Performing and observing the reactions and classifying them:


Aim

To perform and observe the following reactions and classify them into:

i. Combination reaction
ii. Decomposition reaction
iii. Displacement reaction
iv. Double displacement reaction

A. Action of water on quicklime
B. Action of heat on ferrous sulphate crystals
C. Iron nails kept in copper sulphate solution
D. Reaction between sodium sulphate and barium chloride solutions.


Experiment A


Aim

To perform and observe the action of water on quicklime and also to identify the type of reaction involved.

Apparatus and Chemicals

  • 250 mL beaker
  • China dish
  • Asbestos sheet
  • Dropper
  • Quick lime
  • Water

Principle

Quicklime is calcium oxide, CaO. It reacts with water to give calcium hydroxide, Ca(OH)2. The reaction is exothermic in nature.
CaO + H2O Ca(OH)2

This is an example of combination reaction, in which two reactants i.e., calcium oxide and water, react to give one product i.e., calcium hydroxide.

Procedure

  • Take some (5-10 g) of quicklime in a clean and dry china dish. You need not powered it, even it is lumply.
  • Place the china dish on an asbestos sheet.
  • Take some water in a beaker. With the help of a dropper sprinkle some droops (4-5 drops) of water on a quick lime in the china dish.
  • Carefully record your observations in the note book.

Observations

S.No. Experiment Observation
1. Note the evolution or absorption of heat — if any, during the reaction by touching the china dish before
and after the experiment.
The china dish becomes hot after the reaction. indicating that the reaction is exothermic in nature.
2.Note the evolution of any gas or vapour during the reaction. A part of the water added is converted into steam by the heat of the reaction.
3.Note the sound produced — if any, during the reactionA hissing sound is produced during the reaction.
4. Note the physical changes produced — if any, in the reactants
during the reaction
The lumply quick-lime crumbles to give a fine powder. A part of the water added turns into steam due to the heat produced during the reaction.

Inference : The reaction between quicklime (calcium oxide) and water is an exothermic reaction. In this reaction calcium oxide and water reacts to give calcium hydroxide. The reaction is accompanied by a hissing sound. This is an example of combination reaction.

Precautions

  • China dish should be clean and dry before before the experiment.
  • Do not add too much water.
  • Sprinkle water carefully over the quick lime and protect yourself from the hot steam formed during the reaction.
  • Touch the hot china dish carefully after the experiment.

Experiment B

Aim

To perform and observe the action of heat on ferrous sulphate crystals and also to identify the type of reaction involved.

Apparatus and Chemical

  • Hard glass test tubes
  • Test tube holder
  • Test tube stand
  • Asbestos sheet
  • Bunsen burner
  • Fresh ferrous sulphate crystals (light green coloured)

Principle

Chemical composition of ferrous sulphate crystals is FeSO4. 7H2O i.e., ferrous sulphate exist as its heptahydrate in crystalline form. It is also known as green vitrol. When strongly heated it decompose into ferric oxide, steam, sulphur dioxide and sulphur trioxide.
2( FeSO4.7H2O) Fe2O3 + SO2 ↑ + SO3 ↑ + 14 H2O ↑

It is an example of decomposition reaction.

Procedure

  • In a clean and dry test tube, take a nearly 10 g of fresh light green coloured powered crystals of ferrous sulphate.
  • Heat the test tube over a burner by using a test tube holder.
  • Note the colour and smell of gases of vapours evolved.
  • continue heating till the colour of the residue in the test tube changes.
  • Place the hot test tube on an asbestos sheet to cool down.
  • Note the colour of the residue when it has cooled down.
  • Record your observation in the notebook.

Observations and Inference

S.No.ObservationExperiment Inference
1.Note the colour of from ferrous sulphate crystals.pale green Ferrous sulphate crystals are light green in colour.
2. Note the colour and smell of gas/ vapour evolved on heating ferrous sulphate crystals.Pungent smelling colourless gas with a smell of burning sulphur. Sulphur dioxide is a colourless gas with a smell of burning sulphur.
3. Note the colour of the residue after cooling It is red in colour. Iron (III) oxide is red in colour.

Light green coloured crystals of ferrous sulphate on heating decomposes to give a mixture of gasses (SO2 and SO3) and a red coloured residue (Fe2O3). It is an example of decomposition reaction.

Precautions

  • Test tube used for the experiment should be clean and dry.
  • Carry out the experiment in an open and well ventilated place or in fume cupboard.
  • Continue heating the test tube strongly till a red coloured residue is obtained.
  • Use only fresh light green coloured crystals of ferrous sulphate for the experiment.
  • Use only hard glass or borosil test tube for the experiment.

