UNIT-I : CHEMICAL SUBSTANCES—NATURE AND BEHAVIOUR
Chapter-1
Chemical Reactions and Equations
1 Chemical Reactions
Concept covered:
chemical equation.
l Chemical reaction and examples l Skeletal and balanced chemical equation l Steps to balance a
Chemical Reaction [Board, 2020] Writing a Chemical Equation:
• A chemical reaction is a process in Chemical (i) The symbols of elements and the formulae of reacting
2
which the original substance(s) loses Reactions substances (reactants) are written on the left-hand side
its nature and identity and forms new of the equation, with a plus (+) sign between them.
substance(s) with different properties. (ii) The symbols and formulae of the substances formed
• Breaking of the chemical bonds and (products) are written on the right-hand side of the
formation of new chemical bonds
equation, with a plus sign (+) between them.
'results in a' or 'causes' a chemical
reaction. Scan Me! (iii) An arrow sign (→) is put between the reactants and
3
• The substances that take part in a the products.
chemical reaction are called Reactants. (iv) The physical states of the reactants and products are
• The substances that are formed in a chemical reaction also mentioned in a chemical equation.
are called Products. Skeletal Chemical Equation: A chemical equation which
• A chemical reaction can be identified by either of the simply represents the symbols and formulae of reactants
following observations: [Board, 2024] and products taking part in the reaction is known as
S. No. Characteristics Examples skeletal chemical equation for a reaction.
4
1. Change in The combustion reaction of For example: Mg + O2 → MgO is a skeletal equation.
state candle wax is characterised by Balanced Equation: The equation in which atoms of
[Board, 2024] a change in state from solid to various elements on both sides of a chemical equation
liquid and gas. are equal in accordance with the Law of Conservation of
2. Change in The chemical reaction between Mass. [Board, 2024]
colour citric acid and purple-coloured For example:
potassium permanganate solution 340 atm
(i) CO(g) + 2H2 (g)
CH3OH(l)
is characterised by a change in
colour from purple to colourless.
(ii) 6CO2(g) + 12H2O(l)
sunlight
C6H12O6(aq) + 6O2 (aq)
chlorophyll
3. Evolution of The chemical reaction between
Glucose + 6 H2O (l)
gas zinc and dilute sulphuric acid is
characterised by hydrogen gas. The process of equalising the atoms of the elements on
Zn(s) + H2SO4(aq) → ZnSO4(aq) + both sides of an equation is called balancing a chemical
H2 ↑ (g) equation. This is known as hit and trial method. Let
4. Change in The reaction between quicklime us understand this with the help of an example given
temperature and water to form slaked lime is below:
characterised by an increase in
temperature. Example 1
CaO +H2O → Ca(OH)2 + Heat
5. Formation of When an aqueous solution of Balancing a chemical equation:
a precipitate sodium sulphate is mixed with Step 1: Write the chemical equation.
the aqueous solution of barium
Fe + H2O → Fe3O4 + H2
chloride, barium sulphate comes
in the form of white precipitate. Step 2: Count the number of atoms of each element on
Na2SO4 (aq) + BaCl2 (aq) → both sides of the chemical equation.
BaSO4(↓)+2NaCl(aq) No. of atoms at No. of atoms at
Element
Chemical Equations [Board, 2016] reactant side product side
• A chemical equation is the symbolic representation of a 1. Fe 1 3
chemical reaction in the form of symbols and formulae. 2. H 2 2
• It is a way to represent the chemical reaction in a concise 3. O 1 4
and informative way.
Step 3: Equalise the number of atoms of element with
• For example,
Magnesium + Oxygen → Magnesium oxide the maximum number by trial and error method 'by
(Reactants) (Product) placing it in front of it.' Fe + 4H2O → Fe3O4 + H2
This equation is called word equation. Step 4: Try to equalise all the atoms of elements on both
• The word equation can be converted into chemical reactant and product sides by adding coefficient in
equation by writing symbols and formulae of the front of it. 3Fe + 4H2O → Fe3O4 + 4H2
substance instead of their names 2Mg + O2 → 2MgO
, 1
2 | Oswaal CBSE Question Bank | SCIENCE | Class 10
Types of Chemical Reactions
2 Concept covered: l Combination reaction l Decomposition reaction l Displacement reaction l Double displacement reaction l Redox reaction
l Oxidation and reduction reaction l Exothermic and endothermic reaction.
