ICSE Class 8 Chemistry Sample Paper with Solutions Set 01

Question 1
Choose the correct answer out of the four available choices given under each question. [15]

1. The phenomenon of existence of a substance in various physical forms but the same chemical form is known as _________. [1 Mark]
(a) Catenation
(b) Isomerism
(c) Polymerisation
(d) Allotropy

Answer: (d) Allotropy

The phenomenon due to which an element can exist in more than one structural form in the same physical state is called allotropy.

Teacher's Note:
a) Allotropy is exhibited by non-metals like carbon, sulphur, and phosphorus.
b) Do not confuse allotropy with isomerism, which applies to compounds having the same molecular formula but different structures.

2. Alkali metals such as __________ and ___________ are soft metals and can be cut easily with a knife. [1 Mark]
(a) Lithium, aluminium
(b) Calcium, lithium
(c) Sodium, potassium
(d) Lead, zinc

Answer: (c) Sodium, potassium

Alkali metals such as sodium and potassium have weak metallic bonding due to a single valence electron, making them extremely soft.

Teacher's Note:
a) Alkali metals belong to Group 1 of the periodic table.
b) Lithium is also a soft alkali metal, but among the given options, sodium and potassium form the correct pair typically highlighted in textbooks.

3. Carbon has __________ unpaired electron(s) in its outermost shell. [1 Mark]
(a) Four
(b) One
(c) Three
(d) Six

Answer: (a) Four

Carbon has an atomic number of 6 with an electronic configuration of 2, 4, having four valence electrons which remain unpaired in its ground state.

Teacher's Note:
a) These four valence electrons allow carbon to exhibit tetravalency.
b) Carbon achieves a stable octet by sharing these four electrons through covalent bonding.

4. Which of the following is not a mixture? [1 Mark]
(a) Sulphur
(b) Gunpowder
(c) Sugar syrup
(d) Milk

Answer: (a) Sulphur

Sulphur is a pure chemical element, whereas gunpowder, sugar syrup, and milk are mixtures.

Teacher's Note:
a) An element consists of only one type of atom.
b) Mixtures are composed of two or more substances physically combined in no fixed proportion.

5. Liquids have [1 Mark]
(a) less compressibility than solids
(b) more compressibility than gases
(c) more compressibility than solids
(d) the least compressibility among the three states of matter

Answer: (c) more compressibility than solids

The intermolecular space between the particles of liquids is more than that of solids, allowing particles to slip and slide, rendering liquids more compressible than solids.

Teacher's Note:
a) Gases have the highest compressibility, followed by liquids, while solids have the least compressibility.
b) Read all options carefully before answering, as options (a) and (c) state opposite comparisons.

6. Which of the following gases dissolves in rainwater and forms nitric acid? [1 Mark]
(a) Nitrogen dioxide
(b) Nitrogen trioxide
(c) Ammonia
(d) Nitride

Answer: (a) Nitrogen dioxide

Nitrogen dioxide dissolves in rainwater in the presence of oxygen to form nitric acid, contributing to acid rain.

Teacher's Note:
a) Nitrogen dioxide is primarily released from vehicle exhausts and industrial emissions.
b) This reaction is a key component of atmospheric chemistry related to pollution.

7. When the temperature of water increases above 0°C up to 4°C, its density [1 Mark]
(a) decreases
(b) increases
(c) becomes zero
(d) remains unchanged

Answer: (b) increases

Water exhibits anomalous expansion; when heated from 0°C to 4°C, it contracts, leading to an increase in density up to a maximum at 4°C.

Teacher's Note:
a) The maximum density of water is 1 g/cm³ at 4°C.
b) This unique property helps aquatic life survive in cold climates as ice floats on top.

8. When an electric current is passed through acidulated water, _________ volume of hydrogen is formed at the cathode and __________ volume of oxygen is formed at the anode. [1 Mark]
(a) one, two
(b) one, three
(c) three, one
(d) two, one

Answer: (d) two, one

During the electrolysis of acidulated water, two volumes of hydrogen gas are collected at the cathode for every one volume of oxygen gas collected at the anode.

Teacher's Note:
a) This ratio reflects the chemical formula of water, H₂O.
b) Remember that hydrogen forms at the cathode (negative electrode) and oxygen at the anode (positive electrode).

9. ___________ is the process of sterilisation of water by the addition of chlorine and acts as a treatment against bacterial infection. [1 Mark]
(a) Chlorination
(b) Precipitation
(c) Sedimentation
(d) Decantation

Answer: (a) Chlorination

Chlorination is the process of sterilising water by adding chlorine to kill harmful bacteria and microorganisms.

