Procedure - To carry out the following Reactions and Classify them as Physical or Chemical changes. | Science Class 9 PDF Download

Burning of Magnesium in Air

Materials Required:

Lab Procedure: 

Inferences:

• Magnesium is a silvery white metal that burns in air and utilizes atmospheric oxygen from air to form magnesium oxide.

• Magnesium oxide changes the colour of red litmus paper to blue. This reaction shows that magnesium oxide is basic in nature.
• The formation of magnesium oxide is a direct combination reaction of two elements: magnesium and oxygen. Magnesium oxide is entirely different from the reactants magnesium and oxygen. So, this reaction is a chemical change.

Precautions:

1. The surface of magnesium ribbon should be properly cleaned with sand paper.
2. The white ash of magnesium oxide should not be touched.
3. Magnesium ribbon should be held by a pair of tongs while burning it.
4. It is better to use sun glasses to protect eyes from dazzling light of burning magnesium ribbon.

Reaction of Iron Nails with Copper Sulphate Solution in Water

Materials Required:

Lab Procedure:

• Clean two iron nails of sufficient size by rubbing with sand paper so that their colour appears greyish.
• Take sufficient quantity of copper sulphate solution in two test tubes and fix one test tube in each stand.
• Tie one iron nail with a thread and hang it in one test tube so that it is completely immersed in copper sulphate solution. Tie the other end of the thread with the stand.
• Keep the other nail in a petri dish for comparison after the experiment.
• Keep the two test tubes undisturbed for about 15 min.
• After 15 min. remove the iron nail immersed in copper sulphate solution and put it in the petri dish.

Observations:

• There is a brown coating on the iron nail which was dipped in the copper sulphate solution, whereas the iron nail placed in petri dish shows greyish colour of iron.
• The colour of the copper sulphate solution in which the iron nail was dipped turns light greenish, whereas the solution of copper sulphate in the other test tube does not change.

Inferences:

• The brown coating on the iron nail shows that copper is deposited on the iron nail by displacing iron.
• The greenish colour of the solution in the test tube shows that Fe²⁺ ions are present in the solution.
• This shows that iron is more reactive than copper as Fe²⁺ ions have displaced Cu²⁺ ions from copper sulphate solution and form light greenish coloured ferrous sulphate solution.

• This is a single displacement reaction in which copper has been displaced by iron from copper sulphate solution and a new compound, ferrous sulphate, is formed. So, this reaction is a chemical change. 

Precautions:

1. Clean the iron nails by rubbing them with sand paper to remove rust, dust or greasy surface.
2. Keep the control experiment to compare the colour of iron nails and copper sulphate solution.
3. Avoid touching copper sulphate solution or a nail dipped in copper sulphate solution. As copper sulphate is poisonous.

Heating of Copper Sulphate

Materials Required:

Lab Procedure:

• Take a small amount of copper sulphate crystals in a dry boiling tube.
• Hold the boiling tube with a test tube holder.
• Heat the boiling tube over the flame of a burner first gently and then strongly.
• Observe the colour of copper sulphate crystals after heating for some time.
• Note the water droplets along the sides of the boiling tube.
• Remove the boiling tube from the flame and cool.
• Add 2-3 drops of water on the sample of copper sulphate obtained after heating.

Observations:

• On heating, the colour of copper sulphate crystals changes from blue to white.
• There are water droplets on the walls of the boiling tube.
• On adding 2-3 drops of water white copper sulphate turns blue.

Inferences:

• Copper sulphate crystals contain water of crystallisation (CuSO₄.5H₂O).
• On heating, hydrated copper sulphate loses its water molecule and forms white coloured anhydrous copper sulphate. 
• On adding water anhydrous copper sulphate changes to hydrated copper sulphate.
• It is a reversible chemical change.

Precautions:

1. Keep the mouth of the test tube away from your face and also from other classmates.
2. Always use test tube holder while heating the test tube.
3. Take a small quantity of copper sulphate crystals.

Reaction of Zinc with Dilute Sulphuric Acid

Materials Required:

Lab Procedure:

• Take a small quantity of dil. H₂SO₄ in a conical flask.
• Add a small quantity of zinc granules  to it.
• Bring a wet blue and red litmus paper near the mouth of the conical flask one by one.
• Cork the flask with a one bored cork and insert a jet tube through the hole in the cork.
• Bring a burning candle near the mouth of the fine jet tube.
• Pour a small amount of the solution from the conical flask into a test tube.
• Add few drops of sodium hydroxide solution into it. A white gelatinous precipitate is formed.
• Add excess of NaOH into the gelatinous precipitate.
• The precipitate is soluble in excess of NaOH.
• Take a small amount of the solution in another test tube and pass H₂S gas through it using Kipp's apparatus.
• A white precipitate is formed.

Observations:

• After adding zinc granules to dil. H₂SO₄ evolution of gas bubbles occurs.
• The gas coming out does not change the colour of blue and red litmus papers.
• On bringing the flame, the gas coming out of the jet tube burns instantaneously with a small explosion and produce a pop sound and the flame dips out.
• On adding NaOH to the small amount of solution taken from the conical flask, white gelatinous precipitate is formed which is soluble in excess of NaOH.
• On passing hydrogen sulphide gas through the solution taken in the test tube a white precipitate is formed.

Inferences:

• Zinc reacts with dil.H₂SO₄ to form zinc sulphate and evolve hydrogen gas.

• The test with red and blue litmus papers shows that hydrogen gas is neither acidic nor basic in nature.
• NaOH reacts with ZnSO₄ to form a white gelatinous precipitate of zinc hydroxide (Zn(OH)₂) which is soluble in excess of NaOH.

• ZnSO₄ reacts with H₂S to form a white precipitate of zinc sulphide (ZnS).

• Zinc metal is more reactive than hydrogen.
• This is a single displacement reaction of a non-metal by a metal. 
• ZnSO₄ is entirely different in chemical composition and chemical properties than Zn and H₂SO₄. So it is a chemical change

Precautions:

1. Use the chemicals judiciously.
2. Do not inhale gases evolved directly.
3. Hydrogen gas instantaneously burns with mild explosion. Therefore, a fine jet tube should be used to see the burning of hydrogen.
4. Handle acids and alkalies carefully.

Reaction between Sodium Sulphate and Barium Chloride

Materials Required:

Lab Procedure:

• Take a small amount of barium chloride solution in a test tube and pour it into a conical flask.
• Then take a small amount of sodium sulphate solution in another test tube and add it into barium chloride solution taken in the conical flask.
• Stir the contents of the conical flask and keep it undisturbed for some time.
• After some time decant the upper solution from the conical flask and add a small amount of dil. HCl to the precipitate in the conical flask.

Observation:

• On adding sodium sulphate to barium chloride a white precipitate is immediately formed which is insoluble in dil.HCl.
• Sodium sulphate chemically reacts with barium chloride in the form of their aqueous solution to form a white precipitate of barium sulphate.           
• This reaction is a chemical change, as the products are entirely different from the reactants in chemical composition and chemical properties.