GROUP VI 309
(a) Na 2 O dissolves in water to give an alkaline solution: C1 2 O
dissolves in water to give an acidic solution.
(b) C1 2 O is a gaseous oxide, its molecule being V-shaped: Na 2 O
is an ionic compound which has an infinite 3-dimensional
lattice structure.
(c) A1 2 O 3 forms a hydrated oxide which is basic, but the addition
of alkali produces a solution containing the aluminate anion,
A1O2-
(d) SiO 2 and CO 2 are both acidic oxides. SiO 2 is a solid of high
melting-point, whereas CO 2 is a gas.
(e) N 2 O is a gaseous, neutral oxide, its molecule being linear.
(CA)
- Give an explanation of the following observations:
(a) An aqueous solution of sodium sulphide smells of hydrogen
sulphide.
(b) When hydrogen sulphide is bubbled through an acidified
solution of a cobalt(II) salt, no precipitate is formed, but a black
precipitate is produced when the solution is made slightly
alkaline.
(c) When hydrogen sulphide is bubbled through an aqueous
solution of an aluminium(III) salt, a white precipitate of
aluminium(III) hydroxide is obtained.
(d) Hydrogen sulphide (formula weight 34) is a gas, water (formula
weight 18) is a liquid.
- Describe one laboratory method for the preparation of a dilute
solution of hydrogen peroxide.
In what way does a solution of hydrogen peroxide react with
(a) chlorine water, (b) potassium permanganate solution, (c) potas-
sium dichromate solution, (d) hydrogen sulphide? 50 cm^3 of an
aqueous solution of hydrogen peroxide were treated with an excess
of potassium iodide and dilute sulphuric acid; the liberated iodine
was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm^3
were required. Calculate the concentration of the hydrogen peroxide
solution in g I"^1.
(1MB, A)
