class 10 chemical reactions and equations important questions

Iron has displaced Copper from Copper sulphate and formed as Ferrous sulphate 

Ex 2:

Zn + CuSO₄                           ZnSO₄  +  Cu

(s)        (aq)                                 (aq)     (s)

Pb + Cl₂                                       PbCl₂ + Cu

(s)     (g)                            

Here Fe, Zn, Pb are more reactive element , they have displayed Copper less reactive element

Double Displacement Reaction / Metathesis

What is it?

It is a chemical reaction where two compounds react, and two ions or radicals interchange places and form new compounds.

Example 1:
Na₂SO₄ (aq) + BaCl₂ (aq) → BaSO₄ (s) + 2NaCl (aq)

• Sodium Sulphate + Barium Chloride → Barium Sulphate + Sodium Chloride
• SO₄²⁻ & Cl⁻ : Both interchange

Precipitate

It is an insoluble compound.
Any reaction that produces a precipitate is called a precipitation reaction.

BaSO₄ = White precipitate

Example 2:
Pb(NO₃)₂ (aq) + 2KI (aq) → PbI₂ (s) + 2KNO₃ (aq)

Lead Nitrate + Potassium Iodide → Lead Iodide + Potassium Nitrate

PbI₂ = Yellow precipitate

Oxidation & Reduction Reaction

• If a substance gains O₂ during reaction, it is said to be oxidized.
• If a substance loses O₂ during reaction, it is said to be reduced.

When one reactant get oxidised and other gets reduced. It is called as Oxidation reduction reaction or redox reaction

Ex:                     

CuO + H₂                             Cu + H₂O

CuO                               Cu 🡪 Reduction ( loses Oxygen)

Copper oxide                 Copper

H₂                           H₂O 🡪 Oxidation ( gains Oxygen)

Other Examples:

ZnO + C                            Zn + CO

Zinc    Carbon                  Zinc    Carbon  

Oxide                                           Monoxide

MnO₂ + 4HCl                           MnCl₂ + 2H₂O + Cl₂

MnO₂ – Manganese Oxide

HCl – Hydrochloric acid

MnCl₂  - Manganese Chloride

2H₂O - Water

Cl₂ – Chlorine 

Oxidised – Gains oxygen/ loses Hydrogen

Reduced – Loses oxygen/ gains Hydrogen 

Effect of oxidation in everyday life:

Corrosion :

The process in which metal is eaten up by air, moisture or chemical on their surface is called corrosion

Ex: Rusting of Iron

When Iron object is left in a place of high moisture for considerable amount of time it result in the formation of reddish brown substance

4Fe + 3O₂ + 6 H₂O 🡪 4Fe(OH)₃

Fe(OH)₃ – Hydrated Iron III Oxide (Rust)

• Corrosion causes damage to car bodies, bridges, iron railing, ships etc.
• It can be prevented by galvanisation (coating of Zn)
• Apply oil/grease/ paint 

Copper reacting with moisture:

2Cu + O₂ + H₂0 + CO₂ 🡪 Cu(OH)₂ + CuCO₃

Cu(OH)₂ + CuCO₃   🡪 Copper hydroxide and copper carbonate together forms the green coating on the object 

Silver kept in air get tarnished and turns black

2Ag + H₂S 🡪 Ag₂S + H₂

(s)         (g)       (s)      (g)

Ag – Silver

H₂S – Hydrogen Sulphide

Ag₂S – Silver sulphide 

Rancidity:

• Rancid – Fat/oil containing food waste /unpleasant smell when it is kept for a long time
• This happens due to oxidation reaction
• Substances that prevent oxidation are called as antioxidant are added to foods containing fat/oil
• Keep food in air tight container will slow down the process of oxidation
• Chips company flush the chips packet with nitrogen to prevent chips from being oxidised

Class 10 Chemical Reactions and Equations Activity Questions with answers

Activity 1.1

Burning of Magnesium Ribbon in air

Observation:

• When magnesium ribbon is burned, it burns with a bright white flame.
• After burning, it leaves behind a white powdery ash in the watch-glass.

Explanation:

• This is a combination reaction where magnesium reacts with oxygen in the air to form magnesium oxide (MgO).
• The white ash is magnesium oxide, a basic oxide.

Chemical Equation:

2Mg (s) + O₂ (g) → 2MgO (s)

Activity 1.2

Lead nitrate and Potassium Iodide

Observation:

• When potassium iodide solution is added to lead nitrate solution, a bright yellow precipitate is formed immediately.

