CBSE Class 9 Science Practical Skills – Types of Reactions and Changes
EXPERIMENT
AIM
To carry out the following reactions and classify them as physical or chemical changes.
- Iron with copper sulphate solution in water
- Burning of magnesium in air
- Zinc with dilute sulphuric acid
- Heating of copper sulphate
- Sodium sulphate with barium chloride in the form of their solutions in water.
(1) Reaction between Iron and Copper Sulphate solution in water
MATERIALS REQUIRED
Two iron nails, CuS04 solution, test tube, clamp stand, thread.
THEORY
Pure iron is greyish in colour. Pure copper is reddish brown in colour. Due to the presence of Cu2+ ions, aqueous C solution of copper sulphate is blue. Due to the presence of Fe2+ ions, aqueous solution of ferrous sulphate is pale green. Iron being more reactive than copper displaces copper from its salt solution.
PROCEDURE
- Clean an iron nail by rubbing with sand paper so that it appears greyish.
- Take two test tubes and labelled them as A and B. In both test tubes, add 10 ml of freshly prepared copper sulphate solution and fix these test tubes in two separate clamp stands (Fig 4.1).
- Tie a thread to the nail and hang it in test tube B. Care should be taken so that the iron nail is completely immersed in CuS04 solution. Tie other end of thread to stand as shown in Fig 4.1.
- Keep the other iron nail on a white sheet of paper.
- Leave the set-up undisturbed for sometime.
- Remove the nail from the solution and keep it along the side of second iron nail on sheet of paper. Record your observations.
OBSERVATION AND INFERENCE
RESULT
The reaction between Fe and CuS04 shows that Fe is more reactive than Cu and the reaction is a displacement reaction.
PRECAUTIONS
- Clean the iron nail properly by rubbing with sand paper.
- Copper sulphate solution is poisonous, so, handle it with care.
- During experiment, the test tubes should not be touched or disturbed.
- After completing experiment, iron nail coated with copper should not be touched.
(2) Burning of Magnesium in air
MATERIALS REQUIRED
Magnesium Ribbon, burner, tongs, watch glass, pH paper strip/red litmus paper.
THEORY
Magnesium is a very active metal. It reacts with oxygen to form magnesium oxide.
During this process two elements viz, magnesium and oxygen combine together to form a single compound magnesium oxide. Such type of reactions are called combination reactions.
Magnesium oxide is basic in nature because when this is dissolved in water it forms magnesium hydroxide which is basic in nature.
Magnesium oxide turns red litmus solution blue.
PROCEDURE, OBSERVATION AND INTERFENCE
RESULT
Mg burns in air giving out a flash of bright white light and combines with oxygen to form basic magnesium oxide. MgO is basic in nature
PRECAUTIONS
- Magnesium ribbon should be cleaned by rubbing with sand paper.
- Hold magnesium ribbon using tongs while burning it.
- Do not look at the bright light associated with burning Mg directly. Use sun glasses.
- White powder or magnesium oxide should not be touched.
(3) Reaction of Zn with dil. Sulphuric Acid
MATERIALS REQUIRED
Zinc granules, dil. H2S04 , clamp stand, boiling tube, cork fixed with a fine capillary tube.
THEORY
Zinc being more reactive or lying above hydrogen in the reactivity series, displaces hydrogen from dil. acids.
Zn(s) + H2S04 (aq) → ZnS04 (aq) +H2(g)
PROCEDURE,OBSERVATION AND INFERENCE
RESULT
Zinc reacts with sulphuric acid to produce hydrogen gas and zinc sulphate.
Zn(s) + H2S04 (aq) → ZnS04 (aq) +H2(g)
PRECAUTIONS
- Handle the chemicals with care.
- Use a small jet to test hydrogen gas, as hydrogen gas burns instantaneously with an explosion.
(4) Heating of Copper Sulphate
MATERIALS REQUIRED
Hydrated copper sulphate, test tube, test tube holder, burner, pH paper or blue litmus paper.
THEORY
Chemical formula of copper sulphate pentahydrate is CuS04.5H20 . It contains five moles of water per mole of copper sulphate. Because of water of hydration, the colour of copper sulphate pentahydrate is blue. When it is heated, it loses water molecules and turns to white coloured anhydrous copper sulphate.
The above process can be reversed. When water is added to anhydrous copper sulphate, its colour changes to blue. This shows that coloured hydrated copper sulphate has regained.
