Science Revised syllabus for class 10th
CHAPTER 1
CHEMICAL REACTIONS AND EQUATIONS
Syllabus for 2020-21 :
Chemical equation, Balanced chemical equation, implications of
a balanced chemical equation, types of chemical reactions: combination,
decomposition, displacement, double displacement, precipitation, neutralization, oxidation and reduction.
TYPES OF CHEMICAL REACTIONS : (3)
1. COMBINATION REACTION
A reaction in which two or more reactants combine to form a single product is called a combination
reaction.
E.g. C + O2 → CO2
2. DECOMPOSITION REACTION
A reaction in which a compound splits into two or more simple substances is called a decomposition reaction.
a) Thermal decomposition : When decomposition is carried out by heating.
E.g. CaCO3 → CaO + CO2
b) Electrolytic decomposition : When decomposition is carried out by passing electricity.
E.g. 2H2O → 2H2 + O2
c) Photolytic decomposition : When decomposition is carried out in presence of sunlight.
E.g. 2AgCl → 2Ag +Cl2
White coloured silver chloride turns grey on exposure to sunlight.
This reaction is used in black and white photography.
3. DISPLACEMENT REACTION
The chemical reaction in which a more reactive element displaces a less reactive element from its salt
solution is called displacement reaction.
E.g. Fe + CuSO4 → FeSO4 + Cu
The blue colour of copper sulphate changes to pale green colour due to the formation of ferrous sulphate
and brown coloured deposition of copper is observed.
4. DOUBLE DISPLACEMENT REACTION
A reaction in which new compounds are formed by mutual exchange of ions between the reactants is called
double displacement reaction.
E.g. Na2SO4 + BaCl2 → BaSO4 + 2NaCl
White precipitate of barium sulphate is formed, so it is also called a precipitation reaction.
5. OXIDATION AND REDUCTION/REDOX REACTION (2)
Oxidation : Addition of oxygen to reactant / Removal of hydrogen from a reactant.
C + O2 → CO2
Reduction : Addition of hydrogen to reactant/ Removal of oxygen from reactant.
CuO + H2 → Cu + H2O
In this reaction, substance oxidized is H2 and substance reduced is CuO.
CuO is oxidizing agent and H2 is reducing agent.
Since oxidation and reduction are taking place together, it is a redox reaction.
QUESTIONS
1. Give reason why
a) Iron displaces copper from copper sulphate solution.
b) We store silver chloride in dark coloured bottles in labs. (2)
2. A small amount of Ferrous sulphate is heated in hard glass tube.
a) Write the balanced chemical reaction involved.
b) Name the type of reaction taking place. (2)
3. (a) Identify (i) the reducing and oxidizing agents (ii) substance getting oxidized and reduced in the
given chemical reaction : CuO + H2 → Cu + H2O
(b) Give an example of a double displacement reaction.
CHAPTER 2
ACIDS BASES AND SALTS
Syllabus for 2020-21 : Acids, bases and salts: Their definitions in terms of furnishing of H+ and OH– ions, General properties, examples and uses, concept of pH scale (Definition
relating to logarithm not required), importance of pH in everyday life; preparation and uses of Sodium Hydroxide, Bleaching powder, Baking soda, Washing soda and Plaster of Paris.
ACIDS AND BASES (2)
ACIDS
• Sour in taste
• Turn blue litmus red
• Release hydrogen (hydronium) ions
[H+(aq) or H3O+] in water/ aqueous
solutions
• Conduct electricity in aqueous
solution
Examples:
• Sulphuric acid - H2SO4
• Hydrochloric acid - HCl
• Acetic Acid - CH3COOH
• Nitric Acid - HNO3
BASES
• Bitter in taste, have soapy touch
• Turn red litmus blue
• Release hydroxide ions (OH–) in
water/ aqueous solutions
• Conduct electricity in aqueous
solution
Examples:
• Sodium hydroxide (caustic soda) –
NaOH
• Calcium hydroxide – Ca(OH)2
• Potassium hydroxide (caustic
potash)– (KOH)
Alkalis are bases soluble in water.
Some naturally occurring acids:
Substance Acid Present
Vinegar Acetic acid
Curd Lactic acid
Tamarind Tartaric acid
Spinach Oxalic acid
PREPARATION OF SODIUM HYDROXIDE (NaOH): (1)
NaOH is obtained by the electrolytic decomposition of solution of sodium chloride. This whole process is
known as Chlor-Alkali process. Cl2 and H2 are other by-products of this process.