Teacher's Note:
a) Chlorination is an essential step in municipal water treatment plants.
b) Sedimentation and decantation remove suspended impurities, whereas chlorination specifically targets pathogens.

10. The valency of Cu in cupric chloride is. [1 Mark]
(a) 1
(b) 2
(c) 3
(d) 4

Answer: (b) 2

In cupric chloride (CuCl₂), copper exhibits its higher valency of 2, denoted by the suffix -ic.

Teacher's Note:
a) Cuprous compounds have copper with a valency of 1 (e.g., CuCl).

b) Cupric compounds have copper with a valency of 2 (e.g., CuCl₂).

11. The formation of gas bubbles in a liquid during a reaction is called [1 Mark]
(a) Precipitate
(b) Effervescences
(c) Fumes
(d) Vapours

Answer: (b) Effervescences

Effervescence refers to the escape of gas from an aqueous solution resulting in the formation of bubbles during a chemical reaction.

Teacher's Note:
a) A precipitate is an insoluble solid formed in a solution during a chemical reaction.
b) Effervescence is commonly observed when an acid reacts with a metal carbonate.

12. The phenomenon of the existence of a substance in various physical forms but the same chemical form is known as [1 Mark]
(a) Catenation
(b) Isomerism
(c) Polymerisation
(d) Allotropy

Answer: (d) Allotropy

Allotropy is the property of an element to exist in two or more different physical forms in the same physical state.

Teacher's Note:
a) This is a repeated question reinforcing the definition of allotropy.
b) Diamond and graphite are classic allotropes of carbon.

13. Graphite is made of layers of crystals, where each crystal is __________. [1 Mark]
(a) Tetrahedral cubical
(b) Cubical
(c) Hexagonal
(d) Spherical

Answer: (c) Hexagonal

In graphite, each carbon atom is bonded to three other carbon atoms in the same plane, forming repeating hexagonal rings arranged in layers.

Teacher's Note:
a) The layered structure held by weak van der Waals forces makes graphite soft and slippery.
b) Contrast this with diamond, which has a rigid tetrahedral 3D network structure.

14. Which element has symbol derived from its Latin name Argentum? [1 Mark]
(a) Gold
(b) Silver
(c) Aluminium
(d) Argon

Answer: (b) Silver

The chemical symbol for silver is Ag, which is derived from its Latin name argentum.

Teacher's Note:
a) Many elements have symbols derived from Latin, Greek, or German names.
b) For example, gold is derived from aurum (Au), and sodium from natrium (Na).

15. Which of the following substances are bitter to taste? [1 Mark]
(a) Baking soda
(b) Lemons
(c) Oranges
(d) Tamarind

Answer: (a) Baking soda

Baking soda is basic in nature, and bases are typically bitter to taste and soapy to touch.

Teacher's Note:
a) Lemons, oranges, and tamarind contain organic acids and are sour to taste.
b) Acids turn blue litmus red, whereas bases turn red litmus blue.

Question 2

(A) Give the molecular formula of the compounds: [5 Marks]
1. Common salt
2. Sand
3. Marble
4. Acetic acid
5. Aluminium oxide

Answer:
1. Sodium chloride: NaCl
2. Silicon dioxide: SiO₂
3. Calcium carbonate: CaCO₃
4. Acetic acid: CH₃COOH
5. Aluminium oxide: Al₂O₃

Teacher's Note:
a) Students must learn correct chemical formulas and valencies of radicals to write compound formulas accurately.
b) Subscripts indicate the number of atoms of each element in the molecule.

(B) Fill in the blanks and rewrite the sentences: [5 Marks]
1. The unique ability of the carbon atom to combine with innumerable carbon atoms and atoms of other elements resulting in the formation of millions of organic compounds is called _________.
2. Alkalis are bases which are _________ in water.
3. If the outermost shell of an atom is filled, the valency is ________.
4. Metals are __________ because metals readily __________ electrons and form positively charged ions.
5. Hydrogen can be prepared in the laboratory by the reaction of zinc and __________.

Answer:
1. catenation
2. soluble
3. zero
4. electropositive, lose
5. dilute sulphuric acid (or dilute hydrochloric acid)

Teacher's Note:
a) Catenation is the self-linking property of carbon responsible for vast organic diversity.
b) Inert gases have completely filled outermost shells, hence their valency is zero.

