15. When a solution of silver nitrate is added to a solution of potassium chlorate no precipitate forms. How do you account for the fact that a precipitate of silver chloride is not formed? CHAPTER XXIX TIN AND LEAD ==================================================================== | | | | | | SYMBOL | ATOMIC | DENSITY | MELTING | COMMON OXIDES | | WEIGHT | | POINT | _____|________|________|_________|_________|________________________ | | | | | Tin | Sn | 119.0 | 7.35 | 235 deg. | SnO SnO_{2} Lead | Pb | 206.9 | 11.38 | 327 deg. | PbO Pb_{3}O_{4} PbO_{2} ==================================================================== ~The family.~ Tin and lead, together with silicon and germanium, form a family in Group IV of the periodic table. Silicon has been discussed along with the non-metals, while germanium, on account of its rarity, needs only to be mentioned. The other family of Group IV includes carbon, already described, and a number of rare elements. TIN ~Occurrence.~ Tin is found in nature chiefly as the oxide (SnO_{2}), called cassiterite or tinstone. The most famous mines are those of Cornwall in England, and of the Malay Peninsula and East India Islands; in small amounts tinstone is found in many other localities. ~Metallurgy.~ The metallurgy of tin is very simple. The ore, separated as far as possible from earthy materials, is mixed with carbon and heated in a furnace, the reduction taking place readily. The equation is SnO_{2} + C = Sn + CO_{2}. The metal is often purified by carefully heating it until it is partly melted; the pure tin melts first and can be drained away from the impurities. ~Properties.~ Pure tin, called block tin, is a soft white metal with a silver-like appearance and luster; it melts readily (235 deg.) and is somewhat lighter than copper, having a density of 7.3. It is quite malleable and can be rolled out into very thin sheets, forming tin foil; most tin foil, however, contains a good deal of lead. Under ordinary conditions it is quite unchanged by air or moisture, but at a high temperature it burns in air, forming the oxide SnO_{2}. Dilute acids have no effect upon it, but concentrated acids attack it readily. Concentrated hydrochloric acid changes it into the chloride Sn + 2HCl = SnCl_{2} + 2H. With sulphuric acid tin sulphate and sulphur dioxide are formed: Sn + 2H_{2}SO_{4} = SnSO_{4} + SO_{2} + 2H_{2}O Concentrated nitric acid oxidizes it, forming a white insoluble compound of the formula H_{2}SnO_{3}, called metastannic acid: 3Sn + 4HNO_{3} + H_{2}O = 3H_{2}SnO_{3} + 4NO.