INTRODUCTION
In this experiment, we will perform some reactions and classify them as chemical and physical changes. Let us study the types of reactions and changes.
AIM
To perform the following reactions and classify them on the basis of chemical and physical changes.
1. Burning of magnesium in air,
2. Heating of copper sulphate,
3. Iron with copper sulphate solution in water,
4. Solution of sodium chloride and barium sulphate in water.
5. Zinc with dilute sulphuric acid.
1. REACTION BETWEEN IRON AND COPPER SULPHATE SOLUTION IN WATER
APPARATUS REQUIRED
1. CuSO4 solution,
2. Iron nails,
3. Test tube,
4. Clamp stand,
5. Thread.
6. Sandpaper.
THEORY
1. The colour of pure iron is greyish.
2. The aqueous solution of ferrous sulphate is pale green due to the presence of Fe²+ ions.
3. The colour of pure copper is reddish-brown.
4. The aqueous solution of copper sulphate is blue due to the presence of Cu²+ ions.
5. Iron is more reactive than copper; therefore it displaces copper from its salt solution.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s).
Black Blue Pale green reddish
PROCEDURE
1. Make iron nail greyish by rubbing it with sandpaper.
2. Take copper solution in two test tubes. Label these test tubes as A and B and fix them on two separate clamp stands.
3. Tie one end of the thread with an iron nail and immerse it in solution B. Tie the other end of the thread with the clamp stand as shown in the figure.
A B
4. Put the other iron nail on a white sheet.
5. Keep the solution undisturbed for some time.
6. Now, remove the iron nail from solution B and put it along the other side of the iron nail on a white sheet.
7. Record your observations.
OBSERVATION
| S.NO | OBSERVATIONS | INFERENCE |
|---|---|---|
| 1. | The colour of solution B has turned pale. | Iron displaced copper from copper sulphate solution. |
| 2. | The reddish-brown coating can be seen on the iron nail. | Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s). |
RESULT
Iron has displaced copper from its salt solution in this reaction because iron is more reactive than copper. Therefore this reaction will be a displacement reaction.
PRECAUTION
1. Iron nails should be cleaned thoroughly with sandpaper before reaction.
2. Wash your hands properly after experimenting.
3. Don’t touch the iron nail coated with copper.
4. Don’t touch the test tube during the reaction.
5. Keep your eyes away from the reaction.
6. Maintain a distance while doing any reaction.
2. BURNING OF MAGNESIUM IN AIR
APPARATUS REQUIRED
1. A burner,
2. Tongs,
3. Watch glass,
4. Red litmus paper,
5. Magnesium ribbon
THEORY
1. Magnesium is reacting with oxygen to form magnesium oxide.
2Mg + O2 →2MgO
2. This metal is very active.
3. In this reaction, 2 moles of magnesium are combined with 1 mole of oxygen to form 2 molecules of magnesium oxide. This type of reaction is known as a combination reaction.
4. The nature of magnesium oxide is basic, and when it dissolves in water, it forms magnesium hydroxide, which is also basic in nature.
MgO + H2O → Mg(OH)2
5. Red litmus turns blue by magnesium oxide.
PROCEDURE AND OBSERVATION
| S.NO | EXPERIMENT | OBSERVATION | INFERENCE |
|---|---|---|---|
| 1. | With the help of sandpaper, clean the magnesium ribbon and introduce it to the flame through tongs. | A white light comes out while burning magnesium, and a white powder of MgO is formed. | Magnesium burns in the presence of air and forms MgO on combining with oxygen. |
| 2. | Collect the white powder in a watch glass and add some water to it. Dip a red litmus in the solution. | Red litmus turned into blue. | The nature of MgO is basic. |
RESULT
When magnesium burns in the air, it gives out a white light and combines with oxygen, and it forms a magnesium oxide which is basic in nature.
PRECAUTIONS
1. Magnesium should be cleaned thoroughly with sandpaper before reaction.
2. Wash your hands properly after experimenting.
3. Don’t see directly the bright light of magnesium.
4. Don’t touch the test tube during the reaction.
5. Keep your eyes away from the reaction.
3. A REACTION BETWEEN ZINC AND DILUTE SULPHURIC ACID
APPARATUS REQUIRED
1. Dilute sulphuric acid,
2. Zinc granules,
3. Clamp stand,
4. Boiling tube,
5. Cork fixed on a capillary tube.
THEORY
Being above hydrogen in the reactivity series, zinc displaces hydrogen from dilute sulphuric acid.
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(s)
Reaction of sulphuric acid with zinc
PROCEDURE AND OBSERVATION
| S.NO | EXPERIMENT | OBSERVATION | INFERENCE |
|---|---|---|---|
| 1. | Put some H2SO4 in a boiling tube filled with zinc granules. Immediately close the tube with a cork. Bring a burning candle near the tube. | A brisk reaction occurs, and gas evolves. A pop burning sound comes out of gas evolved. | This is a displacement reaction as the zinc displaces hydrogen from the reaction. |
RESULT
The reaction between zinc and sulphuric acid gives out hydrogen and zinc sulphate.
