CBSE Class 9 Science Atoms and Molecules Sure Shot Questions C

CBSE Class 9 Science Atoms and Molecules Sure Shot Questions C. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

ATOMS AND MOLECULES

1. Avogadro’s number represents the number of atoms in

     (a) 12_g of C₁₂         (b) 320g of sulphur

     (c) 32g of oxygen     (d) 12.7g of iodine

2. The number of moles of carbon dioxide which contain 8 g of oxygen is

     (a) 0.5 mol         (b) 0.20 mol

     (c) 0.40 mol        (d) 0.25 mol

3. The total no of ions present in 111 g of CaCl₂ is

      (a) One mole     (b) Two mole

      (c) Three mole    (d) Four moles

4. Which of the following weighs the most ?

      (a) one g-atom of nitrogen    (b) One mole of water

      (c) One mole of sodium       (d) One molecule of H₂SO₄

5. 5.0 litre of 0.4 M H₂SO₄ Contains-

      (a) 2.0 Mole Of H₂SO₄       (b) 0.4 mole H₂SO₄

      (c) 5.0 mole H₂SO₄              (d) 2.0 moles H₂O

6. Which of the following correctly represents 360 g of water?

     (i) 2 moles of H₂0

     (ii) 20 moles of water

     (iii) 6.022 × 1023 molecules of water

     (iv) 1.2044×1025 molecules of water

     (a) (i) (b) (i) and (iv)

     (c) (ii) and (iii) (d) (ii) and (iv)

7. Which of the following statements is not true about an atom?

     (a) Atoms are not able to exist independently

     (b) Atoms are the basic units from which molecules and ions are formed

     (c) Atoms are always neutral in nature

     (d) Atoms aggregate in large numbers to form the matter that we can see, feel or touch

8. The chemical symbol for nitrogen gas is

     (a) Ni (b) N2 (c) N+ (d) N

9. The chemical symbol for sodium is

     (a) So (b) Sd (c) NA (d) Na

10. Which of the following would weigh the highest?

      (a) 0.2 mole of sucrose (C₁₂ H₂₂ O₁₁)
       (b) 2 moles of CO₂
       (c) 2 moles of CaCO₃
       (d) 10 moles of H₂O.

11. Which of the following has maximum number of atoms? (a) 18g of H₂O

(b) 18g of O₂

(c) 18g of CO₂

(d) 18g of CH₄

12.Which of the following contains maximum number of molecules? (a) 1g CO₂

(b) 1g N2

(c) 1g H2

(d) 1g CH4

13.Mass of one atom of oxygen is

(a) 16/6.023 x10²³ g

(b)32/6.023 x 10²³ g

(c) 1/6.023 x 10²³ g

(d )8u

14. 3.42 g of sucrose are dissolved in 18g of water in a beaker. The number of oxygen atoms in the solution are

(a) 6.68 × 10²³

(b) 6.09 × 10²² (c) 6.022 × 10²³ (d) 6.022 × 10²¹

15. A change in the physical state can be brought about

(a) only when energy is given to the system

(b) only when energy is taken out from the system

(c) when energy is either given to, or taken out from the system

(d) without any energy change

16. Which of the following represents a correct chemical formula? Name it. (a) CaCl (b) BiPO₄ (c) NaSO₄ (d) NaS

17. Write the molecular formulae for the following compounds

(a) Copper (II) bromide

(b) Aluminium (III) nitrate (c) Calcium (II) phosphate (d) Iron (III) sulphide

(e) Mercury (II) chloride

(f) Magnesium (II) acetate

18. SO^2- ,Cu²⁺, Na+, Fe³⁺, C1–,Write the molecular formulae of all the compounds that can be formed by the combination of following ions PO^3-

19. Write the cations and anions present (if any) in the following compounds

(a) CH₃COONa

(b) NaCl

(c) H2

(d) NH₄NO₃

20. Give the formulae of the compounds formed from the following sets of elements

(a) Calcium and fluorine

(b) Hydrogen and sulphur (c) Nitrogen and hydrogen (d) Carbon and chlorine

(e) Sodium and oxygen

(f) Carbon and oxygen

21. 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

22. Give the chemical formulae for the following compounds and compute the ratio by mass of the combining elements in each one of them.

(a) Ammonia

(b) Carbon monoxide (c) Hydrogen chloride (d) Aluminium fluoride (e) Magnesium sulphide

23. State the number of atoms present in each of the following chemical species

(a) CO32–

(b) PO43–

(c) P2O5

(d) CO

24. Find the ratio by mass of the combining elements in the compound – C₂H₅OH.

25. Give the formula of the compound formed by the elements calcium and fluorine.

26.What is the acid radical present in sodium peroxide?

27.Carbon and silicon have the same valency. What is the formula of sodium silicate?

28.What is the ratio by number of atoms in mercurous chloride?

29.Name the element whose Latin name is Stibium.

30.What is the valency of a sulphide ion?

31.How many atoms of oxygen are present in 50g of CaCO₃?

32.How many molecules are present in 1 ml of water?

33.What is the unit of measurement of atomic radius?

34.Name the international organization who approves names of elements.

35.How do we know the presence of atoms if they do not exist independently for most of the elements?

36.Give an example to show Law of conservation of mass applies to physical change also.

37.Explain with example that law of conservation of mass is valid for chemical reactions.

38.Is there any exception to law of conservation of mass?

39.In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water

40.If 12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon dioxide will be formed?

41.A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

42.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 dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?

43.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?

44.Why are Dalton's symbol not used in chemistry?

45.What is the fraction of the mass of water due to neutrons?

46.Does the solubility of a substance change with temperature? Explain with the help of an example.

47.Classify each of the following on the basis of their atomicity.

48.You are provided with a fine white coloured powder which is either sugar or salt. How would you identify it without tasting?

49.Calculate the number of moles of magnesium present in a magnesium ribbon weighing 12 g. Molar atomic mass of magnesium is 24g mol–1.

50.Verify by calculating that
(a) 5 moles of CO₂ and 5 moles of H2O do not have the same mass.
(b) 240 g of calcium and 240 g magnesium elements have a mole ratio of 3:5.

51.Find the ratio by mass of the combining elements in the following compounds. (a) CaCO₃ (d) C₂H5OH
(b) MgCl₂ (e) NH3
(c) H₂SO₄ (f) Ca(OH)₂

52.Calcium chloride when dissolved in water dissociates into its ions according to the following equation.
CaCl₂ (aq) →Ca2+ (aq) + 2Cl– (aq)
Calculate the number of ions obtained from CaCl₂ when 222 g of it is dissolved in water.

53.The difference in the mass of 100 moles each of sodium atoms and sodium ions is 5.48002g. Compute the mass of an electron.

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