2NaCl (aq) + 2H2O (l) → 2NaOH (aq) + Cl2 (g) [Anode] + H2 (g) [Cathode]
ACID-BASE INDICATORS : (2)
Indicators are substances or chemicals that help us to identify whether the given solutions are acids or bases.
pH SCALE : (2)
• Range = 0 to 14
• Neutral substance has the pH of exactly 7
• Acidic substance has the pH less than 7
• Basic substance has the pH more than 7
Importance of pH In Everyday Life :
1. pH in our digestive system: When our stomach produces excess acid, it causes indigestion. In order
to cure indigestion we take a mild base like baking soda [NaHCO3] or milk of magnesia [Mg(OH)2].
These are known as ‘Antacids‘. They neutralize the excess acid and give relief.
2. pH change as the cause of tooth decay: Tooth decay starts when the pH of mouth falls below 5.5.
The best way to prevent tooth decay is to clean the mouth after eating and using a basic toothpaste
which can neutralize acid inside mouth.
3. Self Defense by animals and plants through chemical warfare: Ant sting or nettle sting injects
methanoic acid into a person’s body. Its sting causes pain and irritation. Baking soda is used as a
remedy because being a base it neutralizes the injected acid.
4. pH in soil: If the soil is too acidic then it is treated with materials like quicklime (CaO) or slaked
lime. If the soil is too alkaline then alkalinity can be reduced by adding decaying organic matter.
SALTS (3)
Salts are the ionic compounds which are produced after the neutralization reaction between acids and bases.
BAKING SODA
Chemical name – Sodium hydrogen carbonate Formula – NaHCO3
Preparation–
a). By heating Limestone : CaCO3 → CaO + CO2
b). CO2 is passed through a concentrated solution of sodium
chloride and ammonia:
NaCl(aq)+NH3(g)+CO2(g)+H2O(l)→NaHCO3(aq)+NH4Cl(aq)
Uses:
1. In Textile industry
2. In Paper industry
3. As Disinfectant
Baking Powder
❖ Baking Powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid.
WASHING SODA
Chemical name – Sodium Carbonate Formula – Na2CO3.10 H2O
Preparation–
Na2CO3 + 10 H2O → Na2CO3.10 H2O
Uses:
1. In Glass, Soap and Paper
industries
2. For softening of water
3. As Domestic cleaner
BLEACHING POWDER
Chemical name – Calcium Oxychloride Formula – CaOCl2
Preparation–
Ca(OH)2(aq) + Cl2(g)→ CaOCl2(aq) + H2O(l)
On interaction with water – bleaching powder releases chlorine which is responsible for bleaching action.
PLASTER OF PARIS (POP)
Chemical name – Calcium Sulphate Hemi Hydrate Formula – CaSO4. ½ H2O
Preparation–
Gypsum, CaSO4.2H2O (s) on heating at 100°C (373K) gives CaSO4. ½ H2O and 3/2 H2O
CaSO4. ½ H2O is Plaster of Paris.
Water of crystallization
Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.
Examples: CuSO4. 5H2O
CaSO4 .2H2O
Na2 CO3 .10H2O
FeSO4.7H2O
QUESTIONS
1. What is the colour of Methyl Orange in a basic medium? (1)
2. Mention the two constituents of Baking Powder? Give its uses (any two). (2)
3. What is the chemical name of POP? What happens when water is added to it? Write the balanced
chemical reaction for it. (2)
4. Define water of crystallization. Give examples of two salts that have water of crystallization and also
write their chemical formulae.
CHAPTER 3
METALS AND NON-METALS
Syllabus for 2020-21 : Properties of metals and non-metals; Reactivity series; Formation and properties of ionic compounds
Deletion for 2020-21 : Basic metallurgical processes; Corrosion and its prevention
EXCEPTIONS IN METALS AND NON-METALS :
(2)
NATURE OF OXIDES :
REACTIVITY SERIES : (2)
The reactivity series is a list of metals arranged in the order of their decreasing activities.
Reactivity series has been developed by performing displacement reactions.
