State your observations when: or
State one relevant observation for each of the
following reactions:
1. Iodine crystals are heated in a test tube. Refer to
practical chemistry notes.
2. A small piece of zinc is added to dilute
hydrochloric acid.
Brisk
effervescence / A colourless, odourless gas is given out which extinguishes a burning
splinter and itself burns with pop sound.
3. Iron nails are added to copper sulphate solution.
The
blue solution turns into a light green solution. A reddish brown deposit is observed.
4. Lead nitrate crystals are heated strongly.
A decrepitating sound is heard / A reddish brown gas is evolved. /
A residue which is yellow when hot and cold is left behind.
5. Ferric chloride crystals are exposed to atmosphere
for some time.
FeCl3
absorbs moisture from atmosphere and turns into a yellow solution.
6. Blue copper sulphate crystals are heated. Refer to
practical chemistry notes
7. Sulphur dioxide is passed through acidified
potassium dichromate solution.
Orange
potassium dichromate solution turns into a green solution.
8. Hydrogen
sulphide gas is passed through lead acetate solution.
A black precipitate of lead sulphide is
obtained.
9. A
piece of sodium is dropped in cold water.
10. Dilute Hydrochloric acid is added to Copper
carbonate.
A colourless and
odourless gas evolves with brisk effervescence which turns lime water milky.
11. A
piece of moist blue litmus paper is placed in a gas jar of chlorine.
The blue litmus paper turns red and then
it turns white.
12. Washing
Soda Crystals are exposed to the atmosphere.
Washing soda
crystals when exposed to atmosphere lose their water of crystallisation partially and crumble to form a
powder.
13. HCl
gas is passed through AgNO3 solution.
A curdy white precipitate is formed which is insoluble in mineral
acids but soluble in ammonium hydroxide.
14. Carbon
dioxide gas is passed through lime water.
Lime water turns milky.
15. NaOH
is added dropwise till in excess to ferrous chloride solution.
A dirty green precipitate is observed.
16. Barium
chloride solution is added to dilute sulphuric acid.
A
white precipitate is formed which is insoluble in all the mineral acids.
17. When ammonium dichromate is heated. Refer to practical chemistry notes
18. When crystals of copper nitrate are heated in
a test tube.
Reddish brown gas of
nitrogen dioxide gas is evolved and black residue of CuO is formed
19. Anhydrous calcium chloride is exposed to air for
some time.
Solid CaCl2 turns
into a colourless solution.
20. Action of dilute Hydrochloric
acid on iron (II) sulphide.
A colourless gas with a
rotten egg smell is evolved which turns moist lead acetate paper silvery black.
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