Experiment C

Aim

To perform and observe the action of copper sulphate solution on iron nails and also to identify the type of reaction involved.

Apparatus and Chemical

  • 250 mL beakers (2 Nos.)
  • Sand paper
  • Filter paper
  • Iron nails (new)
  • Copper sulphate solution

Principle

Iron is more reactive than copper. As such iron will displace copper from copper sulphate solution. Thus when iron (say in the form of nails) is kept in copper sulphate solution, iron displaces copper from copper sulphate and iron nails are covered with a thin reddish brown layer of copper. The reaction involved in the process is as follows.

Fe + CuSO4 FeSO4 + Cu

CuSO4 is sky blue in colour and FeSO4 is pale green in colour. As such the colour of the solution changes from sky blue to pale green after the reaction. This is an example of displacement reaction.

Procedure

  • Take nearly 100 mL of copper sulphate solutiion in 250 mL beaker. Note the colour of the solution
  • Take 2-3 iron nails (nearly 3 cm long). The iron nails should be new and free from rust. Clean these nails with a sand paper and wash with water. Note the colour of the iron nails.
  • Place these iron nails in the copper sulphate solution and observe the change in colour of copper sulphate solution as well as of iron nails.
  • After nearly 15 minutes remove the remove the iron nails from the solution. wash with water and place it on filter paper to dry.
  • Note the colour of the solution as well as of iron nails after the reaction.

Observations and Inference

S.No. Experiment Observation Inference
1. Note the colour of the copper sulphate solution before the experiment It is sky blue in colour Copper sulphate solution is sky blue in colour.
2. Note the colour of the iron nails before the experiment.steel grey Iron nails are steel grey in colour.
3.Note the colour of the nails after the experiment. Reddish brown Reddish brown colour of the nails is due for the deposition of copper on iron.
4. Note the colour of the pale green solution after the experiment.Pale green Ferrous sulphate solution is pale green in colour.

Iron nails, which are steel grey in colour, when place in sky blue coloured copper sulphate solution displaces copper from copper sulphate solution. In this process the iron nails are covered with a thin layer of reddish brown coloured copper while the colour of the solution changes from sky blue to light pale green coloured. It is an example of displacement reation.

Precautions

  • Iron nails should preferably new.
  • Clean the iron nails with a sand paper till the surface of iron nails acquires a shining appearance.
  • Iron nails should completely dip in copper sulphate solution.
  • Wait for the reaction to complete. It may take more time in winter than in summer. After the reaction solution should be light green in colour.
  • Don’t rub the iron nails covered with copper after the experiment.

Experiment D

Aim

To perform and observe the reaction between sodium sulphate and barium chloride solutions and also identify the type of reaction involved.

Apparatus and Chemical

  • Beakers (250 mL)
  • Test tubes
  • Test tube stand
  • Glass rod
  • Barium chloride solution
  • Sodium sulphate solution
  • Distilled water

Principle

Both barium chloride and sodium sulphate dissolve freely in water to give colourless solution (use only distilled water). On mixing the two solution as curdy white precipitate of barium sulphate is obtained. This is because barium sulphate in insoluble in water and is white in colour.
BaCl2 + Na2SO4 BaSO4 + 2NaCl

It is an example of double displacement reaction. This is because in this reaction one component each of both the reacting molecules get exchanged to form the products.

Procedure

  • In a clean beaker take nearly 290 mL of sodium sulphate solution and lebel it. Note its colour and appearance.
  • In a clean and dry test tube take nearly 10-15 mL of barium chloride solution and lebel it. Note its colour and appearance. Put it in the stand.
  • Add barium chloride solution sulphate solution with constant stirring and observe the changes produced.
  • Record your observations in the notebook.

Observations and Inference

S.No.Experiment ObservationInference
1. Note the colour and appearance of barium chloride solution.It is transparent and colourless. Barium chloride is colourless and freely soluble in water.
2.Note the colour and appearance of sodium sulphate solution. It is transparent and colourless. Sodium sulphate is colourless and freely soluble in water.
3. Note the colour and appearance of the reaction mixture after mixing of the two solution.(a) The precipitates formed are white in colour.

(b) The precipitates formed are white in colour.
A solution of sodium chloride in water is colourless. It is freely soluble in water.

Barium sulphate is white in colour. It is insoluble in water.

Both Barium chloride and sodium sulphate solutions are clear and colourless. On adding barium chloride solution to sodium sulphate solution, a curdy white precipitates is formed. It is due to the formation of insoluble barium sulphate. It is an example of double displacement reaction.

Precautions

  • Use only clean and dry test tube for the barium chloride solution.
  • Use only distilled water to wash the test tubes.

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