Explanation:

• This is a double displacement reaction.
• Lead(II) iodide (PbI₂) is formed as an insoluble yellow precipitate, and potassium nitrate (KNO₃) remains in solution.
• This is also called a precipitation reaction.

Activity 1.3

Zinc and Dilute Sulphuric acid

Observation:

• When dilute hydrochloric acid or sulphuric acid is added to zinc granules, bubbles (effervescence) are seen around the zinc.
• A gas is evolved.
• On touching the flask or test tube, it feels warm.

Explanation:

• This is a chemical reaction between zinc and dilute acid, producing hydrogen gas.
• The reaction is exothermic, so heat is released, causing a rise in temperature.
• The bubbles are due to the evolution of hydrogen gas.

Chemical Equation:

With hydrochloric acid:
Zn (s) + 2HCl (aq) → ZnCl₂ (aq) + H₂ (g)

With sulphuric acid:
Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)

Chemical Equation:

Pb(NO₃)₂ (aq) + 2KI (aq) → PbI₂ (s) ↓ + 2KNO₃ (aq)

Activity 1.4

Formation of slaked lime by the reaction of calcium oxide with water

Observation:

• When water is added to calcium oxide (quick lime), a hissing sound is heard.
• A white, slaked suspension is formed.
• On touching the beaker, it feels hot

Explanation:

• This is an exothermic reaction, which releases heat.
• Calcium oxide reacts with water to form calcium hydroxide (slaked lime), and heat is produced in the process.

Chemical Equation:

CaO (s) + H₂O (l) → Ca(OH)₂ (aq) + heat

Activity 1.5

Heating of Ferrous sulphate

Observation:

• Before heating: Ferrous sulphate crystals are green in colour.
• After heating:
  • The crystals first turn white as water of crystallization is lost.
  • On further heating, they turn brown and emit a smell of burning sulphur (like rotten eggs).

Explanation:

• This is a thermal decomposition reaction.
• On heating, ferrous sulphate (FeSO₄·7H₂O) loses water and decomposes to form:
  • Ferric oxide (Fe₂O₃) – brown solid
  • Sulphur dioxide (SO₂) and sulphur trioxide (SO₃) – gases with a pungent smell

Chemical Equation:

2FeSO₄ (s) → Fe₂O₃ (s) + SO₂ (g) + SO₃ (g)
(on heating)

Activity 1.6

Heating of Lead nitrate and emission of Nitrogen dioxide

Observation:

• On heating, lead nitrate starts to decompose.
• A brown gas is released.
• A yellow residue is left behind in the boiling tube.

Explanation:

• This is a thermal decomposition reaction.
• On heating, lead nitrate (Pb(NO₃)₂) breaks down to form:
  • Lead oxide (PbO) – yellow solid
  • Nitrogen dioxide (NO₂) – brown gas
  • Oxygen (O₂) – colourless gas

Chemical Equation:

2Pb(NO₃)₂ (s) → 2PbO (s) + 4NO₂ (g) + O₂ (g)
(on heating)

Activity 1.7

Electrolyis of water

Observation:

• Bubbles are formed at both electrodes after switching on the current.
• The volume of gas collected is different in the two test tubes:
  • One test tube collects twice the volume of gas as the other.
• When a burning candle is brought near the gas:
  • In one test tube, the gas burns with a 'pop' sound.
  • In the other, the candle glows brighter.

Explanation:

• This is an example of electrolysis of water.
• Water (H₂O) breaks down into hydrogen and oxygen gases.
• The gas that burns with a pop sound is hydrogen.
• The gas that supports combustion and makes the flame brighter is oxygen.
• Since water has two parts of hydrogen and one part of oxygen, the volume of hydrogen collected is twice that of oxygen.

Chemical Equation:

2H₂O (l) → 2H₂ (g) + O₂ (g)
(by electrolysis)

Activity 1.8

Silver chloride turns grey in sunlight to form silver metal

Observation:

• Initially, silver chloride is white in colour.
• After exposure to sunlight, it turns grey.

Explanation:

• This is a photochemical decomposition reaction.
• In sunlight, silver chloride breaks down into silver metal and chlorine gas.
• The grey colour appears because of the formation of metallic silver.

Chemical Equation:
2AgCl (s) → 2Ag (s) + Cl₂ (g) [in presence of sunlight]

Activity 1.9

1. Iron nails dipped in copper sulphate solution
2. Iron nails and copper sulphate solutions compared before and after the experiment

:Observation:

• The blue colour of copper sulphate solution in test tube B becomes fainter compared to test tube A.
• The iron nails kept in test tube B get a reddish-brown coating.
• The iron nail kept aside remains unchanged.