On further heating, anydrous copper sulphate decomposes to form sulphur trioxide gas and copper oxide.
The whole change of heating of copper sulphate pentahydrate can be given by the following equation:
The reaction in which a substance breaks down to form more than one products is called decomposition reaction.
PROCEDURE,OBSERVATION AND INFERENCE
RESULT
The hydrated copper sulphate loses water of crystallisation on gentle heating and becomes dirty white. On further heating strongly, it decomposes to black copper oxide and pungent smelling sulphur trioxide.
PRECAUTIONS
- Copper sulphate is a poisonous substance. Do not touch or taste it.
- Sulphur trioxide coming in contact with atmospheric moisture forms sulphuric acid. So, contact with sulphur trioxide must be avoided.
- In the beginning of experiment, copper sulphate should be heated gently. But after the formation of anhydrous copper sulphate test tube should be heated strongly.
(5) Reaction between Sodium Sulphate and Barium Chloride in the form of their Aqueous Solutions
MATERIALS REQUIRED
Test tube, test tube holders, aqueous solution of sodium sulphate and barium chloride.
THEORY
On mixing the solutions of sodium sulphate and barium chloride, a white precipitate of barium sulphate is formed which in insoluble in water. This chemical change can be represented by the following chemical equation:
In this reaction, white precipitate of BaS04 is formed by the reaction ofS042-and Ba2+. The other product formed is sodium chloride which remains in the solution. Such reactions in which there is an exchange of ions between the reactants are called double displacement reactions.
PROCEDURE, OBSERVATION AND INFERENCE
RESULT
The reaction between Na2S04 (aq) and BaCl2 (aq) yields an insoluble white precipitate of BaS04, indicating that the reaction is a double displacement reaction.
PRECAUTIONS
- Use the chemicals in small amounts.
- Wash your hands with soap after completing the experiment.
INTERACTIVE SESSION
Examiner :
What do you understand by a chemical reaction?
Examinee:
It is a chemical change in which bonds between reactants are broken and new bonds are made leading to new substances being formed with new properties.
Examiner :
Is it possible that only a reduction or oxidation reaction occurs?
Examinee:
No, reduction and oxidation reactions always occur together.
Examiner :
Why do displacement reactions occur?
Examinee:
Displacement reactions occur due to the difference in reactivities of metals.
Examiner :
What happens in a displacement reaction?
Examinee:
A more reactive metal displaces a less reactive metal from its salt solution.
Examiner :
Why do metals have different reactivities?
Examinee:
Metals have different reactivities because their electron donating tendency is different and all metals react by donating electrons.
Examiner :
Why is hydrogen displaced from the acid solution on reaction of zinc with dil. H2S04?
Examinee:
Hydrogen is displaced because Zinc is more reactive than hydrogen.
Examiner :
Give the colours of CuS04.5H20 and anhydrous CuS04.
Examinee:
Blue and dirty white respectively.
Examiner :
At what temperature, CuS04.5H20 loses four molecules of water?
Examinee:
100 °C
Examiner :
At what temperature, it loses five molecules of water?
Examinee:
250 °C
Examiner :
What is anhydride of H2S04? Give its colour and odour.
Examinee:
S03. It is colourless and pungent smelling gas.
Examiner :
Which acid is formed when S03 is dissolved in H20?
Examinee:
H2S04 is formed.
Examiner :
What type of reaction is heating of CuS04 strongly?
Examinee:
Decomposition reaction.
NCERT LAB MANUAL QUESTIONS
Question 1:
Why should magnesium ribbon be cleaned before burning it in air?
Answer:
Magnesium ribbon should be cleaned before burning to remove the oxide layer deposited over the magnesium ribbon which makes it passive, so that it can ignite easily.
Question 2:
Why does the red litmus paper turn blue when touched with aqueous solution of magnesium oxide?
Answer:
When magnesium oxide is dissolved in water, it forms magnesium hydroxide which is basic in nature. So aqueous solution of MgO turns red litmus paper blue.
Question 3:
Is there a possibility of a compound other than MgO formed in the reaction of magnesium with air?
Answer:
Yes, Mg also reacts with N2 present in air to form magnesium nitride (Mg3N2).
3Mg(s) +N2(g) → Mg3N2(s)
Question 4:
Why is it suggested to wear dark coloured goggles while watching the burning of magnesium ribbon in air?