* Metal which is liquid at room temperature MERCURY
* Metals with very low melting
points that may melt on our palm
GALLIUM AND CAESIUM
* Metals which are soft and can be cut with a knife; have low densities and low melting points LITHIUM, SODIUM, POTASSIUM
* Non-metal which is lustrous IODINE
* Non-metal which is a good conductor of electricity GRAPHITE (ALLOTROPE OF CARBON)
* Non-metal which has a very high
melting and boiling point DIAMOND (ALLOTROPE OF CARBON)
Metal oxides –BASIC
Non-metal oxides –ACIDIC
Chemical Properties of Metals : (2)
Metal + Oxygen → Metal oxide
Metal + Water → Metal oxide +
Hydrogen
Metal + Dilute Acid → Salt + Hydrogen
(Note : All metals do not react in the
same manner.)
Amphoteric oxides : (2)
Metal oxides which react with both acids as well as bases to produce salts and water are known as
amphoteric oxides.
E.g. Aluminium oxide (Al2O3), Zinc oxide (ZnO)
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Al2O3 + 2NaOH → 2NaAlO2 + H2O
A more reactive metal (A) displaces a less reactive metal (B) from its salt solution.
Metal A + Salt solution of B → Salt solution of A + Metal B
e.g. Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
Some metals arranged in decreasing order of activity : Al > Zn > Fe > Cu
IONIC COMPOUNDS : (2)
Compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds (or electrovalent compounds).
Sodium Chloride (NaCl)
Magnesium Chloride (MgCl2)
Ionic compound formation :
Properties of ionic compounds : (2)
1. Solid and hard (due to strong force of attraction between ions)
2. High melting and boiling points (due to high amount of energy to break strong inter-ionic attraction)
3. Generally soluble in water (by dissociation of ions)
4. Conduct electricity in molten state and in aqueous solution (due to free movement of ions)
QUESTIONS
1. Name
(i) a metal which can be easily cut with a knife
(ii) a non-metal which is a good conductor of electricity. (1)
2.(a) Oxide of an element ‘X’ was found to convert red litmus to blue.
What does this tell about the nature of the oxide? Is ‘X’ a metal or a non-metal?
(b)What happens when Zinc granules are added to dilute Sulphuric acid?
(c) Why are ionic compounds good conductors of electricity? (3)
3. (a) What do you understand by reactivity series?
(b) Arrange Fe, Zn, Cu and Al in decreasing order of activity? Which is most reactive among them? (3)
CHAPTER 4
CARBON AND ITS COMPOUNDS
Syllabus for 2020-21 : Covalent bonding in carbon compounds. Versatile nature of carbon. Homologous series
Deletion for 2020-21 : Nomenclature of carbon compounds containing functional groups (halogens, alcohol, ketones, aldehydes, alkanes and alkynes), difference between saturated hydrocarbons and unsaturated hydrocarbons, Chemical properties of carbon compounds (combustion, oxidation, addition and substitution reaction), Ethanol and Ethanoic acid (only properties and uses), soaps and detergents
* Bonds which are formed by the sharing of an electron pair between two atoms are known as covalent
bonds.
VERSATILE NATURE OF CARBON (2)
(i) CATENATION : Carbon can link with carbon atoms by means of covalent bonds to form long chains,
branched chains and closed ring compounds. Carbon atoms may be linked by single, double or triple bonds.
(ii) TETRAVALENCY : Carbon has 4 valence electrons. Carbon can bond with 4 other carbon atoms, mono-
valent atoms, oxygen, nitrogen and sulphur.
Carbon is tetravalent, it does not form ionic bond by either losing 4 electrons or by gaining 4 electrons. So, Carbon can form bond only by sharing of electrons and hence forms only covalent compounds.
Properties of Covalent compounds : (1)
* Have low melting and boiling points as they have weak intermolecular forces
* Are generally poor conductors of electricity as there is sharing of electrons and no ions are formed.
Compounds made up of hydrogen and carbon only are called hydrocarbons. E.g. CH4
ALLOTROPES OF CARBON (2)
GRAPHITE
* Hexagonal arrays placed in layers one above the other ( 2-Dimensional structure)
* Each carbon atom bonded to three other carbon atoms, one of the bonds being double bond
*Smooth and slippery
*Good conductor
*Uses - lubricant, pencil DIAMOND
*Rigid 3-Dimensional structure
*Each carbon atom bonded to four other carbon atoms
*Hardest known substance
*Bad conductor
*Uses - cutting tools, jewellery
HOMOLOGOUS SERIES (2)
A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is
called a homologous series.
