EXPERIMENT
Aim
To performand observe the following reactions and classifiy(6)them mto:
Decomposition reaction
(a) Combination reaction reaction.
(d) Double displacement
(c) Displacement reaction
1. Action of water on quick lime.
2. Action of heat on ferrous sulphate crystals.
3. Iron nails kept in copper sulphate solution.
4. Reaction between sodium sulphate and barium chloride solutions.
Theory
Action of water on quicklime
Ca(OH), also called as
>Quicklime is calcium oxide (CaO), t combines with water to form calcium hydroxide,
slaked lime.
CaO(s)+ H,0) Ca(OH), (aq) + Heat
Quicklime Water Slaked lime
lwo substances are combining to form one product, therefore it is a combination reaction.
> Heat is released in the reaction, therefore it is an exothermic reaction.
> Slaked lime solution turns red litmus blue, therefore it is basic in nature.
> The freshly prepared slaked lime is alsocalled as lime water.
> It turns milky when carbon dioxide gas is passed through it.
Action of heat on ferrous sulphate crystals
}Ferrous sulphate crystals are light green in colour. The colour is due to the presence of water of crystallisation.
> On heating the crystals of ferrous sulphate, it undergoes the following changes:
2FeSO,7H,0(s)
Ferrous sulphate
Fe,O, (s) + S0,(g) +Sulphur
Ferric oxide
So,(g)
Sulphur dioxide
trioxide
+ 14H,0() Water
(Light green) (Brown) (Colourless) (Colourless)
> The colour changes to brown due to the formation of Fe,0,; SO, and SO, gases are
released.
Water of crystallisation is released by the crystals.
> Single compound decomposes to form three new compounds, therefore it is a
> SO, and SO, gases turns moist blue litmus paper into red, therefore it is acidic
decomposition reaction.
in nature.
> SO shows reducing property: t changes the orange colour of
acidified potassium dichromate to green when it
is allowed to pass through the acidified potassium dichromate solution.
> SO gas has a choking smell, do not inhale the
gas, keep the mouth of the test tube away from vour
> so: In the presence of water, face.
sulphur dioxide Is able to decolourise substances. Specifically, it is used
naners and delicate materials such as clothes. Oxygen for bleaching
in the atmosphere reoxidises the reduced dyes.,
so-Sulphur trioxide causes serious burns on bon innalaton and ingestion, estoring the colou.
since it is highly
violently and produces highly comosive nature. SO,
should be handled with extreme care as reacts with water in
Iron nails kept in copper sulphate solution corrosive sulphuric aCId.
Fe(s) + CuSO,(aq) ’ FeSO, (aq) + Cu(s)
Iron Copper sulphate Ferrous sulphate Copper
(Grey) (Blue) (Light green) (Reddish brown)
Ts noils when kept in blue
coloured solution o Copper sulphate it shows
(a) The blue colour solution changes slowly into light green colour. following changes:
aions replace Cuz* ions and form ron Suipnale in ne
(c) Iron nail gets the deposit of reddish brown copper metalsolution,
on it.
therefore it is called a displacement reaction.
(d) Fe atom forms Fe* jons by loss of
Cu atom and undergoes reduction.
electrons and undergoes oxidation and Cu ions by gain of electrons become
40
10
Reaction between sodium sulphate and barium chloride solutions
Na,SO,(aq) + BaCl, (aq) + BaSO,(s) + 2NaCl(aq)
Sodium sulphate Barium chloride Barium sulphate Sodium chloride
(White ppt.)
> Sodium sulphate solution and barium chloride solution are colourless.
> Mixing of both the solutions gives white coloured precipitate due to the formation of barium sulphate.
>The exchange of metal ions takes place in the reaction and is called a double displacement rcaction.
> Barium sulphate is insoluble in water and forms aprecipitate.
Materials Required
Abeaker, four test tubes, test tube holder, tongs, test tube stand, a dropper, a piece of sand paper and bunsen burner.
Chemicals required: Asmall piece of qicklime, ferrous sulphate crystals, iron nails (clean and unrusted), copper sulphate
solution, aqueous sodium sulphate solution, barium chloride solution, distilled water and dil. sulphuric acid solution.
Procedure
Experiment Observation Inference
1. Combination Reaction: Take a clean Reaction occurs with erackling An exothermic and combination
beaker, keep a small piece of limein it and sound and steamy vapours are reaction 0Ccurs.
add water drop by drop into the beaker. released. The beaker becomes hot.
Equation: CaO(s) + H,00)
Calcium oxide
+Ca(OH), (aq) + Heat
Water Calcium bydroxide
(Quicklime) (Slaked lime)
2. Decomposition Reaction: Take a clean The green crystals become reddish- Iron sulphate (green) crystals
and dry test tube, add few crystals of brown, tiny droplets of water are decomposes due to heat. Water
ferrous sulphate. Fix it on a test tube settled near the neck of thetest tube of crystallisation is collected in
holder. Heat the test tube on burner, and a colourless gas with choking the test tube.Turning potassium
keeping the mouth of test tube away smell is evolved. dichromate paper green shows
from your face. Waft the gas released The acidified potassium dichromate SO, gas. It is a decomposition
to smell and test it with acidified paper changes its colour from orange eacuon.
potassium dichromate paper. to green when held in the gas.
Equation: 2FeSO,-7H,0(s)
Ferrous sulphate
+Fe,O, (s) + SO,(g) + SO,(g) + 14H,0()
Ferric oxide Sulphur dioxide Sulphur trioxide Water
(Light green) (Brown) (Colourless) (Colourless)
K,Cr,0,(aq) + H,S0,(aq) +3S0,(g) Cr,Chromium
(S0,), (aq) + K,S0, (aq) + H,O)
sulphate
3. Displacement Reaction: Take a clean The blue colour of copper sulphate | Iron metal is more reactive
test tube, add 2-3 mL of copper sulphate slowly fades away. The iron nail than copper, so displaces it to
solution in it. Place an iron nail cleaned gets the deposit of reddish brown form iron sulphate soluion. It
with sand paper in it. Keep it on the test colour. is a displacement reaction and
tube stand and observe the changes for|The blue colour of solution changes reddish-brown deposit of copper
about 30 minutes. to green. is tormed on the ron nail.
Equation: CuSO,(aq) + Fe(s) + FeSO,(ag) + Cu(s)
(Blue) (Grey) (Light green) (Reddish brown)
4. Double Displacement Reaction: In a clean Both sodium sulphate and barium The white insoluble precipitate
test tube, take sodium sulphate solution, chloride solutions are colourless. of bariumsulphate is formed.
to this add barium chloride solution.On mixing together a whitet is a double displacement
Shake the contents and observe. precipitate is formed. reaction.
|Equation: Na,SO,(aq) + BaCI,(aq) +BaSO,(s) +2NaClaq)
(Colourless)
(Colourless) Barium sulphate
Sodium chloride
(White ppt.)
RACTICAL SKLLS IN SCIENCE-10 41
APrecautions
1. Do not touch quicklime with hands, use tongs.
add water drop by drop and use hor.
Z. MIXing of quicklime and water releases large amount of heat, so
beaker.
3. For heating, use hard glass tubes.
4. Never inhale any gas, just waft the gas.
5. Do not touch any chemical with bare hands.
your face while heating.
6. Keep the mouth of the test tube away from copper sulphate solution.
must be cleaned properly by using sand paper before dipping them in
7. The iron nails