Explanation:

• This is a displacement reaction.
• Iron is more reactive than copper, so it displaces copper from copper sulphate solution.
• The displaced copper gets deposited on the iron nails, giving them a reddish-brown coating.
• Due to the removal of copper from the solution, the blue colour of copper sulphate fades.

Chemical Equation:

Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

Activity 1.10

Formation of Barium sulphate and Sodium Chloride

Observation:

• When sodium sulphate solution is mixed with barium chloride solution, a white precipitate is formed.

Explanation:

• This is a double displacement reaction.
• A white insoluble substance, barium sulphate (BaSO₄), is formed as a precipitate.
• This type of reaction is also called a precipitation reaction.

Chemical Equation:

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

Activity 1.11

Oxidation of Copper to Copper oxide

Observation:

• On heating, the reddish-brown copper powder turns black.

Explanation:

• This is a combination reaction where copper reacts with oxygen in the air to form copper(II) oxide (CuO).
• The black coating is due to the formation of copper oxide

Chemical Equation:

2Cu (s) + O₂ (g) → 2CuO (s)

Intext Pg.10

1. (i) Name the substance ‘X’ and write its formula:

• The substance ‘X’ used for whitewashing is calcium oxide.
• Formula: CaO

(ii) Reaction of calcium oxide with water:

CaO (s) + H₂O (l) → Ca(OH)₂ (aq) + heat

• This reaction forms calcium hydroxide (slaked lime), which is used in whitewashing.
• The solution reacts with carbon dioxide in the air to form a shiny white coating of calcium carbonate on walls.

2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

• In Activity 1.7 (Electrolysis of water), water decomposes into hydrogen and oxygen gases.
• The volume of hydrogen gas is double that of oxygen gas because each water molecule (H₂O) has two hydrogen atoms and one oxygen atom.
• Hence, twice the amount of hydrogen is released compared to oxygen.
• Name of the gas with double volume: Hydrogen gas (H₂)

Intext 1:Pg 6

1. Why should a magnesium ribbon be cleaned before burning in air?

Magnesium ribbon is cleaned before burning to remove the layer of magnesium oxide (MgO) that forms on its surface due to reaction with atmospheric oxygen. This ensures that magnesium burns efficiently in air.

2. Balanced Chemical Equations

(i) Hydrogen + Chlorine → Hydrogen chloride

H₂+Cl₂→2HCl

(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

3BaCl₂+Al₂(SO4)₃→3BaSO₄+2AlCl₃

(iii) Sodium + Water → Sodium hydroxide + Hydrogen

2Na+2H2O→2NaOH+H2↑2Na + 2H₂O → 2NaOH + H₂ ↑

3. Balanced Chemical Equations with State Symbols

(i) Barium chloride and sodium sulphate in water react to form barium sulphate (insoluble) and sodium chloride (soluble):

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

(ii) Sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water:

NaOH(aq)+HCl(aq)→NaCl(aq)+H2O(l)

Intext Pg 13

1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

• Iron is more reactive than copper.
• When an iron nail is dipped in copper sulphate solution, iron displaces copper from the solution.
• As a result:
  • Copper gets deposited on the iron nail (reddish-brown layer), and
  • The blue colour of copper sulphate fades due to the formation of colourless iron sulphate.

Reaction:
Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

2. Give an example of a double displacement reaction other than the one given in Activity 1.10.

Example:
When sodium carbonate reacts with calcium chloride:

Na₂CO₃ (aq) + CaCl₂ (aq) → CaCO₃ (s) ↓ + 2NaCl (aq)

• A white precipitate of calcium carbonate is formed.
• This is a double displacement and precipitation reaction.

3. Identify the substances that are oxidised and reduced:

(i) 4Na(s) + O₂(g) → 2Na₂O(s)

• Sodium (Na) is oxidised to sodium oxide (Na₂O).
• Oxygen (O₂) is reduced to oxide ion (O²⁻).

Oxidised: Sodium (Na)

 Reduced: Oxygen (O₂)

(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)

• Hydrogen (H₂) is oxidised to water (H₂O).
• Copper oxide (CuO) is reduced to copper (Cu).

Oxidised: Hydrogen (H₂)
 Reduced: Copper oxide (CuO)

Welcome to your Class 10 Chemical Compound Names and Formula

Name

Email

Which compound is Calcium chloride?

CaCO₃

CaO

CaCl₂

None

Which compound contains chloride ion (Cl⁻)?

ZnSO₄

NaCl

NaNO₃

None

Which of the following is Barium chloride?

BaCl₂

BaSO₄

BaO

None

Which compound contains Zinc and sulphate?