Types of Chemical Reactions White precipitate of BaSO4 is formed,
3
I. Combination Reaction: The reaction in which two or so it is also called precipitation Precipitation reaction:
ons
more reactants combine to form a single product. e.g., rection. Precipitation reacti
and
(i) Burning of coal V. Oxidation and Reduction: occur when cations
C(s) + O2(g) → CO2(g) an ion s in aqueous solu-
Loss of electron/s is called
bine to form an
(ii) Formation of water Oxidation and gain of electron/s is tion com ionic solid called
insoluble
2H2(g) + O2(g) → 2H2O(l) call Reduction.
a precipitate. e.g.,
Oxidation: It is a process of gaining
4
(iii) CaO(s) + H2O(l) → Ca(OH)2 (aq) + Heat NaCl + AgNO3 →A
gCl +
oxygen or loss of hydrogen atom NaNO3 (Precipitat
e)
(Quicklime) (Slaked lime)
during a reaction by an atom,
Exothermic Reactions: Reaction in which heat is released
molecule, or ion. When any atom
along with the formation of products e.g., loses electron or increase in oxidation number is observed
(i) Burning of natural gas. by another atom, ion or molecule, it is said to be oxidation.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + Heat
(ii) Respiration is also an exothermic reaction. 2Cu + O2 Heat
2CuO [Board, 2019]
C6H12O6(s) + 6O2(g) → 6CO2(aq) + 6H2O(l) + Energy Reduction: It is a process of gaining hydrogen or loss of
(Glucose) oxygen atom during a reaction by an atom, molecule, or
II. Decomposition Reaction: [Board 2024]
ion. When any atom gain electron or decrease in oxidation
number is observed by another atom, ion or molecule, it
The reaction in which a compound splits into two or more
is said to be reduction.
simpler substances is called decomposition reaction.
CuO + H2 → Cu + H2O
A→B+C
(a) Thermal Decomposition: When decomposition is MNEMONICS
carried out by heating. e.g.,
Concept 1: Types of decomposition reaction
(i) 2FeSO4(s) Heat
Fe2O3(s) + SO2(g) + SO3(g)
Mnemonics: PET
(Ferrous sulphate) (Ferric oxide)
Interpretations:
Green colour Red-brown colour
PET: Photolytic reaction, Electrolytic reaction, Thermal reac-
(ii) CaCO3(s) Heat
CaO(s) + CO2(g) tion
(Lime stone) (Quicklime) Concept 2: Oxidation and reduction reaction
(b) Electrolytic decomposition: When decomposition is Mnemonics: OIL RIG
carried out by passing electricity. e.g., Interpretations:
Electric OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain
2H2O(l) current
2H2(g) + O2(g) of electrons
(c) Photolytic decomposition: When decomposition is Concept 3: Types of chemical reactions
carried out in presence of sunlight. e.g., Mnemonics: ROC.D3
Sunlight Interpretations:
(i) 2AgCl(s)
2Ag(s) + Cl2(g)
ROC.D3: Reduction, Oxidation, Combination, Decomposi-
Sunlight
(ii) 2AgBr(s)
2Ag(s) + Br2(g) tion, Displacement, Double Displacement
Endothermic Reaction: The reactions which require Redox (Oxidation and Reduction) Reaction: In this
energy in the form of heat, light or electricity to break reaction, CuO is reduced to Cu and H2 is oxidised to
reactants are called endothermic reactions. e.g., H2O. In other words, one reactant gets oxidised while the
(i) NH4Cl (s) + H2O (l) → NH4Cl (aq) – Heat other gets reduced. Such reactions are called oxidation–
III. Displacement Reaction: The chemical reactions reduction reactions or redox reactions. [Board 2024]
in which more reactive element displaces less reactive
element from its salt solution. e.g.,
(i) Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
(Iron) (Copper sulphate) (Ferrous sulphate) (Copper)
(ii) Zinc displaces copper forming zinc sulphate.
Zinc is more reactive than copper.
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) A redox (oxidation-reduction)reaction in- Oxidation and
(Zinc Sulphate) volves the transfer of electrons between Reduction
IV. Double Displacement Reaction: A reaction in which
reactants. Oxidation involves the loss of
new compounds are formed by mutual exchange of ions
electrons, while reduction involves the
between two compounds. e.g.,
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) gain of electrons. [Board, 2023]
(Sodium (Barium (Barium (Sodium
Scan Me!
sulphate) chloride) sulphate) chloride)
, Revision Notes | 3
Chapter-2
Acids, Bases and Salts
1 Acids and Bases
Concept covered: l Definition of acids and bases l Properties of acids and bases l Indicators and its type l pH scale and
importance of pH in everyday life.
