ATOMS AND MOLECULES

ATOMS AND MOLECULES

VERY SHORT ANSWER TYPE QUESTIONS (VSAQ)

1. Who established the Law of Conservation of Mass? Ans :- Antoine Lavoisier and Joseph L. Proust. 2. What does the La...

11. What does the Law of Constant Proportion state? Ans :- The law says that in any compound, the elements are always p...

21. Define law of constant proportion. Ans :- The law of constant proportion says that in a pure chemical substance, t...

31. How is molecular mass measured? Ans :- It is measured in atomic mass units (u). 32. What is the molecular mass of...

41. What are monoatomic molecules? Ans :- Monoatomic molecules consist of only one atom, like argon (Ar) and helium (He...

51. State the law of conservation of mass. Ans :- This law says that in a chemical reaction, mass cannot be made or l...

SHORT ANSWER TYPE QUESTIONS (SAQ)

1. What is the Law of Conservation of Mass? Ans :- The Law of Conservation of Mass states that mass cannot be created...

2. Ca2P2O7 is the formula of calcium pyrophosphate. Write the formula for ferric pyrophosphate. Ans :- Valency of cal...

3. What is the mass of (i) 2.5 moles of CO2 and (ii) 1 mole of water? Ans :- (i) 1 mole of CO2 = Molecular mass expre...

4. Define valency. Ans :- Valency is the ability of an element to combine with other elements by gaining, losing, or...

5. Who were the key scientists behind the Law of Conservation of Mass? Ans :- Antoine Lavoisier and Joseph L. Proust w...

6. What is the purpose of using a cork in the flask during the experiment? Ans :- The cork is used to make sure no sub...

7. The mass of one molecule of a substance is 4.65 × 1023 grams. What is its molecular mass? Ans :- Mass of 1 molecul...

8. Why is mass measured before and after mixing the chemicals in the experiment? Ans :- Mass is measured before and af...

9. Define the atomic mass unit. Ans :- One atomic mass unit is the mass equal to exactly one-twelfth (1/12th) of the...

10. What happens to the mass when a chemical reaction takes place in a closed system? Ans :- In a closed system, the m...

11. What is radioactivity? What are the applications of radioisotopes? Ans :- Radioactivity is when energy is release...

12. What is the Law of Constant Proportion, and can you give an example? Ans :- The Law of Constant Proportion states...

13. Define the term gram atom. How is it related to mole and Avogadro number? Ans :- The atomic mass of an element ex...

14. What are the key points of John Dalton’s Atomic Theory? Ans :- Dalton's Atomic Theory says all matter is made of i...

15. Write down the names of compounds represented the following formulae: (a) Al2(SO4)3 Ans :- Al2(SO4)3 - Alumini...

17. Why are atoms important, and how small are they? Ans :- Atoms are crucial because they are the basic building bl...

18. How are modern symbols for elements created, and what does IUPAC do? Ans :- Modern symbols for elements are usua...

19. How is atomic mass defined and what standard is used today? Ans :- Atomic mass is defined as the mass of an atom...

20. What are molecules? Give brief explanation of the arrangement of the constituent atoms in the molecules. Ans :-...

21. Why do atoms not exist independently and how do they form matter? Ans :- Atoms do not exist independently becaus...

22. What is the difference between molecules of elements and molecules of compounds? Ans :- Molecules of elements co...

23. What are ions, and how do they form? Ans :- Ions are charged particles that form when atoms gain or lose electro...

24. What is the difference between molecular mass and formula unit mass? Ans :- Molecular mass is the sum of atomic...

25. How do you calculate the molecular mass of a compound like H₂O? Ans :- To calculate the molecular mass of H₂O, a...

26. What is meant by the term chemical formula? Ans :- The chemical formula of a compound is a way to show what it...

27. Find the percentage of water of crystallization in FeSO4.7H2O. Ans :- Atomic mass of – Fe = 55.9u, S = 32u, H =...

28. What is the mass of – Atomic mass of – S = 32u, Al = 27u, Na = 23u, N = 14u, O = 16u (a) 1 mole of nitrogen atoms?...

29. There are two elements C and B. C emits an α – particle and B emits a β – particle. How will the resultant elements...

30. Explain the law of multiple proportions. Ans :- The law of multiple proportions says that when two elements comb...

31. Explain the form of atoms in a solid. Ans :- A solid element is made up of many atoms grouped together. The prop...

32. Calculate the formula unit masses of ZnO, Na2O, K2CO3 given atomic masses of Zn = 65u, Na = 23u, K = 39u, C = 12u, a...

33. The mass of any single atom X is 3.05 × 10-22 g. What is its atomic weight? Name the possible element. Ans :- 1...

34. Give the names of the elements present in the following compounds. (a) Quick lime Ans :- Quick lime –CaO Element...

LONG ANSWER TYPE QUESTIONS (LAQ)

1. Explain the Law of Conservation of Mass and how it can be demonstrated with an experiment. Ans :- The Law of Conser...

2. What is the significance of atoms in matter, and how are their symbols determined? Ans :- Atoms are fundamental uni...

