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Worksheet for Class 9 Science Chapter 3 Atoms and Molecules
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Class 9 Science Worksheet for Chapter 3 Atoms and Molecules
Exam Questions NCERT Class 9 Science Chapter 3 Atoms And Molecules
Question. Give Latin name of Silver.
Answer : Latin name of Silver is ‘Argentum’.
Question. If 9 g of water is decomposed, how many grams of hydrogen and oxygen are obtained?
Answer : If 9 g of water is decomposed, 1 g of hydrogen and 8 g of oxygen are always obtained.
Question. Name the two laws of chemical combination.
Answer : Law of conservation of mass and law of constant proportions.
Question. Why is it not possible to see an atom with naked eyes?
Answer : Because an atom is too small, i.e., the atomic radii of an atom is of the order 10–19 m to 10–9 m.
Question. Define the atomic mass unit.
Answer : The mass of th 12 1 part of C-12 is equivalent to one atomic mass unit. Previous, it was denoted by symbol ‘amu’ but nowadays it is denoted by symbol ‘u’.
Question. Which organisation approves the names of elements all over the world?
Answer : International Union of Pure and Applied Chemistry (IUPAC).
Question. What is Avogadro number?
Answer : The number 6.022 × 1023 is referred to as Avogadro number and is denoted by symbol NA.
Question. What is the similarity between chlorine molecule, nitrogen molecule and hydrogen molecule?
Answer : Chlorine molecule, nitrogen molecule and hydrogen molecule are diatomic molecules. These are formed by the union of two atoms of the same element.
Question. What is the symbol of the element of molybdenum?
Answer : ‘Mo’ is the symbol of the element of molybdenum.
Question. What is the latest short form of atomic mass unit?
Answer : The latest short form of atomic mass unit is u, according to IUPAC.
Question. Write the chemical symbols of two elements which are formed from the first letter of the elements’ name.
Answer : N (Nitrogen), F (Fluorine), I (Iodine), O (Oxygen) (any two).
Question. Write the meaning of these formulae : (i) 2O, (ii) O2, (iii) O3
Answer : (i) 2O = Two atoms of oxygen
(ii) O2 = One molecule of oxygen
(iii) O3 = One molecule of ozone
Question. Why does the atomic mass of an element not represent the actual mass of its atom?
Answer : Atomic mass of an element is the mass of its atom on the atomic scale, on the other hand, the actual mass of an atom is obtained by dividing the atomic mass by Avogadro’s number.
Question. 8.4 g of sodium bicarbonate on reaction with 20 g of acetic acid liberated 4.4 g of carbon dioxide gas into the atmosphere. What is the mass of the residue left?
Answer : Total mass of reactants = 8.4 g + 20 g = 28.4 g
Total mass of reactants = Total mass of products
28.4 = 4.4 + x (mass of residue left)
28.4 – 4.4 = x ⇒ x = 24 g
Question. How many ions are there in 80 g of magnesium oxide?
Answer : Number of moles of magnesium oxide
= Mass of magnesium oxide / Molar mass of magnesium oxide = 80/40 =2
MgO Mg2+ + O2–
From the equation, we can see that 1 mol of MgO contains 1 mol of Mg2+ ions and 1 mol of O2– ions. 2.0 mol of MgO will contain 2.0 mol of Mg2+ ions and 2.0 mol of O2– ions.
Hence, 2.0 mol of MgO contains 4.0 mol of ions.Number of ions = 4 × 6.022 × 1023 = 2.4088 × 1024
Question. How many particles are represented by 0.25 mole of an element?
Answer : 1 mole of an element contains 6.022 × 1023 particles 0.25 mole of an element contains = 6.022 × 1023 × 0.25
= 1.5 × 1023 particles
Question. What are the postulates of Dalton’s atomic theory. Give at least four points.
Answer : The postulates of Dalton’s atomic theory may be stated as follows :
(i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties.
(iv) Atoms of different elements have different masses and chemical properties.
(v) Atoms combine in the ratio of simple whole number to form compounds.
(vi) The relative number and kinds of atoms are constant in a given compound.
Question. What is meant by a chemical formula? Give examples.
Ans : A chemical formula of a compound shows its constituent elements and the number of atoms of each combining element, e.g., chemical formula of ammonia is NH3, water is H2O and carbon dioxide is CO2.
Question. The atomic mass of an element is in fraction.” What does it mean?
Ans : If the atomic mass of an element is in fraction, this means that it exists in the form of isotopes. The atomic mass of such element is the average of atomic masses of its isotopes and is generally in fraction.
Question. 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 oxide will be formed when 3.00 g magnesium is burnt in 5.00 g of oxygen? Which law of chemical combination will govern your answer? State the law.
Ans : When 3.0 g of magnesium is burnt in 2.00 g of oxygen, 5.00 g of magnesium oxide is produced. It means magnesium and oxygen are combined in the ratio of 3 : 2 to form magnesium oxide.
