CBSE CLASS 10 Chapter 01: Chemical Reactions and Equations NCERT Activity explanation

X NCERT ACTIVITIES Class 10 Chemical Reactions and Equations

Activity 1.1 (Experiment):

Activity 1.1

Clean a magnesium ribbon by rubbing it with sandpaper to remove layer of carbonate and oxide.

Burn it using a spirit lamp you get white ash of  MgO.           

Mg (s) + O₂(g)    à MgO(s)

=> Magnesium ribbon burn with dazzling light and white powder of MgO is formed which is basic in nature

It is an example of combination reaction in which single compound break into two or more substance.

Activity 1.2 (Experiment):

Take lead nitrate solution in a test tube. Add potassium iodide solution to this.

=> Yellow precipitate PbI₂ is formed. Substance Insoluble in water is called precipitate.

Pb(NO₃)₂  (aq)     +      2KI    à PbI₂(s) (¯)    +  2 KNO₃  (aq)

This is an example of precipitation reaction . This is an example of Double decomposition reaction in which there is exchange of radicals.

Activity 1:3 (Experiment):

Take a few zinc granules in a conical flask or a test tube. Add dilute hydrochloric acid or sulphuric acid to this.

=> The bubble of hydrogen gas is observed. The temperature of flask increases due to release of heat energy.

Zn(s) + HCl(l)   --à ZnCl₂ (aq) + H₂ ( ­)

This is called Exothermic reaction as there is release of heat .

This is an example of Single displacement reaction in which more reactive element displace less reactive element from compound.

=> The following observations helps us to determine whether a chemical reaction has taken place 

􀂄 change in state                    

􀂄 change in colour

􀂄 evolution of a gas               

􀂄 change in temperature

To make a chemical equation more informative

The physical states of the reactants and products are mentioned along with their chemical formulae.

The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s), respectively.

The word aqueous (aq) is written if the reactant or product is present as a solution in water.

Sometimes the reaction conditions, such as temperature, pressure, catalyst, etc., for the reaction are indicated above and/or below the arrow in the equation. For example –

CO(g) + 2H₂ (g) ⎯340atm⎯→ CH₃OH(l) 

Zn + 2HCl → ZnCl2 + H2↑ + heat 

Zn + H2SO4 → ZnSO4 + H2↑ + heat

Activity 1.4 (Experiment):

Take a small amount of calcium oxide or quick lime in a beaker. And  slowly add water to this.

=> CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat         

(Beaker became hot due to release of heat)

It is an example of Exothermic or combination reaction.

Example of exothermic Reaction

2H₂(g) + O₂ (g) → 2H₂O(l) + heat

Burning of natural gas:  CH₄(g) + 2O₂ (g) → CO₂(g) + 2H₂O (g) + Heat

Decomposition of vegetable matter into compost and Respiration are also example of exothermic reaction.

Activity 1.5 (Experiment):

Take about 2 g ferrous sulphate crystals (Green in colour)in a dry boiling tube.

􀂄 Heat the boiling tube over the flame of a burner or spirit lamp .

􀂄 The green colour of the crystals after heating change to black ferric oxide and smell of burning sulphur as SO₂ and SO₃ is observed {rotten eggs (hydrogen sulfide)}

2FeSO₃(s) ⎯⎯Heat⎯→ Fe₂O₃(s) + SO₂ (g) + SO₃(g)

This is an example of thermal decomposition reaction as heat is envolved.

Ferrous sulphate crystals (FeSO₄, 7H₂O) lose water when heated and the colour of the crystals changes. This shows that ferrous sulphate crystals contain water molecules.

=> The water molecules present per mole of substance are known as crystallization of water.

=> When you add water into it to regain green colour.

Activity 1.6 (Experiment):

Heating of lead nitrate  We observe the emission of brown fumes of nitrogen dioxide (NO2). 

