CBSE Class 9 Science, Atoms and Molecules: Important topics and questions
Check out the important terms/topics given below:
• Name of scientists who established the two important laws of chemical combinations?
• Write the chemical formulae of the given compounds:
(i) Copper sulphate sodium carbonate
(ii) Barium chloride sodium sulphate
(iii) Lead nitrate sodium chloride
• Concept of law of conservation of mass and law of chemical combination with examples
• E = mc2 follows the law of conservation of mass or not
• Calculations based on numerical problems to make an agreement for the law of conservation of mass
• 2.8 gram of N2 gas was allowed to react with 0.6 gram of hydrogen gas to produce 3.4 gram of ammonia. Show that these observations are in agreement with the law of conservation of mass
• Postulates of Dalton’s atomic theory
• Law of definite proportion
• Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
• Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
• Full form of IUPAC
• Name of atoms and their symbols
• Homo atomic molecules and heteroatom molecules
• Concept of atomicity and its formula to calculate the same
• Definition of isotopes, isotones, and isobars with examples
• Identify the isotopes, isotones, and isobars from the given pairs
a. (17Cl35, 17Cl37)
b. (18Ar40, 20Ca 40)
c. (6C13, 7N14 )
• Find the atomicity of chlorine if its atomic mass is 35.5 and molecular mass is 71
• Find the atomicity of ozone if its atomic mass is 16 and molecular mass is 48
• Concept of relative atomic mass and relative molecular mass
• Define 1 amu
• A very fine study about the mole concept. Different ways to calculate the number of moles
• Concept of ion formation and generation of positive and negative charges
• Cross valency concept to write the formula of compound
• Always focus on the concept given in your book rather than different materials from different books or sites
Important Questions are as below:
Q. Magnesium and oxygen combine in the ratio of 3:2 by mass to form magnesium oxide. How much oxygen is required to react completely with 12 g of magnesium?
Q. Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q. Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature.
(d) Atoms combine together to form matter that we can see, feel, or touch.
Q. A sample of vitamin C is known to contain 2.58 ×1024 oxygen atoms. How many moles of oxygen atoms are present in the sample?
Q. If bromine atom is available in the form of, say, two isotopes 7935Br (49.7%) and 8135Br (50.3%), calculate the average atomic mass of bromine atom.
Q. Which has more number of atoms, 100g of N2 or 100 g of NH3?
Q. Calculate the relative molecular mass of water (H2O)
Q. Calculate the formula unit masses of ZnO, Na2O, and K2CO3.
[Given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u]
Q. Write the chemical formulae of the following.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.
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