn + 2HCl^SnCl 2 4- H 2 |

Concentrated nitric acid, however, is an oxidising agent and tin

reacts to give hydrated tin(IV) oxide in a partly precipitated, partly

colloidal form, together with a small amount of tin(II) nitrate,

Sn(NO 3 ) 2 :

Sn + 4HNO 3 -> SnO 2 i + 4NO 2 + 2H 2 O

A similar oxidation reaction occurs with concentrated sulphuric
acid but in this case hydrated tin(IV) ions remain in solution :

Sn + 4H 2 SO 4 -> Sn(SO 4 ) 2 + 4H 2 O -f 2SO 2 t

Lead

Lead reacts only briefly with dilute hydrochloric and sulphuric acids
for both lead(II) chloride and lead(II) sulphate are insoluble and
form a film on the lead which effectively prevents further attack.
Lead, however, does slowly dissolve in both concentrated sulphuric
and hydrochloric acids. The sulphuric acid is reduced to sulphur
dioxide :

Pb -f 2H 2 SO 4 -> PbSO 4 -f 2H 2 O + SO 2 T

Lead reacts slowly with hot concentrated hydrochloric acid since
the lead(II) chloride dissolves in an excess of the hot hydrochloric
acid to form the acid H 2 [Pb"Cl 4 ]:

Pb -f 4HC1 -> H 2 [PbCl 4 ] + H 2 f

Again, nitric acid readily dissolves lead but is unable to oxidise lead
beyond the oxidation state -f 2. The reduction products of the nitric
acid vary with the concentration of acid used, and a number of
nitrogen oxides are usually obtained. Warm dilute nitric acid gives
mainly nitrogen oxide, NO,

3Pb -f 8HNO 3 -> 3Pb(NO 3 ) 2 -f 4H 2 O +

whilst cold concentrated acid gives mainly nitrogen dioxide, NO 2 :

Pb 4- 4HNO 3 -> Pb(NO 3 ) 2 + 2H 2 O + 2NO 2 t