ZnO

ZnSO₄

ZnCl₂

None

Which compound is Copper sulphate?

CuO

CuSO₄

CuCl₂

None

Which compound is Sodium carbonate?

NaNO₃

NaCl

Na₂CO₃

None

Which compound is Sodium hydroxide?

Na₂SO₄

NaOH

NaCl

None

Which compound belongs to nitrates?

NaNO₃

NaCl

Na₂CO₃

None

Which compound is Silver chloride?

AgNO₃

AgCl

AgBr

None

Which compound is Silver bromide?

AgCl

AgNO₃

AgBr

None

Which compound contains potassium and nitrate?

KI

KNO₃

KCl

None

Which compound is Potassium iodide?

KNO₃

NaI

KI

None

Which compound is Sulphuric acid?

HNO₃

H₂SO₄

HCl

None

Which acid contains chlorine?

HCl

HNO₃

H₂SO₄

None

Which acid contains nitrate ion?

H₂SO₄

HNO₃

HCl

None

Which compound is Ferrous sulphide?

FeO

FeCl₂

FeS

None

Which compound is a sulphide gas?

HCl

H₂S

NO₂

None

Which compound is Lead oxide?

PbO

PbI₂

PbCl₂

None

Which compound is Calcium oxide?

CaCl₂

CaSO₄

CaO

None

Which compound is Magnesium oxide?

MgCl₂

MgSO₄

MgO

None

Which compound is Copper oxide?

CuSO₄

CuO

CuCl₂

None

Which compound is Zinc oxide?

ZnCl₂

ZnSO₄

ZnO

None

Which compound is Nitrogen dioxide?

NO₂

N₂O

NO

None

Which compound is Lead nitrate?

PbCl₂

Pb(NO₃)₂

PbO

None

Which compound contains carbonate ion (CO₃²⁻)?

NaNO₃

NaCl

Na₂CO₃

None

Which compound contains sulphate ion (SO₄²⁻)?

NaNO₃

Na₂SO₄

NaCl

None

Which compound contains chloride ion?

ZnSO₄

ZnO

ZnCl₂

None

Which compound contains iodine?

KI

KNO₃

NaCl

None

Which compound belongs to silver compounds?

NaNO₃

AgNO₃

KNO₃

None

Which compound forms a yellow precipitate in reactions?

PbO

PbI₂

Pb(NO₃)₂

None

Time's up

Useful links:

CBSE CLASS 6 SOCIAL SCIENCE

CBSE CLASS 6 SCIENCE

CBSE CLASS 7 SOCIAL STUDIES

CBSE CLASS 7 MATHS

CBSE CLASS 8 MATHS

CBSE CLASS 8 SCIENC

Chemical Equations

Chemical reactions play a crucial role in our daily lives. From cooking food to rusting iron, chemical reactions are happening all around us. In CBSE Class 10 Science, the chapter "Chemical Reactions and Equations" introduces students to the fundamentals of how substances interact and transform.

This blog post provides detailed notes, explanations, and examples to help students understand the topic effectively and score full marks in their exams.

Activity 1.1

1. Mg Ribbon (3-4 cm) rubbed with sandpaper

2. Hold it with tongs.

3. Burn it using a burner and collect the ash.

Inference: 

• Burning of Mg in air forms Magnesium oxide.
• Equation:
• 2Mg + O₂ → 2MgO
• (Reactants) → (Product)

A chemical reaction has taken place and resulted in the formation of MgO.

If there is:

• Change in state

• Change in colour

• Evolution of gas

• Change in temperature

Then a chemical reaction has taken place.

Chemical Equation:

• It represents a chemical reaction.
• LHS: Reactants
• RHS: Products

Balanced Equation:

• The number of atoms of each element should be equal on both sides.

• 2Mg + O₂ → 2MgO

Law of Conservation of Mass:

• Mass can neither be created nor destroyed.
• The total mass of elements present in the product of a chemical reaction has to be equal to the total mass of elements present in the reactants.
• In other words, the number of atoms of each element remains the same before and after the chemical reaction.

Example 1:

Zn + H₂SO₄ → ZnSO₄ + H₂↑ 

So this is a balanced chemical equation.

Example 2:

Fe + H₂O → Fe₃O₄ + H₂

Steps to balance the equation:

1. Fe + H₂O → Fe₃O₄ + H₂

2. 3Fe + H₂O → Fe₃O₄ + H₂

3. 3Fe + 4H₂O → Fe₃O₄ + H₂

4. 3Fe + 4H₂O → Fe₃O₄ + 4H₂

Now, the equation is balanced.