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(s)
PRECAUTION
1. Be extra careful while performing the experiment.
2. Small jets should be used to test hydrogen gas.
4. HEATING OF COPPER SULPHATE
APPARATUS REQUIRED
1. Hydrated copper sulphate,
2. Test tube,
3. Blue litmus paper,
4. Burner,
5. Test tube holder.
THEORY
1. The chemical formula for copper sulphate pentahydrate is CuSO4.5H2O. Its colour is blue. On heating, it loses water molecules and turns to anhydrous copper sulphate of white colour.
CuSO4.5H2O(s) → CuSO4(s) + 5H2O
(Blue) (White)
2. The above reaction can be regained by adding 5 molecules of water to the copper sulphate solution.
CuSO4(s) + 5H2O → CuSO4.5H2O(s)
(Blue) (White)
3. On heating copper sulphate pentahydrate, we obtain the CuO (copper oxide), SO3 (sulphur trioxide) and 5H2O
CuSO4.5H2O(s) →CuO(s) + SO3(s) + 5H2O
4. Decomposition reaction is the process in which one substance breaks down to form two or more or more than two products while undergoing any reaction.
PROCEDURE AND OBSERVATION
| S.NO | Experiment | Observation | Inference |
|---|---|---|---|
| 1. | Take a small amount of copper sulphate in a test tube and heat it. | The blue colour of copper sulphate will be changed into dirty white. | Hydrated Copper sulphate loses water and converts into anhydrous copper sulphate. |
| 2. | Taking anhydrous copper sulphate in another test tube, add a few drops of water to it. And heat it. | The white colour of anhydrous copper sulphate turns into blue colour. A black residue is obtained, and pungent-smelling gas evolves. | The copper sulphate pentahydrate is regained. The black residue is copper oxide, and the gas is sulphur trioxide. |
| 3. | Bring a blue litmus paper near the test tube and observe. | Blue litmus turned to red. | Sulphur trioxide gas is acidic in nature. |
RESULT
On heating copper sulphate pentahydrate, it loses its water of crystallisation and turns into a dirty white colour. The anhydrous copper sulphate decomposes to copper oxide and sulphur trioxide on further heating.
PRECAUTIONS
1. Don’t touch or taste copper sulphate as it is poisonous.
2. Don’t bring sulphur trioxide into moisture as sulphur trioxide forms sulphuric acid after coming into contact with moisture.
3. Hydrated copper sulphate should be heated gently, and anhydrous copper sulphate should be heated firmly.
5. REACTION BETWEEN SODIUM SULPHATE AND BARIUM CHLORIDE IN THE FORM OF THEIR AQUEOUS SOLUTION
MATERIAL REQUIRED
1. Test tube,
2. Test tube holder,
3. Aqueous solution of sodium sulphate and barium chloride.
THEORY
Barium sulphate forms by mixing barium chloride and sodium sulphate solution. It forms as a white precipitate. This is represented by the following reaction.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq).
Barium sulphate forms as a white precipitate due to the reaction between ions SO4²- and Ba²+.
This type of reaction is called a double displacement reaction, in which an exchange of ions takes place.
PROCEDURE AND OBSERVATION
| S.NO | EXPERIMENT | OBSERVATION | INFERENCE |
|---|---|---|---|
| Take 5 ml each of barium chloride and sodium sulphate in two test tubes and mix them together in a separate tube. | A white precipitate of barium sulphate is formed. | Barium sulphate is formed due to the double displacement reaction. |
RESULT
The reaction between sodium sulphate and barium chloride form a white precipitate of barium sulphate. This type of reaction is called the double displacement reaction.
PRECAUTION
1. Chemicals should be used in small amounts.
2. Wash your hands thoroughly after performing experiments.
VIVA QUESTIONS WITH ANSWERS
Q.1 Which colour does the pure iron show?
ANS. Greyish
Q.2 What is the colour of an aqueous solution of ferrous sulphate, and why?
ANS. Pale green due to the presence of Fe²+ ion.
Q.3 Which metal colour is reddish-brown?
ANS. Pure copper.
Q.4 What do you understand about a chemical reaction?
ANS. Those reactions in which the bonds between different substance changes to form new substances with new properties.
Q.5 Heating of copper sulphate is what kind of reaction?
ANS. Displacement reaction
Q.6 What is the chemical formula, colour and odour of sulphur trioxide?
ANS. SO3, colourless and pungent-smelling gas.
Q.7 Which substance will form when bringing sulphur trioxide into moisture?
ANS. Sulphuric acid.
Q.8 What do you mean by displacement reaction?
ANS. Reactions in which more reactive metals displace a less reactive metal is known as displacement reaction.
Q.9 Why should we clean magnesium before heating?
ANS. To clean the deposited layer of oxide on the surface of magnesium.
Q.10 What is the use of litmus paper?
ANS. To find the acidic and the basic nature of any substance.
Saquib Siddiqui is a Mechanical Engineer and a content creator. He has special interest in science experiments and teaches the same to school and college students. He is also a technical lead at RUDE LABS PVT. LTD.
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