Chemistry test paper for students of class 7 of ICSE Board. This test paper includes two chapter of the chemistry which will be helpful to the students of class 7.
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Chemistry test (2023 - 24)
Class 7 (ICSE Board)
Chapters:
Total marks:
Total time:
(A) Choose the correct answers: (1 marks each)
1. Which of the following techniques is used to separate components of mixture of miscible liquids?
(a) Evaporation
(b) Fractional distillation
(c) Sublimation
(d) Filtration
2. Which of the following method is used by gulf countries to get drinking water from seawater?
(a) Distillation
(b) Filtration
(c) Sublimation
(d) Chromatography
3. Which of the following is electrically neutral?
(i) Electron
(ii) Proton
(iii) Neutron
(iv) None of these
4. Which of the following is a poly-atomic cation?
(i) Ammonium ion
(ii) Magnesium ion
(iii) Chloride ion
(iv) Bromide ion
5. Which of the following elements is potassium hydroxide made up of?
(i) Potassium and oxygen
(ii) Potassium and hydrogen
(iii) Potassium, hydrogen and oxygen
(iv) potassium only
6. Which of the following is a mono-atomic molecule?
(i) Helium
(ii) Hydrogen
(iii) Chlorine
(iv) Oxygen
(B) Fill in the blanks: (1 marks each)
1. Pure substances are classified into element and compounds.
2. Pure substances have definite properties and definite composition.
3. The positive ion is called cation and the negative ion is called anion.
4. Electrons were discover by J. J. Thompson.
5. The combining capacity of elements is known as valency.
(C) Write T for true and F for False: (1 marks each)
1. Atoms of certain element combine to form molecules of those elements. T
2. Baking soda is not a compound. F
3. Poly-atomic molecules are made up of more than three atoms. T
4. Radicals are molecular species carrying a net charge. T
5. Metalloids are those substances which shows the property of neither metal nor non-metal. F
(D) Answer the following questions in brief: (2 marks each)
1. How are mixtures classified on the basis of distribution of their constituent particles?
Ans: Mixtures are classified based on the distribution of constituent particles as homogeneous when evenly distributed, creating a uniform appearance, and heterogeneous when unevenly distributed, resulting in distinct phases or regions within the mixture.
2. Give use of separating funnel.
Ans: A separating funnel is employed to separate immiscible liquids, like oil and water, by exploiting their density difference. It aids in isolating the heavier liquid at the bottom outlet for practical extraction and purification purposes.
3. Define the following: (i) Solution, (ii) Alloy
Ans: (i) Solution: A homogeneous mixture where a solute is uniformly dissolved in a solvent, resulting in a single-phase liquid or gas.
(ii) Alloy: A solid mixture of two or more elements, typically metals, with enhanced properties compared to their individual components.
4. Explain the following terms: (i) Valency, (ii) Radicals
Ans: (i) Valency: A measure of an element's combining capacity, indicating the number of electrons it can gain, lose, or share in chemical reactions.
(ii) Radicals: Groups of atoms or molecules with unpaired electrons, often reactive, that act as single units in chemical reactions.
5. Give one difference between molecule of an element and molecule of a compound.
Ans: A molecule of an element consists of identical atoms of the same element, while a molecule of a compound comprises different types of atoms bonded together to form a distinct chemical substance.
(E) Answer the following questions in detail: (3 marks each)
1. Give postulates of Dalton's atomic theory.
Ans: (i) Elements and Atoms: Elements are composed of indivisible particles called atoms.
(ii) Conservation of Mass: Chemical reactions involve the rearrangement of atoms, and the total mass remains constant.
(iii)Multiple Proportions: When elements combine to form compounds, they do so in simple whole-number ratios of their masses.
(iv) Definite Proportions: Compounds always have the same fixed composition, determined by the ratio of atoms.
(v) Atomic Theory: Dalton's atomic theory laid the foundation for modern atomic theory, emphasizing the importance of atoms in chemistry.
2. Define atomicity. How are molecules classified on the basis of their atomicity?
Ans: Atomicity refers to the number of atoms that constitute a molecule. Molecules are classified into three categories based on atomicity: diatomic molecules consist of two atoms of the same or different elements (e.g., O2, HCl), triatomic molecules contain three atoms (e.g., H2O, CO2), and polyatomic molecules consist of four or more atoms (e.g., CH4, C6H12O6).
3. What are poly-atomic ions? Name two poly-atomic cations and anions.
Ans: Polyatomic ions are groups of two or more atoms that carry a net electric charge and act as a single unit in chemical reactions. Examples of polyatomic cations include ammonium (NH4+) and hydronium (H3O+). Polyatomic anions include sulfate (SO4²-) and nitrate (NO3-). These ions play crucial roles in various chemical compounds and reactions, contributing to the diversity of ionic compounds in chemistry.
4. Give a brief summary of the differences of elements, compounds and mixtures.
Ans: Elements are pure substances composed of identical atoms, like oxygen (O2). Compounds consist of different atoms chemically bonded together, forming distinct substances, such as water (H2O). Mixtures are combinations of substances physically mixed without chemical bonding; they can be homogeneous (uniform composition, like saltwater) or heterogeneous (non-uniform, like a salad). Elements and compounds maintain fixed compositions, while mixtures can vary in composition and can be separated physically.
5. Explain how fractional distillation is used to separate miscible liquids.
Ans: Fractional distillation is a separation technique used to separate miscible (mixable) liquids with different boiling points. In a fractionating column, the mixture is heated. The component with the lower boiling point vaporizes first, rises through the column, and condenses at a certain height. This process is repeated for each component, allowing the separation of liquids based on their boiling points, which results in distinct fractions collected at different levels.
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