Question 3

(A) State whether the following statements are true or false. Rewrite the false statement. [5 Marks]
1. Lignite is the third stage in the formation of coal.
2. Balanced chemical equation shows both the number of molecules and the number of atoms involved in the reaction.
3. Dehydration of carbohydrates is a physical change.
4. The mass of a proton is equal to that of a neutron.
5. Positively charged ions are called cations.

Answer:
1. False. Bituminous is the third stage in the formation of coal (or Lignite is the second stage).
2. True.
3. False. Dehydration of carbohydrates is a chemical change.
4. True.
5. True.

Teacher's Note:
a) Coal formation stages in order of carbon content are peat, lignite, bituminous, and anthracite.
b) Dehydration involves a change in chemical composition, making it a chemical change.

(B) Name the following: [5 Marks]
1. The subatomic particle with negative charge and negligible mass.
2. Protons and neutrons present in the nucleus.
3. The electrons present in the outermost shell.
4. The number of protons present in the nucleus of an atom.
5. Atoms of the same element with the same atomic number but different mass number.

Answer:
1. Electron
2. Nucleons (or Protons and neutrons)
3. Valence electrons
4. Atomic number
5. Isotopes

Teacher's Note:
a) Ensure precise scientific terms are used for each definition.
b) Nucleons is the collective term for particles residing inside the nucleus.

Question 4

(A) Explain Modern Atomic Theory... [5 Marks]

Answer:
According to the modern, standard model of atom:
1. An atom comprises three fundamental particles: electrons, protons, and neutrons.
2. There are two structural parts of an atom: (i) The nucleus, and (ii) The orbits or shells in the surrounding space.
3. The nucleus is the positively charged, central part of an atom containing protons and neutrons, collectively known as nucleons.
4. Nucleons are held firmly in the nucleus by strong nuclear forces.
5. The entire mass of an atom lies in its nucleus, since electrons have negligible mass.
6. The positive charge of the nucleus is due to the protons present in it.
7. Orbits or shells are the imaginary paths traced by electrons in the empty space surrounding the nucleus.
8. Each orbit is associated with a fixed amount of energy.
9. Electrically neutral atoms contain an equal number of protons and electrons.

Teacher's Note:
a) Emphasize the dual structure of the atom comprising the nucleus and extranuclear orbits.
b) Mentioning subatomic particle masses and charges clarifies the atomic model.

(B) Explain catalyst and their actions? [5 Marks]

Answer:
1. A catalyst is a substance which either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the process.
2. Positive Catalyst: When a catalyst increases the rate of a reaction, it is known as a positive catalyst. For example, manganese dioxide (MnO₂) acts as a positive catalyst in the thermal decomposition of potassium chlorate.
\( 2KClO_3 \xrightarrow[\text{300}^{\circ}\text{C}]{\text{MnO}_2} 2KCl + 3O_2 \uparrow \)
3. Negative Catalyst: When a catalyst decreases the rate of a reaction, it is known as a negative catalyst. For example, phosphoric acid acts as a negative catalyst to decrease the rate of decomposition of hydrogen peroxide.

Teacher's Note:
a) Catalysts alter reaction rates by providing an alternative pathway with a different activation energy.
b) Ensure balanced chemical equations with proper catalyst notations are written where applicable.

Question 5

(A) Draw the orbital diagrams representing the atomic structures of the following: [5 Marks]
1. Silicon
2. Neon
3. Copper
4. Calcium
5. Sodium

Answer:
1. Silicon (Atomic Number 14, Configuration: 2, 8, 4): Central nucleus labeled 'Si' surrounded by three concentric shells with 2, 8, and 4 electrons respectively.
2. Neon (Atomic Number 10, Configuration: 2, 8): Central nucleus labeled 'Ne' surrounded by two concentric shells with 2 and 8 electrons respectively.
3. Copper (Atomic Number 29, Configuration: 2, 8, 18, 1): Central nucleus labeled 'Cu' surrounded by four concentric shells with 2, 8, 18, and 1 electrons respectively.
4. Calcium (Atomic Number 20, Configuration: 2, 8, 8, 2): Central nucleus labeled 'Ca' surrounded by four concentric shells with 2, 8, 8, and 2 electrons respectively.
5. Sodium (Atomic Number 11, Configuration: 2, 8, 1): Central nucleus labeled 'Na' surrounded by three concentric shells with 2, 8, and 1 electrons respectively.

