Question

State one relevant observation for each of the following reactions:
(i) Flame test is performed with calcium nitrate.
(ii) Water is added to anhydrous copper sulphate.
(iii) Copper carbonate is decomposed on heating.
(iv) Dil. H2SO4 is added to zinc sulphide.
(V) Addition of silver nitrate solution to sodium chloride solution.​

Answer 1

Explanation:

i) Brick red flame

ii) White amorphous powder changes to blue crystals

iii) Colourless gas evolved which turns lime water milky but has no effect on acidified K2Cr2O7 soln

iv) Rotten egg smelling gas which turns moist lead acetate paper silvery black

v) Curdy white ppt. obtained

Answer 2

Copper sulphate turns Blue

Explanation:

(i) The flame is orange-red.

• Observing visually, Calcium nitrate produces flame which is of orange-red.
• The colour of flames depends on the element's differing in the characteristic emission spectrum.

(i) Copper sulphate turns blue.

• Observing visually, after the reaction colour of the white copper sulphate will turn blue.
• Observing chemically, the copper sulphate crystal would absorb the water molecules which performs d-d transition to emit blue colour.

(iii) Green colour changes to black colour.

• Observing visually, the green colour of copper sulphate changes to the black colour of copper oxide.
• Copper (II) carbonate(green colour) decomposes when heated forming copper oxide (black coloured) and carbon dioxide.

(iv) A colourless solution of zinc sulphate.

• Observing visually, a colourless solution is formed which is of zinc sulphate.
• Observing chemically, zinc will react with sulphuric acid forming zinc sulphate in a solution phase releasing hydrogen gas.

(v) A white precipitate.

• Observing visually, a white precipitate is formed.
• Observing chemically, sodium nitrate and a white precipitate of silver chloride is formed.