Case study Questions in Class 9 Science Chapter 3 are very important to solve for your exam. Class 9 Science Chapter 3 Class 9 Science Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving case study-based questions for Class 9 Science Chapter 3 Atoms and Molecules
In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.
Atoms and Molecules Case Study Questions With Answers
Here, we have provided case-based/passage-based questions for Class 9 Science Chapter 3 Atoms and Molecules
Case Study/Passage-Based Questions
Case Study 1: The knowledge of the valencies of various radicals helps us to write the formulae of chemical compounds. The total positive charge on positive ions (cations) is equal to the total negative charge on negative ions (anions) in a molecule. Therefore, in writing the formula of a compound, the positive and negative ions are adjusted in such a way that the total number of positive charges of positive ions (cations) becomes equal to the total number of negative charges of negative ions (anions).
There is another simple method for writing the formulae of ionic compounds. In this method, the valencies (or positive or negative charges) of the ions can be ‘crossed over’ to give subscripts. The purpose of crossing over of charges is to find the number of ions required to equalise the number of positive and negative charges.
Element X has two valencies 5 and 3 and Y has valency 2. The elements X and Y are most likely to be respectively
(a) copper and sulphur
(b) sulphur and iron
(c) phosphorus and fluorine
(d) nitrogen and iron.
Answer: (d) nitrogen and iron.
The formula of the sulphate of an element X is X2(SO4)3. The formula of nitride of element X will be
(a) X2N (b) XN2
(c) XN (d) X2N3
Answer: (c) XN
The formula of a compound is X3Y. The valencies of elements X and Y will be respectively
(a) 1 and 3 (b) 3 and 1
(c) 2 and 3 (d) 3 and 2
Answer: (a) 1 and 3
Case Study/Passage Based Questions
Case Study 2: A mole of an atom is a collection of atoms whose total mass is the number of grams equal to the atomic mass. Since an equal number of moles of different elements contain an equal number of atoms it becomes convenient to express the amounts of the elements in terms of moles. A mole represents a definite number of particles viz, atoms, molecules, ions or electrons. This definite number is called the Avogadro number or Avogadro constant which is equal to 6.022 × 1023. Hence a mole represents 6.022 × 1023 particles of the substance. One mole of a substance represents one gram-formula of the substance. One mole of a gas at standard temperature and pressure occupies 22.4 litres.
How many grams of sodium must be taken to get 1 mole of the element?
(a) 23 g (b) 35.5 g
(c) 63.5 g (d) 46 g
Answer: (a) 23 g
What is the mass in grams of a single atom of chlorine? (Atomic mass of chlorine = 35.5)
(a) 6.54 × 1023 g (b) 5.9 × 10–23 g
(c) 0.0025 g (d) 35.5 g
Answer: (b) 5.9 × 10–23 g
How many number of moles are there in 5.75 g of sodium ?
(Atomic mass of sodium = 23)
(a) 0.25 (b) 0.5
(c) 1 (d) 2.5
Answer: (a) 0.25
What is the mass in grams of 2.42 mol of zinc? (Atomic mass of Zn = 65.41)
(a) 200 g (b) 25 g
(c) 85 g (d) 158 g
Answer: (d) 158 g
Case Study/Passage-Based Questions
Case Study 3: According to Dalton’s atomic theory, all matter whether an element, a compound, or a mixture is composed of small particles called atoms which can neither be created nor destroyed during a chemical reaction. Dalton’s theory provides a simple explanation for the laws of chemical combination. He used his theory to explain the law of conservation of masses, the law of constant proportions, and the law of multiple proportions, based on various postulates of the theory. Dalton was the first scientist to use the symbols for the elements in a very specific sense. When he used a symbol for an element he also meant a definite quantity of that element, that is one atom of that element.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
(a) Atoms can neither be created nor destroyed.
(b) Each element is composed of extremely small particles called atoms.
(c) All the atoms of a given element are identical.
(d) During chemical combination, atoms of different elements combine in simple ratios.
Answer: (a) Atoms can neither be created nor destroyed.
Which postulate of Dalton’s atomic theory explains law of definite proportions?
(a) Atoms of an element do not change during a chemical reaction.
(b) An element consists of atoms having fixed mass and the number and kind of atoms in a given compound is fixed.
(c) Different elements have different kind of atoms.
(d) Atoms are of various kinds
Answer: (b) An element consists of atoms having fixed mass and the number and kind of atoms in a given compound is fixed.
“If 100 g of calcium carbonate (whether in the form of marble or chalk) is decomposed, 56 g of calcium oxide and 44 g of carbon dioxide are formed.” Which law of chemical combination is illustrated by this statement?
(a) Law of constant proportions
(b) Law of conservation of mass
(c) Law of multiple proportions
(d) Law of conservation of energy
Answer: (b) Law of conservation of mass
When 5 g calcium is burnt in 2 g oxygen, 7 g of calcium oxide is produced. When 5 g of calcium is burnt in 20 g of oxygen, then also 7 g of calcium oxide is produced. Which law of chemical combination is being followed?
(a) Law of conservation of mass
(b) Law of multiple proportions
(c) Law of constant proportions
(d) No law is being followed.
Answer: (c) Law of constant proportions
Case Study 4: Atoms and molecules are the building blocks of matter. An atom is the smallest unit of an element that retains its chemical properties, while a molecule is a group of two or more atoms held together by chemical bonds. Atoms consist of a positively charged nucleus, which contains protons and neutrons, surrounded by negatively charged electrons in energy levels or shells. The number of protons in an atom determines its atomic number and defines its unique identity as an element. The electrons in an atom occupy specific energy levels, and the outermost shell is known as the valence shell. Atoms gain, lose, or share electrons to achieve a stable electron configuration, forming chemical bonds and giving rise to molecules. Understanding the concept of atoms and molecules is crucial for comprehending various chemical reactions and the composition of substances.
What is the smallest unit of an element that retains its chemical properties?
Answer: d) Atom
What is a group of two or more atoms held together by chemical bonds called?
Answer: c) Molecule
What are the positively charged particles present in the nucleus of an atom called?
d) Valence electrons
Answer: b) Protons
Which part of an atom contains electrons in energy levels or shells?
d) Valence shell
Answer: d) Valence shell
What do atoms do to achieve a stable electron configuration?
a) Gain, lose, or share electrons
b) Absorb protons
c) Increase their atomic number
d) Create chemical bonds
Answer: a) Gain, lose, or share electrons
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