Thus, when 3.00 g of magnesium is burnt in 5.00 g of oxygen, 5.00 g of magnesium oxide will be formed and the remaining oxygen will be left unused. It is governed by law of definite proportions.
It states that in a chemical substance, the elements are always present in definite proportions by mass.
Question. Calculate the following in 5.6 g of nitrogen :
(a) Number of moles of nitrogen
(b) Number of molecules of nitrogen
(c) Number of atoms of nitrogen
Ans : (a) Molar mass of nitrogen = 14 g
5.6 g of nitrogen = . 14 = 5 6 = 0.4 mole
(b) 28 g of nitrogen = 6.022 × 1023 molecules
5.6 g of nitrogen = 2.15 × 1022 molecules
(c) 14 g of nitrogen = 6.023 × 1023 atoms
5.6 g of nitrogen = 4.30 × 1023 atoms
Question. Write the chemical symbols of two elements which are formed from the first letter of the elements’ name.
Ans : N (Nitrogen), F (Fluorine), I (Iodine), O (Oxygen) (any two).
Question. What is the atomicity of argon?
Ans : Mono atomic.
Question.. Distinguish between molecular mass and molar mass.
Ans : The molecular mass of a substance is the sum of the atomic masses of all atoms in a molecule, whereas the mass of 1 mole of any substance is called its molar mass.
Question. Give the symbol of copper, silver, gold, oxygen, zinc.
Ans : Copper –
Cu Silver – Ag
Gold – Au
Oxygen – O
Zinc – Zn
Question. What is the building block of all matter?
Ans : Atom is the building block of all matter.
Question. What is the measuring unit of atomic radius?
Ans : Nanometre (nm) is the measuring unit of atomic radius.
Question. What is the difference between hydrogen chloride and nitrogen molecule formation?
Ans : Hydrogen chloride is molecular compound and formed by the union of different kinds of atoms while nitrogen is diatomic molecule and formed by union of two atoms of same kinds.
Question. Name two atoms which exist as independent atoms.
Ans : Noble gases such as argon (Ar) and helium (He) exist as independent atoms.
1M
1. The atomicity of noble gases is
(A) Mono-atomic
(B) Octa-atomic
(C) Tri-atomic
(D) Tetra-atomic
2. Write the formula of one polyatomic cation alongwith its valency. .
3. What is the mass of carbon dioxide released in the reaction ?
4. Calculate the number of molecules of carbon dioxide present in 4-4 g of it.
5. Law of Constant Proportions was given by
(A) Newton
(B) Rutherford
(C) Lavoisier
(D) Proust
6. 5g of Calcium (Ca) contains [Atomic mass of Ca = 40u]
(A) 1/8mol
(B) 1/7 mol
(C) 1/8g/mol
(D) 1/9mol
7. 1 mole of NH3 molecules contains
(A) 6.022X1023NH3 molecules
(B) 6.022X1022 NH3 atoms
(C) 6.022X1023 NH3 atoms
(D) 6.022X1022 NH3 molecules
8. Unit of molar mass is
(A) Gm/Molecule
(B) Gm
(C) Moles
(D) gm/mol
9. Valencies of iron are
(A) 2 and 3
(B) 1 and 3
(C) 1, 2 and 3
(D) 1 and 2
10. Cuprous sulphide is the chemical name of
(A) CuS
(B) Cu2S
(C) CuS2
(D) Cu3S
11. Mass of 0.5 M of oxygen atom is:
(A) 16 g
(B) 32 g
(C) 4 g
(D) 8 g
12. An ionic compound is made up of
(A) Metal-nonmetal
(B) Cation-Cation
(C) Anion-Anion
(D) None of the above
13. Write the chemical formula of "Aluminium phosphate".
14. Atom consists of electron, proton and neutron, which means it is divisible. This statement
(A) Strengthens Dalton's Atomic Theory
(B) Weakens Dalton's Atomic Theory
(C) Has no effect on Dalton's Atomic Theory
(D) None of the above
15. When 100g of CaCO3 was heated, it decomposes to yield 56g of CaO and 44g of CO2 . This statement proves that
(A) Mass is conserved during a chemical reaction
(B) There is complete loss of CaCO3 during a chemical reaction
(C) Mass of reactant is different from mass of product
(D) CaCO3 decomposes into Ca and CO2
16. Write down the formulae of aluminium sulphate and ethanol.
17. Which are called the building blocks of matter?
18. Write the chemical symbols of -
(c) Tin
(d) Mercury
19. How many metres are there in 1 nanometer (nm) ?
20. Define atomicity.
21. Atomicities of phosphorus and ozone are respectively:
(A) 4, 3
(B) 2, 2
(C) 2, 3
(D) 4, 2
22. What do we call those particles which have-
(a) Less electrons than the normal atoms.
(b) More electrons than the normal atoms.