Acids
• Acids are the substances that furnish H+ ions in aqueous For Bases: It changes colour to green in bases.
2
solution. Acids are sour in taste. They turn blue litmus red. (iii) Turmeric: For Acids: It remains yellow in acids.
• Its examples include: Sulphuric acid (H2SO4), Acetic For Bases: It changes colour to red in bases.
acid (CH3COOH), Nitric acid (HNO3), etc. 2. Synthetic Indicators: These are the indicators which
• If in an aqueous solution, concentration of acid is low changes their colour in bases and acids, but made synthetically.
as compared to water, it is called dilute solution and if Example: Methyl Orange, Phenolphthalein
concentration of acid is high, it is called concentrated (i) Phenolphthalein: For Acids: It remains colourless
3
solution. in acids.
• Acids which dissociate into ions completely are called For Bases: It changes colour to pink in bases.
strong acids, e.g., H2SO4, HCl, HNO3, etc. (ii) Methyl Orange: For Acids: It changes colour to red
in acids
• Acids which do not dissociate into ions completely are
called weak acids, e.g., citric acid, acetic acid, formic acid, For Bases: It changes colour to yellow in bases.
etc. 3. Olfactory Indicators: These are the indicators which
4
changes their smell in bases and acids
Note: Example: Onion ,Clove oil, Vanilla Extract
Although we talk about ‘taste’ of acids and bases, (i) Onion: For Acids: Its smell retains in acids.
it is not advisable to taste any acid or base. Most of For Bases: It loses its smell in bases.
them are harmful. Similarly, touching the solutions (ii) Vanilla Extract: For Acids: Its smell retains in acids.
of strong acids and bases should be avoided. They
For Bases: It loses its smell in bases.
may harm the skin.
(iii) Clove Oil: For Acids: Its smell retains in acids.
Bases For Bases: It loses its smell in bases.
• Bases are those chemical compounds Acid, Bases and • Chemical Properties of Acids and Bases: [Board 2018]
which are bitter in taste, soapy in touch, Salts
1. Reaction of Metals with: [Board 2024]
turn red litmus blue and give OH– ions
in aqueous solution. Acids Bases
• The examples include sodium Acid + Metal → Salt + Base + Metal → Salt +
hydroxide (NaOH), potassium Hydrogen gas Hydrogen gas
hydroxide (KOH), etc. Scan Me! e.g., 2HCl + Zn e.g., 2NaOH + Zn
• The substances/bases which ionise → ZnCl2 + H2(g) → Na2ZnO2 + H2(g)
completely to furnish OH- ions are called strong bases, Zinc chloride Sodium zincate
e.g., KOH, NaOH, etc.
Test for H2 gas: Hydrogen gas released can be tested by
• The bases which ionise only partially are called weak
bringing a burning candle near gas bubbles; it bursts with
bases, e.g., Mg(OH)2, Cu(OH)2, etc.
pop sound. [Board 2024]
• Both acids and bases conduct electricity in their aqueous
2. Reaction of Metal Carbonates/Metal Hydrogen
solution due to the presence of free ions.
Carbonates with:
• Indicators: These are the substances which change their
colour/smell in different acids or bases. Acids Bases
• Identification using indicators: Acid + Metal Carbonate Base + Metal Carbonate
There are different type of indicators used to distinguish /Metal Hydrogen /Metal Hydrogen
between acids and bases Carbonate Carbonate
1. Natural Indicators: These are the indicators which changes ↓ ↓
their colour in bases and acids,but extracted naturally.
Example: Turmeric, Litmus, China rose Salt + CO2(g) + H2O No Reaction
(i) Litmus Paper: For Acids: Blue litmus paper changes e.g., 2HCl + Na2CO3 → 2NaCl + CO2(g) + H2O
colour to red in acids. HCl + NaHCO3 → NaCl + CO2(g) + H2O
For Bases: Red litmus paper changes colour to blue in Test for CO2: CO2 can be tested by passing it through
bases. lime water. Lime water turns milky due to formation of
(ii) China Rose: For Acids: It changes colour to red in insoluble calcium carbonate (white precipitate).
acids. Ca(OH)2 + CO2 → CaCO3 + H2O
, 4 | Oswaal CBSE Question Bank | SCIENCE | Class 10
When excess CO2 is passed, milkiness disappears due to • Similarly, substances which when dissolved in water
formation of soluble calcium hydrogen-carbonate. ionise to produce hydroxide ions, OH– (aq).
