Objective - Determine the percent of water
in a hydrate.
Salts are compounds composed of a metal ion plus a non metal (or
polyatomic) ion, e.g., sodium chloride (NaCl, and sodium phosphate (Na3PO4).
Hydrated salts (or Hydrates) are salts which have a definite amount
of water chemically combined.Some common hydrates are:
copper (II) sulphate pentahydrate
magnesium sulphate heptahydrate
cobalt (II) chloride hexahydrate
tin (II) chloride dihydrate
The dot indicates an attractive force between the polar water
molecules and the positively charged metal ion. On heating, the attractive forces
are overcome and the water molecules are released leaving behind the anhydrous
The water released on heating is called the water of hydration.
Since heat is absorbed during this process, the reaction is "endothermic".
(In an "exothermic" reaction heat is liberated.)
at temperatures greater than 560oC. Therefore, avoid letting the
flame of the Bunsen burner rest on one spot of the crucible. Heat
gently by holding the bunsen burner in a sweeping motion.
a black solid, CuS, is formed.