Answer:
In order to prevent our eyes from the dazzling light produced.
Question 5:
Write the chemical reaction of zinc with dil. sulphuric acid.
Answer:
Question 6:
How does the combustion of hydrogen gas produce water?
Answer:
Question 7:
How will you show that the hydrogen gas is neutral in behaviour?
Answer:
Hydrogen gas neither turns red litmus paper blue nor it turns blue litmus paper red.
Question 8:
Fill in the blanks:
- Sodium sulphate and barium chloride are………. (ionic/covalent) compounds.
- As the white precipitate of barium sulphate is formed………… (immediately/sometime
after mixing the two solutions), the reaction between………….. (ionic/covalent)
compounds is………… (instantaneous/slow).
Answer:
- ionic
- immediately, ionic, instantaneous.
Question 9:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer:
The colour of copper sulphate solution changes from blue to pale green when an iron nail is dipped in it because Fe is more reactive than Cu and can displace it from its salt solution.
Question 10:
Answer:
The above reaction occurs because chlorine is more reactive than iodine and, therefore, displaces iodide ions from solution.
PRACTICAL BASED QUESTIONS
Multiple Choice Questions/VSA
Question 1:
Which one is true about the behaviour of MgO in the presence of water?
(a) It is basic.
(b) It is acidic.
(c) It is amphoteric,
(d) It is neutral.
Question 2:
When dilute hydrochloric acid is added to granulated zinc placed in a test tube, the observation made is
(a) the surface of the metal turns shining.
(b) the reaction mixture turns milky.
(c) greenish yellow gas is evolved.
(d) the colourless and odourless gas evolves with bubbles.
Question 3:
S03 is
(a) acidic
(b) basic
(c) neutral
(d) amphoteric.
Question 4:
2H2 + 02 →2H20 is an example of
(a) displacement reaction
(b) decomposition reaction
(c) combination reaction
(d) isomerisation reaction
Question 5:
When a process ‘X’ is applied to anhydrous copper sulphate, it turns blue. Here the process ‘X’ represents
(a) heating at 150°C
(b) heating at 110°C
(c) dissolution in water
(d) all of these
Question 6:
Question 7:
Combustion is an example of
(a) displacement reaction
(b) redox reaction
(c) decomposition reaction
(d) isomerisation reaction.
Question 8:
We will observe a precipitate to occur in the solutions when
(a) barium chloride is added to sodium sulphate.
(b) barium chloride is added to sodium chloride.
(c) sodium sulphate is added to sodium chloride.
(d) hydrochloric acid is added to barium chloride.
Question 9:
Barium sulphate is
(a) soluble in water.
(b) partially soluble in water.
(c) insoluble in water,
(d) a gas at room temperature.
Question 10:
Iron displaces copper from its salt solution because
(a) both Fe and Cu are equally reactive
(b) Fe is less reactive than Cu
(c) Fe is more reactive than Cu
(d) none of the above.
Question 11:
Sodium sulphate and barium chloride solutions are mixed in a test tube. The observation made is:
(a) greenish yellow gas is evolved
(b) a colourless gas is evolved
(c) a yellow precipitate is formed
(d) a white precipitate is formed.
Question 12:
Iron filings were added to a solution of copper sulphate. After 10 minutes, it was observed that the blue colour of the solution changes and a layer gets deposited on iron filings. The colour of (i) the solution and (ii) that of the coating on iron filings would respectively be
(a) (i) yellow and (ii) green.
(b) (i) brown and (ii) blue.
(c) (i) red and (ii) greenish blue.
(d) (i) green and (ii) reddish brown.
Question 13:
100 ml of a saturated copper sulphate solution was taken in a beaker. A small amount of iron filings was added to the beaker and left undisturbed overnight. The mixture was then filtered to obtain the residue. The colour of the residue was found to be
(a) greenish blue
(b) faint green
(c) steel grey
(d) reddish brown.
Question 14:
Which of the following is a double displacement reaction?
Question 15:
(a) This is a single displacement reaction
(b) The produced gas ‘X’ is acidic
(c) Zn is less reactive than hydrogen
(d) All of the above.
ANSWER KEY
Multiple Choice Questions/VSA
- (a)
- (d)
- (a)
- (c)
- (c)
- (a)
- (b)
- (a)
- (c)
- (c)
- (d)
- (d)
- (d)
- (b)
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