2Pb(NO3)2(s)    --Heat→   2PbO(s)   +  4NO2(g) +   O2(g)

Activity 1.7 (Experiment):

Aim: To show that water is a compound  containing two atoms of hydrogen and 1 atom
of oxygen

We will observe the bubbles of O₂ at Anode and H₂ at cathode.

􀂄 The volume of the gas collected in one test tube is double the other test tubes this is because one molecules of Water contains two parts of hydrogen and one part oxygen.

2H₂ + O₂  à 2H₂O

􀂄 Test these gases one by one by bringing a burning candle close to the mouth of the test tubes.

One gas H₂ catches fire and burn with pop sound and other gas O₂ matchstick burn brightly smoothly. 

Conclusion: Water is a compound containing two atoms of hydrogen and 1 atom of oxygen.

Activity 1.8 (Experiment):

Take about 2 g of white silver chloride in a china dish .Place this china dish in sunlight for some time

=> White silver chloride turns grey in sunlight due to the decomposition. This is called photodecomposition reactions. This is an example of Endothermic reaction.

2AgCl(s) ⎯⎯Sunlight →2Ag(s) + Cl₂(g)

Silver bromide also behaves in the same way.

2AgBr(s) ⎯⎯Sunlight →2Ag(s) + Br₂(g)

The above reactions are used in black and white photography

=> The decomposition reactions require energy either in the form of heat, light or electricity for breaking down the reactants.

Reactions in which energy is absorbed are known as endothermic reactions

Activity 1.9 (Experiment):

Take a iron nails and put them into test tube containing 10 mL copper sulphate solution.

=> The colour of iron nails dipped in the copper sulphate solution become brownish in colour and the blue colour of copper sulphate solution fade due to deposition of copper over iron nail.

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)         Single displacement reaction

Zn(s) + CuSO4(aq)→ ZnSO4(aq) + Cu(s)

Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s) 

Activity 1.10 (Experiment):

Aim: To show double displacement reaction 

Mix two solution a bout 3 mL of sodium sulphate solution and about 3 mL of barium chloride solution.

=> A white substance Barium sulphate which is insoluble in water called precipitate is formed.

Na₂SO₄(aq) + BaCl₂ (aq) → BaSO₄(s) + 2NaCl(aq)

A reaction in which there is an exchange of ions between the reactants are called double displacement reactions.

Activity 1.11 (Experiment):

Aim: To show oxidation and reduction reaction  

Heat a china dish containing about 1 g copper powder .

=> The surface of copper powder becomes coated with black copper(II) oxide due to oxidation of copper to

copper oxide. This is an example of oxidation reaction in which there is addition of oxygen or removal of hydrogen or loss of electron.

2Cu  ( Reddish brown) + O₂ ⎯⎯Heat →2CuO (black)

=> Now pass H₂ gas over the heated CuO the black coating turns to pink(reddish brown) again.

CuO +H₂ ⎯Heat⎯→ Cu+H₂O

CuO reduced to Cu and H₂ oxidised to H₂0

If a substance gains oxygen during a reaction, it is said to be oxidised. Here H₂

If a substance loses oxygen during a reaction, it is said to be reduced. Here CuO

When one reactant gets oxidised while the other gets reduced during a reaction. This reactions are called oxidation-reduction reactions or redox reactions.

ZnO + C → Zn + CO

Carbon is oxidised to CO and ZnO is reduced to Zn.

MnO₂ +  4HCl → MnCl₂ + 2H₂O + Cl₂

HCl is oxidised to Cl₂  by loosing hydrogen 

MnO₂ is reduced to MnCl₂ by loosing oxygen.

=>  if a substance gains oxygen or loses hydrogen during a reaction, it is oxidised.

If a substance loses oxygen or gains hydrogen during a reaction, it is reduced.

Activity 1.12

Take about 2 g barium hydroxide in a test tube. 

Add 1 g of ammonium chloride and mix with the help of a glass rod.

=> when we mix barium hydroxide with ammonium chloride the bottom of test tube became cold due to absorption of heat. so it is an endothermic reaction.

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