[Figure: Schematic Bohr atomic models showing shells with electron dots for Silicon, Neon, Copper, Calcium, and Sodium as described above.]

Teacher's Note:
a) Students must correctly distribute electrons into shells according to the 2n² rule while keeping outermost shell capacities in mind.
b) Clear labeling of the nucleus and distinct electron dots on circular orbits are essential for full credit.

(B) Give one use of each of the following acids: [5 Marks]
1. Citric acid
2. Acetic acid
3. Tartaric acid
4. Boric acid
5. Carbonic acid

Answer:
1. Citric acid: Used in food preservation and vitamin C preparation.
2. Acetic acid: Used as table vinegar and for cooking food.
3. Tartaric acid: Used in the manufacture of baking powder.
4. Boric acid: Used as a mild antiseptic and eye wash.
5. Carbonic acid: Used in the manufacture of flavoured carbonated drinks.

Teacher's Note:
a) Organic and inorganic acids have diverse domestic and industrial applications.
b) Precise industrial or domestic uses should be mentioned concisely.

Question 6

(A) Define the following terms: [5 Marks]
1. Chemical bond
2. Valency
3. Boiling point
4. Radicals
5. Mass number

Answer:
1. Chemical Bond: The attractive force which holds two or more atoms of a molecule together in a compound.
2. Valency: The combining capacity of an element. (Note: When an element exhibits more than one valency in different compounds, the property is called variable valency).
3. Boiling point: The constant temperature at which a liquid becomes a gas upon absorbing heat under normal atmospheric pressure.
4. Radicals: A group of atoms of elements that act as a single unit with a positive or negative charge in chemical reactions.
5. Mass number: The total sum of the number of protons and the number of neutrons present in the nucleus of an atom of an element, denoted by 'A'.

Teacher's Note:
a) Definitions must include key scientific keywords such as attractive force, combining capacity, and sum of nucleons.
b) Providing examples alongside definitions enhances clarity.

(B) Match the column: [5 Marks]

Answer:
Corrected pairings based on standard chemical ions:
1. Ammonium - NH₄⁺
2. Nitrite - NO₂^-
3. Aluminium - Al³⁺
4. Carbonate - CO₃^2-

Teacher's Note:
a) The original question paper table contained misaligned symbols (e.g., Al³⁺ against Ammonium). The matched table above provides the scientifically correct pairings.
b) Students must learn formula charges of common radicals thoroughly.

Question 7

(A)
1. How can you prove that hydrogen burns in air to produce water? [3 Marks]

Answer:
1. Hydrogen, produced by the action of dilute sulphuric acid on zinc, is passed through anhydrous calcium chloride (for drying) and then lighted at the end of a jet.
2. Pure, dry hydrogen burns with a pale blue flame and produces water droplets which condense on the cold inner surface of a dry inverted flask kept over the flame.
3. The condensed liquid can be tested by adding a few drops onto white anhydrous copper sulphate; the white powder turns blue, proving the liquid is water.

Teacher's Note:
a) This experiment demonstrates the synthesis (combination) reaction of hydrogen and oxygen.
b) Mentioning the anhydrous copper sulphate color change is crucial for confirming the presence of water.

2. Differentiate between oxidation reaction and reduction reaction. [2 Marks]

Answer:

Teacher's Note:
a) Oxidation and reduction always occur simultaneously in a redox reaction.
b) Tabular comparisons should clearly list corresponding opposite processes.

(B)
1. Give reason: Although hydrogen is lighter than air, it is not collected by the downward displacement of air. [2 Marks]

Answer:
Although hydrogen is much lighter than air, it is not collected by downward displacement of air because hydrogen mixes with air to form a highly explosive mixture when exposed to a spark or flame.

Teacher's Note:
a) Safety is paramount when handling hydrogen gas due to its extreme flammability.
b) Hydrogen is instead collected by downward displacement of water because it is insoluble in water.

2. What are protons, neutrons and electrons? [3 Marks]

Answer:
1. Protons: Positively charged particles (+1 charge) found in the nucleus of an atom, having a unit mass of approximately 1 atomic mass unit.
2. Neutrons: Neutral particles with zero electrical charge found in the nucleus of an atom, having a unit mass of approximately 1 atomic mass unit.
3. Electrons: Negatively charged particles (-1 charge) revolving in orbits outside the nucleus of an atom, having a negligible mass.

Teacher's Note:
a) These three particles constitute the fundamental subatomic building blocks of all atoms.
b) Clear mention of charge, mass, and location for each particle secures full marks.