Title Class 09 Science 3 Atoms and Molecules.pdf ✅

Atoms and Molecules DPP-01 [Topic: Atoms, Symbols of elements, Atomic mass, Molecules of elements and compounds, Ions, Writing chemical formula, Molecular mass, Formula unit mass] Very Short Answer Type Questions 1. What is meant by the term chemical formula? 2. How many atoms are present in a: (i) H2S molecule (ii) PO4 3− ion? 3. Name the unit in which atomic radius is measured. 4. Define molecular mass. 5. What is the formula unit mass? 6. Name the element used as a standard for atomic mass unit. 7. In what form does oxygen occur in nature? 8. In what form noble gases exist in nature? 9. What is the difference between 2H and H2 ? 10. Calculate formula unit mass of Mg(NO3)2. (Mg = 24u,N = 14u, O = 16u) 11. Define the atomic mass unit. 12. Why is it not possible to see an atom with naked eyes? 13. Define atomicity. 14. How many atoms are present in one molecule of ozone? 15. Give an example of: (a) Triatomic, (b) Polyatomic molecules of elements. 16. Define law of constant proportion. 17. What is the ratio between mass of carbon and oxygen in CO2 ? (C = 12uuO = 16uu) 18. Name the anion and cation present in molecule of magnesium oxide. 19. An element ' X ' has valency 3. Write the formula of its oxide. 20. Write the names of compounds (aa)Ag2O(b) CuS 21. Write the symbol for following elements ( (aa) Iron (bb) Potassium 22. Give the difference between a cation and an anion?

(c) Baking powder (d) Potassium sulphate 36. As per law of definite proportions, carbon and oxygen combine in the ratio of 3: 8. Compute the mass of oxygen that would be required to react completely with 6g of carbon. 37. Find the formula unit mass of (aa)NaHCO3(bb)Na2CO3 38. Select the element that is (aa) ductile, (bb) conductor of electricity, (cc) a constituent of water, (d) non-metal, liquid at room temperature. 39. Hydrogen and Oxygen combine in the ratio 1: 8 by mass for water. What mass of oxygen gas would be required to completely react with 4g of hydrogen gas? 40. Classify the following compounds as diatomic, triatomic and polyatomic molecule: HCl,H2,H2O,NH3 41. Write the cations and anions present (if any) in the following compounds: (a) CH3COONa (b) NaCl (c) H2 (d) NH4NO3 42. Which of the following symbols of elements are incorrect? Give their correct symbols. (a) Cobalt- CO (b) Carbon-C (c) Aluminium - Al (d) Helium- He (e) Sodium -So Short Answer Type Questions-II 43. Write down the names of compounds represented by the following formula: (a) Al2(SO4)3 (b) CaCl2 (c) K2SO4 (d) KNO3 (e) CaCO3. 44. Calculate the formula unit masses of ZnO, Na2O, K2CO3. [Atomic mass of Zn = 65uu, O = 16uuNa = 23uu, K = 39uu, C = 12uu] 45. What is the difference between homoatomic and heteroatomic molecules? Illustrate with the help of four examples each? 46. 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. Calculate the percentage composition of the compound by weight. 47. When 3.0g of carbon is burnt in 8.0g oxygen, 11.0g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.0g of carbon is burnt in 50.0g of oxygen? Which law of chemical combination will govern your answer?