E.g., Alkanes - CH4, C2H6, C3H8, C4H10
Characteristics of a Homologous Series
*Have same general formula
*Differ by a -CH2 group
*Difference in molecular formula is 14u
*Show regular gradation in physical properties but have same chemical properties
STRUCTURAL ISOMERISM (3)
Compounds with identical molecular formula but different structures are called structural isomers.
The two structural isomers of Butane with molecular formula C4H10 are
The three structural isomers of Pentane with molecular formula C5H12 are
QUESTIONS
1. Why does carbon atom form a large number of compounds? (1)
2. Which of the following is a good conductor of electricity - Diamond or Graphite? Why?(2)
3. What is structural isomerism? Draw the structural isomers of Butane and Pentane. (3)
4. What is a homologous series? Explain with the help of an example. (3)
5. C3H6, C4H8, C5H10 belong to the same homologous series. Arrange these hydrocarbons in order of
increasing boiling points. Give reason also. (2)
CHAPTER 5
PERIODIC CLASSIFICATION OF ELEMENTS
Syllabus for 2020-21 : Need for classification, early attempts at classification of elements (Dobereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table), Modern periodic table, gradation in properties, valency, atomic size, metallic and non-
metallic properties
DOBEREINER’S TRIADS : When three elements are written in the order of increasing atomic masses, the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements. E.g. Li, Na, K
MENDELEEV’S PERIODIC LAW : The properties of elements are a periodic function of their atomic masses.
THE MODERN PERIODIC LAW : The properties of elements are a periodic function of their atomic number.
ACHIEVEMENTS OF MENDELEEV’S PERIODIC TABLE :
1. Mendeleev sometimes placed an element with a slightly greater atomic mass before an element
with a slightly lower atomic mass. The sequence was inverted so that elements with similar properties could be grouped together. Eg. Cobalt (atomic mass 58.9) appeared before Nickel (atomic mass 58.7).
2. Mendeleev left some gaps in his periodic table and boldly predicted the existence of some elements that had not been discovered at that time. E.g. Scandium, Gallium and Germanium discovered later have properties similar to the elements predicted by Mendeleev as Eka-Boron, Eka-Aluminium and Eka-Silicon respectively.
3. One of the strengths of Mendeleev’s periodic table was that when noble gases were discovered,
they could be placed in a new group without disturbing the existing order.
LIMITATIONS OF MENDELEEV’S CLASSIFICATION :
1. No fixed and correct position can be given to hydrogen.
2. Isotopes of all elements posed a challenge to Mendeleev’s periodic law.
3. Atomic masses do not increase in a regular manner in going from one element to the next. So it was not possible to predict how many elements could be discovered between two elements, especially when we consider the heavier elements.
How does the Modern Periodic Table take care of three limitations of Mendeleev’sPeriodic Table?
1. Hydrogen was given correct position.
2. The atomic number of each element is unique. So isotopes did not create any kind of challenge as all isotopes of the same element have same atomic no.
3. The atomic number increases by one in going from one element to the next.
It could be easily ascertained as to how many elements would be found in between two given elements.
Identifying group and period based on atomic number in Modern
Periodic Table :
Step-1 : Write electronic configuration on the basis of atomic number.
Step-2 : Look at the no. of electrons present in the valence shell (outermost shell).
It helps us to find group number.
Step-3 : Count the number of shells. It helps us to find the period number.
TRENDS IN PROPERTIES IN MODERN PERIODIC TABLE :
1. Atomic size or atomic radii
Down the group – INCREASES (due to increase in no. of shells)
Across the period – DECREASES (due to increase in effective nuclear charge)
2. Valency
Across the period – FIRST INCREASES AND THEN DECREASES
Down the group –INCREASES
3. Metallic character (electropositive nature /tendency to lose electron)
Across the period - DECREASES
Down the group – REMAINS SAME
4. Non-metallic character (electronegative nature/tendency to gain electron)
Down the group – DECREASES
Across the period - INCREASES
QUESTIONS
1. Mention three limitations of Mendeleev’s Periodic Table. How did the Modern Periodic Table take care of these limitations? (3)
2. An element P has electronic configuration 2,8,5. In which group and period will it be placed? Another element Q has electronic configuration 2,5. Can it be placed in same group and period as element P? (2)
3. What trends are observed in atomic size in Modern Periodic Table when we move (i) down the group ? (ii) across the period? Why? (3)
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