CaCO3 + CO2 + H2O → Ca(HCO3)2 Examples: When sodium hydroxide is dissolved in water, it
3. Reaction of Acids and Bases with Each Other dissociates into hydroxide and sodium ion.
When an acid reacts with base, the hydrogen ion of acid
combines with hydroxide ion of base and forms water. As NaOH(s) Na+(aq) + OH– (aq)
these ions combine together, they form water instead of 4. Reaction of Acids with Metal Oxides:
remaining free, thus both neutralise each other. Metal oxides react with acids to give salt and water.
Acid + Base → Salt + Water [Board 2024] Metal oxide + Acid → Salt + Water
Since in the reaction between an acid and Properties of Example: Copper oxide reacts with dilute hydrochloric acid
a base both neutralise each other, it is also Acids and Bases to form copper chloride (salt) and water.
known as neutralisation reaction.
Example: Sodium hydroxide (a strong CuO + 2HCl(dil.) → CuCl2 + H2O
base) reacts with hydrochloric acid to form Copper oxide Copper chloride
sodium chloride and water. Copper oxide is black in colour. When dilute hydrochloric
NaOH(aq) + HCl(aq) → NaCl(aq) + acid is added to it, the colour of the solution becomes blue-
Scan Me!
H2O(l) green due to the formation of copper chloride.
4. Reaction of Metallic Oxides with Acids: How Strong Are Acid or Base Solutions?
When metallic oxides react with acids, formation of salt
and water takes place. • Strength of an acid or base depends on the number of
Metal Oxide + Acid → Salt + Water H+ ions or OH– ions produced by them respectively.
For Example: Copper oxide reacts with hydrochloric • Based on its ability to dissociate into ions in the solution,
acid, formation of copper chloride and water take place acids and bases are classified as strong acid or base and
CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l) weak acid or base.
5. Reaction of Non-Metallic Oxides with Basess: (a) Strong Acids: Acids that completely dissociate in
When non-metallic oxides react with bases, formation of water to produce large amount of hydrogen ions are
salt and water takes place. called strong acids. For example, hydrochloric acid
Non-Metal Oxide + Base → Salt + Water (HCl), sulphuric acid (H2SO4), nitric acid (HNO3) are
For Example: Carbon dioxide reacts with calcium strong acids as they get completely ionised in water to
hydroxide, formation of calcium carbonate and water form ions.
take place
HCl (aq) → H+(aq) + Cl– (aq)
Ca(OH)2(s) + CO2(aq) + → CaCO3(s) + H2O(l)
Common Properties of All Acids and Bases [Board 2024] (b) Weak Acids: Acids which get partially ionised in
water to produce small amount of hydrogen ions are
• Acids give hydrogen gas when they react with metal. known as weak acids. For example, acetic acid partially
This shows that all acids contain hydrogen. dissociates in water to produce small amount of
• When acids are dissolved in water they dissociate as hydrogen ions.
H+ ions. The dissociation of hydrogen ions in aqueous CH3COOH (aq) → H+ (aq) + CH3COO–(aq)
solution is the common property of all acids. As a result,
(c) Strong Bases: Bases which completely ionise in
an acid shows acidic behaviour.
water to produce large amount of hydroxide ions are
HCl (aq) → H+(aq) + Cl– (aq)
called strong bases. Examples include NaOH, KOH, etc.
HNO3(aq) → H+(aq) + NO3– (aq)
(d) Weak Bases: Bases which partially pH Scale
CH3COOH (aq) → H+ (aq) + CH3COO– (aq) dissociate in water to furnish lesser
• As H+ ion cannot exist alone, it combines with water amount of hydroxide ions are called
molecules and forms H3O+ (hydronium) ions. weak bases. Examples include
Example: ammonium hydroxide (NH4OH) and
HCl + H2O → H3O+ + Cl– calcium hydroxide Ca(OH)2.
Scan Me!
H+ + H2O → H3O+ pH
The concentration of H+ is generally
Thus, acids can also be defined as substances, which when small, therefore concentrations of H+ pH: A scale for measu
ring
dissolved in water ionise to produce hydrogen ions, H+ (aq). is expressed in terms of pH. H+ ion con cen tra tio n in
a solution..