3. What is atomic mass, and how is it determined? Ans :- Atomic mass is a measurement that indicates the mass of an ato...

4. Explain what a molecule is and the different types of molecules. Ans :- A molecule is the smallest particle of an el...

5. If one mole of carbon atoms weighs 12 grams, what is the mass (in grams) of one atom of carbon? Ans :- It is known...

6. What are ions, and what roles do they play in compounds? Ans :- Ions are charged particles formed when atoms either...

7. Explain how to calculate the molecular mass of a compound, using water (H2O) as an example. Ans :- To find the molec...

8. Convert into mole. Atomic mass of – C = 12u, H = 1u, O = 16u (a) 12 g of oxygen gas Ans :- Molar mass of O2 = (16...

9. What is formula unit mass, and how is it calculated using calcium chloride (CaCl2) as an example? Ans :- Formula uni...

10. What is the use of mole concept? Ans :- Applications of mole concept : (i) We can calculate the number of basic p...

11. 50 g of 10% lead nitrate is mixed with 50 g of 10% sodium chloride in a closed vessel. It was found after reaction t...

12. What is the mass of : (a) 1 mole of nitrogen atoms? (b) 4 moles of aluminium atoms (atomic mass of aluminium = 27)?...

13. Give the postulates of Dalton’s atomic theory. Ans :- Every element is made up of tiny particles called atoms. Ato...

14. State the Postulates of Dalton Theory? Ans :- Dalton's atomic theory says that everything, whether it's an element...

15. Which element will be more reactive and why – the element whose atomic number is 10 or the one whose atomic number i...

16. In a reaction, 5.3g of sodium carbonate reacted with 6g of ethanoic acid. The products were 2.2g of carbon dioxide,...

17. (a) Give one point of difference between an atom and an ion. (b) Give one example each of a polyatomic cation and an...

18. When 3.0 g of magnesium is burnt in 2.00 g of oxygen, 5.00 g of magnesium oxide is produced. What mass of magnesium...

19. Glucose has the molecular formula C6H12O6. Calculate : (a) Its molecular mass. (b) The number of atoms in one molecu...

20. A 0.24g sample of compound of oxygen and boron was found by analysis to contain 0.096g of boron and 0.144g of oxygen...

21. What are the failures of Dalton's Atomic theory? Ans :- It didn't consider smaller particles inside atoms. Dalton'...

22. Calculate the Molecular Mass of Atomic mass of – S = 32u, H = 1u, C = 12u, N = 14u, O =1 6u (a) Ammonium sulphate (N...

23. Calculate the number of H2O molecules in one drop of water having a mass of 0.05 g. Ans :- Number of moles of H2O...

24. What is the mass percentage of different elements in calcium carbonate? (Atomic mass : Ca = 40, O = 16) Ans :- Mol...

NCERT SOLUTION

1. In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dio...

Page No. 30 1. Define atomic mass unit. Ans :- An atomic mass unit (amu or u) i...

Page No. 34 1. Write down the formulae of (a) sodium oxide (b) aluminium chloride (c) sodium sulphide (d)...

2. Write down the names of compounds represented by the following formulae: (a) Al 2(SO 4) 3 (b) CaCl 2 (c)...

3. What is meant by the term chemical formula? Ans :- A chemical formula is a symbolic representation of a compound...

4. How many atoms are present in (a) H 2S molecule and (b) PO₄³- ion? Ans :- (a) H₂S molecule consi...

Page No. 35 1. Calculate the molecular masses of H 2, O 2, Cl 2, CO 2, CH 4, C 2H 6, C 2H 4...

2. Calculate the formula unit masses of ZnO, Na 2O, K 2CO 3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u,...

Page No. 36 1. A 0.24 g sample of a compound of oxygen and boron was found by analysis to c...

2. When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxid...

3. What are polyatomic ions? Give examples. Ans :- Polyatomic ions are charged groups of two or more ato...

4. Write the chemical formulae of the following. (a) Magnesium chloride (b) Calcium oxide (c) Copper nitrate (d) Alu...

5. Give the names of the elements present in the following compounds. (a) Quick lime (b) Hydrogen bromide (c) Baking...

6. Calculate the molar mass of the following substances. (a) Ethyne, C 2H 2 (b) Sulphur molecule, S8 (c) Phospho...

SUMMARY

Introduction For thousands of years, people have been curious about what matter is made of. In ancient India, around 5...

Laws of Chemical Combination The Laws of Chemical Combination help us understand how substances interact and combine...

2. Law of Constant Proportion The Law of Constant Proportion, also called the Law of Definite Proportion, says that in...

What is an Atom? An atom is the basic building block of matter. Just like a small grain of sand is the building block of...

Atomic Mass One of the key ideas in Dalton's atomic theory is the concept of atomic mass. Dalton suggested that each ele...

What is a Molecule? A molecule is a group of two or more atoms that are chemically bonded together. This means they are...

Writing Chemical Formulae A chemical formula is a way to show what a compound is made of using symbols for the elements...

Molecular Mass and Formula Unit Mass Molecular Mass is the total mass of a molecule, calculated by adding the atomic mas...