Physical States in Chemical Equations:

To make the chemical equation more informative, the physical states of reactants and products are mentioned as:

• (s) = Solid

• (g) = Gaseous

• (aq) = Aqueous (Liquid)

• When (g) is used in H₂O, it indicates that a chemical reaction takes place using steam instead of liquid water.

Indicating Conditions in Reactions:

Sometimes, temperature, pressure, and catalysts are indicated above or below the arrow in the equation.

Example:

CO (g) + H₂ (g) → CH₃OH (at 340 atm)

Photosynthesis Reaction:

CO₂ (aq) + H₂O (aq) → C₆H₁₂O₆ (aq) + O₂ (g) + H₂O (aq)

(Occurs in sunlight with chlorophyll)

Catalyst in Chemical Reactions:

A catalyst is a chemical substance that speeds up a chemical reaction without reacting with the reactants or products.

Example:

Potassium permanganate (KMnO₄) is used in the decomposition of hydrogen peroxide into water and oxygen.

Reaction:

H₂O₂ (aq) → H₂O (l) + O₂ (g) (KMnO₄ as catalyst)

Types of Chemical Reactions

Combination Reactions:

When two or more substances (elements or compounds) combine to form a single product, the reactions are called combination reactions.

Example:
CaO (s) + H₂O (l) → Ca(OH)₂ (aq) + Heat

Quicklime + Water → Slaked Lime

C (s) + O₂ (g) → CO₂ (g)

2H₂ (g) + O₂ (g) → 2H₂O (g)

Exothermic Reactions:

Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.

Burning of Natural Gas:

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g)

(Methane)

Welcome to your Class 10 Chemical Compound Names and Formula

Name

Email

Which compound is Calcium chloride?

CaCO₃

CaO

CaCl₂

None

Which compound contains chloride ion (Cl⁻)?

ZnSO₄

NaCl

NaNO₃

None

Which of the following is Barium chloride?

BaCl₂

BaSO₄

BaO

None

Which compound contains Zinc and sulphate?

ZnO

ZnSO₄

ZnCl₂

None

Which compound is Copper sulphate?

CuO

CuSO₄

CuCl₂

None

Which compound is Sodium carbonate?

NaNO₃

NaCl

Na₂CO₃

None

Which compound is Sodium hydroxide?

Na₂SO₄

NaOH

NaCl

None

Which compound belongs to nitrates?

NaNO₃

NaCl

Na₂CO₃

None

Which compound is Silver chloride?

AgNO₃

AgCl

AgBr

None

Which compound is Silver bromide?

AgCl

AgNO₃

AgBr

None

Which compound contains potassium and nitrate?

KI

KNO₃

KCl

None

Which compound is Potassium iodide?

KNO₃

NaI

KI

None

Which compound is Sulphuric acid?

HNO₃

H₂SO₄

HCl

None

Which acid contains chlorine?

HCl

HNO₃

H₂SO₄

None

Which acid contains nitrate ion?

H₂SO₄

HNO₃

HCl

None

Which compound is Ferrous sulphide?

FeO

FeCl₂

FeS

None

Which compound is a sulphide gas?

HCl

H₂S

NO₂

None

Which compound is Lead oxide?

PbO

PbI₂

PbCl₂

None

Which compound is Calcium oxide?

CaCl₂

CaSO₄

CaO

None

Which compound is Magnesium oxide?

MgCl₂

MgSO₄

MgO

None

Which compound is Copper oxide?

CuSO₄

CuO

CuCl₂

None

Which compound is Zinc oxide?

ZnCl₂

ZnSO₄

ZnO

None

Which compound is Nitrogen dioxide?

NO₂

N₂O

NO

None

Which compound is Lead nitrate?

PbCl₂

Pb(NO₃)₂

PbO

None

Which compound contains carbonate ion (CO₃²⁻)?

NaNO₃

NaCl

Na₂CO₃

None

Which compound contains sulphate ion (SO₄²⁻)?

NaNO₃

Na₂SO₄

NaCl

None

Which compound contains chloride ion?

ZnSO₄

ZnO

ZnCl₂

None

Which compound contains iodine?

KI

KNO₃

NaCl

None

Which compound belongs to silver compounds?

NaNO₃

AgNO₃

KNO₃

None

Which compound forms a yellow precipitate in reactions?

PbO

PbI₂

Pb(NO₃)₂

None

Time's up

Useful links:

CBSE CLASS 6 SOCIAL SCIENCE

CBSE CLASS 6 SCIENCE

CBSE CLASS 7 SOCIAL STUDIES

CBSE CLASS 7 MATHS

CBSE CLASS 8 MATHS

CBSE CLASS 8 SCIENC