Key Diagram
Chapter-1
Chemical Reactions and Equations
1 Chemical Reactions
Concept covered:
chemical equation.
l Chemical reaction and examples l Skeletal and balanced chemical equation l Steps to balance a
Chemical Reaction [Board, 2020] Writing a Chemical Equation:
• A chemical reaction is a process in Chemical (i) The symbols of elements and the formulae of reacting
2
which the original substance(s) loses Reactions substances (reactants) are written on the left-hand side
its nature and identity and forms new of the equation, with a plus (+) sign between them.
substance(s) with different properties. (ii) The symbols and formulae of the substances formed
• Breaking of the chemical bonds and (products) are written on the right-hand side of the
formation of new chemical bonds
equation, with a plus sign (+) between them.
'results in a' or 'causes' a chemical
reaction. Scan Me! (iii) An arrow sign (→) is put between the reactants and
3
• The substances that take part in a the products.
chemical reaction are called Reactants. (iv) The physical states of the reactants and products are
• The substances that are formed in a chemical reaction also mentioned in a chemical equation.
are called Products. Skeletal Chemical Equation: A chemical equation which
• A chemical reaction can be identified by either of the simply represents the symbols and formulae of reactants
following observations: [Board, 2024] and products taking part in the reaction is known as
S. No. Characteristics Examples skeletal chemical equation for a reaction.
4
1. Change in The combustion reaction of For example: Mg + O2 → MgO is a skeletal equation.
state candle wax is characterised by Balanced Equation: The equation in which atoms of
[Board, 2024] a change in state from solid to various elements on both sides of a chemical equation
liquid and gas. are equal in accordance with the Law of Conservation of
2. Change in The chemical reaction between Mass. [Board, 2024]
colour citric acid and purple-coloured For example:
potassium permanganate solution 340 atm
(i) CO(g) + 2H2 (g)
CH3OH(l)
is characterised by a change in
colour from purple to colourless.
(ii) 6CO2(g) + 12H2O(l)
sunlight
C6H12O6(aq) + 6O2 (aq)
chlorophyll
3. Evolution of The chemical reaction between
Glucose + 6 H2O (l)
gas zinc and dilute sulphuric acid is
characterised by hydrogen gas. The process of equalising the atoms of the elements on
Zn(s) + H2SO4(aq) → ZnSO4(aq) + both sides of an equation is called balancing a chemical
H2 ↑ (g) equation. This is known as hit and trial method. Let
4. Change in The reaction between quicklime us understand this with the help of an example given
temperature and water to form slaked lime is below:
characterised by an increase in
temperature. Example 1
CaO +H2O → Ca(OH)2 + Heat
5. Formation of When an aqueous solution of Balancing a chemical equation:
a precipitate sodium sulphate is mixed with Step 1: Write the chemical equation.
the aqueous solution of barium
Fe + H2O → Fe3O4 + H2
chloride, barium sulphate comes
in the form of white precipitate. Step 2: Count the number of atoms of each element on
Na2SO4 (aq) + BaCl2 (aq) → both sides of the chemical equation.
BaSO4(↓)+2NaCl(aq) No. of atoms at No. of atoms at
Element
Chemical Equations [Board, 2016] reactant side product side
• A chemical equation is the symbolic representation of a 1. Fe 1 3
chemical reaction in the form of symbols and formulae. 2. H 2 2
• It is a way to represent the chemical reaction in a concise 3. O 1 4
and informative way.
Step 3: Equalise the number of atoms of element with
• For example,
Magnesium + Oxygen → Magnesium oxide the maximum number by trial and error method 'by
(Reactants) (Product) placing it in front of it.' Fe + 4H2O → Fe3O4 + H2
This equation is called word equation. Step 4: Try to equalise all the atoms of elements on both
• The word equation can be converted into chemical reactant and product sides by adding coefficient in
equation by writing symbols and formulae of the front of it. 3Fe + 4H2O → Fe3O4 + 4H2
substance instead of their names 2Mg + O2 → 2MgO
, 1
2 | Oswaal CBSE Question Bank | SCIENCE | Class 10
Types of Chemical Reactions
2 Concept covered: l Combination reaction l Decomposition reaction l Displacement reaction l Double displacement reaction l Redox reaction
l Oxidation and reduction reaction l Exothermic and endothermic reaction.
