CHEM VII BRAIN TEASER

CHEMISTRY TESTLET
Name______________________________________________________
A compound, A which forms green crystals, dissolves in water to give a pale green solution. This solution gives a dirty green precipitate with sodium hydroxide solution and a white precipitate with dilute barium chloride solution acidified with dilute hydrochloric acid. When gently heated the solid A gives off water vapor (but no other gases) and forms a white powder B. When B is heated very strongly, it forms a red powder C and gives and gives off a gas that turns acidified potassium dichromate solution pale green C dissolves slowly in sulphuric acid to give a yellow solution D that forms a deep red coloration with potassium thiocyanate solution.
a) Which cation and which anion must a solution of A contain?

b) If B were dissolved in water would it form a colorless solution or pale green solution? Explain your answer
State two pieces of evidence to indicate that a reaction occurs when B is heated.


c) Solid C is found to be a metal oxide. Suggest a method that could be used to extract the metal from it.

d) Which cation must D contain?


e) The sequence of reactions from A and D must involve an oxidation process what is the evidence for this statement?



Some red crystals, known to contain the chloride anion and a metal cation (M2+), give off water vapor when gently heated, and turn blue. When dissolved in water, the crystals form a pink solution separate portions of this solution are tested as follows:
(i) Addition of dilute ammonia produces a blue precipitate that dissolves in an excess of ammonia to form a brownish yellow solution.


(ii) Addition of acidified hydrogen peroxide solution produces a black precipitate whose formula is shown to be M2O3

(iii) What else do you think the red crystals contain as well as chloride ions and M2+ ions?