Types of Chemical Reactions White precipitate of BaSO4 is formed,
3
I. Combination Reaction: The reaction in which two or so it is also called precipitation Precipitation reaction:
ons
more reactants combine to form a single product. e.g., rection. Precipitation reacti
and
(i) Burning of coal V. Oxidation and Reduction: occur when cations
C(s) + O2(g) → CO2(g) an ion s in aqueous solu-
Loss of electron/s is called
bine to form an
(ii) Formation of water Oxidation and gain of electron/s is tion com ionic solid called
insoluble
2H2(g) + O2(g) → 2H2O(l) call Reduction.
a precipitate. e.g.,
Oxidation: It is a process of gaining
4
(iii) CaO(s) + H2O(l) → Ca(OH)2 (aq) + Heat NaCl + AgNO3 →A
gCl +
oxygen or loss of hydrogen atom NaNO3 (Precipitat
e)
(Quicklime) (Slaked lime)
during a reaction by an atom,
Exothermic Reactions: Reaction in which heat is released
molecule, or ion. When any atom
along with the formation of products e.g., loses electron or increase in oxidation number is observed
(i) Burning of natural gas. by another atom, ion or molecule, it is said to be oxidation.
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + Heat
(ii) Respiration is also an exothermic reaction. 2Cu + O2 Heat
2CuO [Board, 2019]
C6H12O6(s) + 6O2(g) → 6CO2(aq) + 6H2O(l) + Energy Reduction: It is a process of gaining hydrogen or loss of
(Glucose) oxygen atom during a reaction by an atom, molecule, or
II. Decomposition Reaction: [Board 2024]
ion. When any atom gain electron or decrease in oxidation
number is observed by another atom, ion or molecule, it
The reaction in which a compound splits into two or more
is said to be reduction.
simpler substances is called decomposition reaction.
CuO + H2 → Cu + H2O
A→B+C
(a) Thermal Decomposition: When decomposition is MNEMONICS
carried out by heating. e.g.,
Concept 1: Types of decomposition reaction
(i) 2FeSO4(s) Heat
Fe2O3(s) + SO2(g) + SO3(g)
Mnemonics: PET
(Ferrous sulphate) (Ferric oxide)
Interpretations:
Green colour Red-brown colour
PET: Photolytic reaction, Electrolytic reaction, Thermal reac-
(ii) CaCO3(s) Heat
CaO(s) + CO2(g) tion
(Lime stone) (Quicklime) Concept 2: Oxidation and reduction reaction
(b) Electrolytic decomposition: When decomposition is Mnemonics: OIL RIG
carried out by passing electricity. e.g., Interpretations:
Electric OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain
2H2O(l) current
2H2(g) + O2(g) of electrons
(c) Photolytic decomposition: When decomposition is Concept 3: Types of chemical reactions
carried out in presence of sunlight. e.g., Mnemonics: ROC.D3
Sunlight Interpretations:
(i) 2AgCl(s)
2Ag(s) + Cl2(g)
ROC.D3: Reduction, Oxidation, Combination, Decomposi-
Sunlight
(ii) 2AgBr(s)
2Ag(s) + Br2(g) tion, Displacement, Double Displacement
Endothermic Reaction: The reactions which require Redox (Oxidation and Reduction) Reaction: In this
energy in the form of heat, light or electricity to break reaction, CuO is reduced to Cu and H2 is oxidised to
reactants are called endothermic reactions. e.g., H2O. In other words, one reactant gets oxidised while the
(i) NH4Cl (s) + H2O (l) → NH4Cl (aq) – Heat other gets reduced. Such reactions are called oxidation–
III. Displacement Reaction: The chemical reactions reduction reactions or redox reactions. [Board 2024]
in which more reactive element displaces less reactive
element from its salt solution. e.g.,
(i) Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
(Iron) (Copper sulphate) (Ferrous sulphate) (Copper)
(ii) Zinc displaces copper forming zinc sulphate.
Zinc is more reactive than copper.
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) A redox (oxidation-reduction)reaction in- Oxidation and
(Zinc Sulphate) volves the transfer of electrons between Reduction
IV. Double Displacement Reaction: A reaction in which
reactants. Oxidation involves the loss of
new compounds are formed by mutual exchange of ions
electrons, while reduction involves the
between two compounds. e.g.,
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) gain of electrons. [Board, 2023]
(Sodium (Barium (Barium (Sodium
Scan Me!
sulphate) chloride) sulphate) chloride)
, Revision Notes | 3
Chapter-2
Acids, Bases and Salts
1 Acids and Bases
Concept covered: l Definition of acids and bases l Properties of acids and bases l Indicators and its type l pH scale and
importance of pH in everyday life.
Acids
• Acids are the substances that furnish H+ ions in aqueous For Bases: It changes colour to green in bases.
2
solution. Acids are sour in taste. They turn blue litmus red. (iii) Turmeric: For Acids: It remains yellow in acids.
• Its examples include: Sulphuric acid (H2SO4), Acetic For Bases: It changes colour to red in bases.
acid (CH3COOH), Nitric acid (HNO3), etc. 2. Synthetic Indicators: These are the indicators which
• If in an aqueous solution, concentration of acid is low changes their colour in bases and acids, but made synthetically.
as compared to water, it is called dilute solution and if Example: Methyl Orange, Phenolphthalein
concentration of acid is high, it is called concentrated (i) Phenolphthalein: For Acids: It remains colourless
3
solution. in acids.
• Acids which dissociate into ions completely are called For Bases: It changes colour to pink in bases.
strong acids, e.g., H2SO4, HCl, HNO3, etc. (ii) Methyl Orange: For Acids: It changes colour to red
in acids
• Acids which do not dissociate into ions completely are
called weak acids, e.g., citric acid, acetic acid, formic acid, For Bases: It changes colour to yellow in bases.
etc. 3. Olfactory Indicators: These are the indicators which
4
changes their smell in bases and acids
Note: Example: Onion ,Clove oil, Vanilla Extract
Although we talk about ‘taste’ of acids and bases, (i) Onion: For Acids: Its smell retains in acids.
it is not advisable to taste any acid or base. Most of For Bases: It loses its smell in bases.
them are harmful. Similarly, touching the solutions (ii) Vanilla Extract: For Acids: Its smell retains in acids.
of strong acids and bases should be avoided. They
For Bases: It loses its smell in bases.
may harm the skin.
(iii) Clove Oil: For Acids: Its smell retains in acids.
Bases For Bases: It loses its smell in bases.
• Bases are those chemical compounds Acid, Bases and • Chemical Properties of Acids and Bases: [Board 2018]
which are bitter in taste, soapy in touch, Salts
1. Reaction of Metals with: [Board 2024]
turn red litmus blue and give OH– ions
in aqueous solution. Acids Bases
• The examples include sodium Acid + Metal → Salt + Base + Metal → Salt +
hydroxide (NaOH), potassium Hydrogen gas Hydrogen gas
hydroxide (KOH), etc. Scan Me! e.g., 2HCl + Zn e.g., 2NaOH + Zn
• The substances/bases which ionise → ZnCl2 + H2(g) → Na2ZnO2 + H2(g)
completely to furnish OH- ions are called strong bases, Zinc chloride Sodium zincate
e.g., KOH, NaOH, etc.
Test for H2 gas: Hydrogen gas released can be tested by
• The bases which ionise only partially are called weak
bringing a burning candle near gas bubbles; it bursts with
bases, e.g., Mg(OH)2, Cu(OH)2, etc.
pop sound. [Board 2024]
• Both acids and bases conduct electricity in their aqueous
2. Reaction of Metal Carbonates/Metal Hydrogen
solution due to the presence of free ions.
Carbonates with:
• Indicators: These are the substances which change their
colour/smell in different acids or bases. Acids Bases
• Identification using indicators: Acid + Metal Carbonate Base + Metal Carbonate
There are different type of indicators used to distinguish /Metal Hydrogen /Metal Hydrogen
between acids and bases Carbonate Carbonate
1. Natural Indicators: These are the indicators which changes ↓ ↓
their colour in bases and acids,but extracted naturally.
Example: Turmeric, Litmus, China rose Salt + CO2(g) + H2O No Reaction
(i) Litmus Paper: For Acids: Blue litmus paper changes e.g., 2HCl + Na2CO3 → 2NaCl + CO2(g) + H2O
colour to red in acids. HCl + NaHCO3 → NaCl + CO2(g) + H2O
For Bases: Red litmus paper changes colour to blue in Test for CO2: CO2 can be tested by passing it through
bases. lime water. Lime water turns milky due to formation of
(ii) China Rose: For Acids: It changes colour to red in insoluble calcium carbonate (white precipitate).
acids. Ca(OH)2 + CO2 → CaCO3 + H2O
, 4 | Oswaal CBSE Question Bank | SCIENCE | Class 10
When excess CO2 is passed, milkiness disappears due to • Similarly, substances which when dissolved in water
formation of soluble calcium hydrogen-carbonate. ionise to produce hydroxide ions, OH– (aq).
CaCO3 + CO2 + H2O → Ca(HCO3)2 Examples: When sodium hydroxide is dissolved in water, it
3. Reaction of Acids and Bases with Each Other dissociates into hydroxide and sodium ion.
When an acid reacts with base, the hydrogen ion of acid
combines with hydroxide ion of base and forms water. As NaOH(s) Na+(aq) + OH– (aq)
these ions combine together, they form water instead of 4. Reaction of Acids with Metal Oxides:
remaining free, thus both neutralise each other. Metal oxides react with acids to give salt and water.
Acid + Base → Salt + Water [Board 2024] Metal oxide + Acid → Salt + Water
Since in the reaction between an acid and Properties of Example: Copper oxide reacts with dilute hydrochloric acid
a base both neutralise each other, it is also Acids and Bases to form copper chloride (salt) and water.
known as neutralisation reaction.
Example: Sodium hydroxide (a strong CuO + 2HCl(dil.) → CuCl2 + H2O
base) reacts with hydrochloric acid to form Copper oxide Copper chloride
sodium chloride and water. Copper oxide is black in colour. When dilute hydrochloric
NaOH(aq) + HCl(aq) → NaCl(aq) + acid is added to it, the colour of the solution becomes blue-
Scan Me!
H2O(l) green due to the formation of copper chloride.
4. Reaction of Metallic Oxides with Acids: How Strong Are Acid or Base Solutions?
When metallic oxides react with acids, formation of salt
and water takes place. • Strength of an acid or base depends on the number of
Metal Oxide + Acid → Salt + Water H+ ions or OH– ions produced by them respectively.
For Example: Copper oxide reacts with hydrochloric • Based on its ability to dissociate into ions in the solution,
acid, formation of copper chloride and water take place acids and bases are classified as strong acid or base and
CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l) weak acid or base.
5. Reaction of Non-Metallic Oxides with Basess: (a) Strong Acids: Acids that completely dissociate in
When non-metallic oxides react with bases, formation of water to produce large amount of hydrogen ions are
salt and water takes place. called strong acids. For example, hydrochloric acid
Non-Metal Oxide + Base → Salt + Water (HCl), sulphuric acid (H2SO4), nitric acid (HNO3) are
For Example: Carbon dioxide reacts with calcium strong acids as they get completely ionised in water to
hydroxide, formation of calcium carbonate and water form ions.
take place
HCl (aq) → H+(aq) + Cl– (aq)
Ca(OH)2(s) + CO2(aq) + → CaCO3(s) + H2O(l)
Common Properties of All Acids and Bases [Board 2024] (b) Weak Acids: Acids which get partially ionised in
water to produce small amount of hydrogen ions are
• Acids give hydrogen gas when they react with metal. known as weak acids. For example, acetic acid partially
This shows that all acids contain hydrogen. dissociates in water to produce small amount of
• When acids are dissolved in water they dissociate as hydrogen ions.
H+ ions. The dissociation of hydrogen ions in aqueous CH3COOH (aq) → H+ (aq) + CH3COO–(aq)
solution is the common property of all acids. As a result,
(c) Strong Bases: Bases which completely ionise in
an acid shows acidic behaviour.
water to produce large amount of hydroxide ions are
HCl (aq) → H+(aq) + Cl– (aq)
called strong bases. Examples include NaOH, KOH, etc.
HNO3(aq) → H+(aq) + NO3– (aq)
(d) Weak Bases: Bases which partially pH Scale
CH3COOH (aq) → H+ (aq) + CH3COO– (aq) dissociate in water to furnish lesser
• As H+ ion cannot exist alone, it combines with water amount of hydroxide ions are called
molecules and forms H3O+ (hydronium) ions. weak bases. Examples include
Example: ammonium hydroxide (NH4OH) and
HCl + H2O → H3O+ + Cl– calcium hydroxide Ca(OH)2.
Scan Me!
H+ + H2O → H3O+ pH
The concentration of H+ is generally
Thus, acids can also be defined as substances, which when small, therefore concentrations of H+ pH: A scale for measu
ring
dissolved in water ionise to produce hydrogen ions, H+ (aq). is expressed in terms of pH. H+ ion con cen tra tio n in
a solution..
Key Diagram