23. Cation is formed due to
(A) Gain of electrons
(B) Loss of protons
(C) Loss of electrons
(D) Gain of protons
24. Match the following molar masses and choose the answer from the code given below
Column I Column II
(i) Sulphuric acid H2SO4 (A) 78g/mol
(ii) Benzene C6H6 (B) 164g/mol
(iii) Sodium Chloride NaCl (C) 98g/mol
(iv) Calcium nitrate (d) 58.5g/mol
[Atomic mass of: Ca = 40u, H = 1u, S = 32u, C = 12u, Na = 23u, N = 14u, O = 16u, Cl = 35.5u]
(A) (i) -C, (ii) -A, (iii) -D, (iv) -B
(B) (i) -B, (ii) -A, (iii) -D, (iv) -C
(C) (i) -C, (ii) -A, (iii) -B, (iv) -D
(D) (i) -A, (ii) -D, (iii) -C, (iv) -B
25. 144 grams of pure water is decomposed by passing electricity. 16 grams of hydrogen and 128 grams of oxygen are obtained. Which chemical law is illustrated by this statement?
26. What is the atomicity of -
(a) Ozone
(b) Nitrogen
27. What is the atomicity of -
(a) Neon
(b) Sulphur
28. What name is given to the number 6.023 x 1023?
29. Select the correct statement and choose the answer from the code given below-
I. Gram molecular mass of a substance contains 6.022X1023molecules.
II. The molar mass of a substance is the mass of 1 mole of that substance.
III. Gram molecular mass of H2O is 1.
IV. The molar mass of nitrogen molecule is 28g/mol
(A) I and III
(B) I, II and IV
(C) Only II
(D) All of these
30. Which of the following are ionic compounds?
(i) NH4+ (ii) CaCl2 (iii) C6H6 (iv) Al2O3
(A) (i) and (ii)
(B) (ii) and (iv)
(C) (i) and (iii)
(D) None of the above
31. Select the correct statement and choose the answer from the code given below
(i) All metals form cations by gaining electrons
(ii) All metals form cations by losing electrons
(iii) Hydrogen is a non metal but forms a cation
(iv) All nonmetals form anions
(A) (ii) only
(B) (iii) and (iv)
(C) (i) and (iii)
(D) (ii) , (iii) and (iv)
32. An atom is made up of negatively charged electrons and positively charged protons, still it is electrically neutral. The reason is
(A) The electrons and protons are equal in number so no net charge is present.
(B) The neutrons neutralize the charge and make the atom neutral
(C) The charge on the atom is too small to be detected
(D) Both (1) and (2)
33. When calcium metal (Ca) changes to calcium ion (Ca+2) the number of electron, proton andneutron
(A) Remains same
(B) Number of neutrons remains the same while the number of both protons and electrons changes.
(C) Number of neutrons and protons remains same while the number of electrons decreases by 2.
(D) Number of neutrons and electrons remains the same while number of protons increases by 2
34. What is the contradiction against Dalton's atomic theory in the formula of sucrose, C^22^u ?
35. Select the correct statement and choose the answer from the code given below
I.One mole of all substances in gaseous state contains equal number of particles (6.022X1023) and occupy equal volume (22.4 L) at STP.
II.One mole of all substances contains equal number of particles (6.022X1023) at all temperatures and pressure.
III.Avogadro number is equal to 6.022X1023 particles (atoms, molecules,ions) .
IV.One mole of N2 does not contain same number of molecules as in one mole of H2.
(A) I and IV
(B) I and III
(C) I, III and IV
(D) None of these
36. Write the postulate of Dalton's atomic theory that eplains the Law of definite proportions.
37. The number of atoms present in 0.4 mole of Calcium (Ca) are
(A) 2.408 X 1023
(B) 24.08 X 1023
(C) 2.408 X 1024
(D) 6.022 X 1023
38. An element A forms an oxide A2O3, the valency of A is
(A) 2
(B) 3
(C) 5
(D) 1
39. Formula mass of ammonium sulphate (NH4) 2SO4 is (N=14, H=1, O=16 and S=32)
(A) 114u
(B) 132u
(C) 120u
(D) 132u
40. The chemical formula of Phosphorus and Sulphur are respectively:
(A) P4 and S
(B) P3 and S8
(C) P4 and S8
(D) P4 and S6
41. Which of the following gases can exist in atomic form?
(A) Oxygen (O)
(B) Neon (Ne)
(C) Hydrogen (H)
(D) Nitrogen(N)
42. Define 'Atomic mass unit' or what is '1 «' ?
43. Write the formula of 'Limestone'. Name the elements present in it.
44. What is the molar mass of a sulphur molecule ?
45. What is Latin name of 'silver' ? What is its symbol ?
46. Write the chemical symbols of -
(a) Silver
(b) Potassium
47. Match the correct formula and choose the answer from the code given below
(i) Hydrogen sulphide (A) CuO
(ii) Ammonia (B) Al2O3
(iii) Aluminium oxide (C) H2S
(iv) Cupric Oxide (D) NH3
(A) (i) -C,(ii) -A,(iii) -D,(iv) -B
(B) (i) -A, (ii) -D, (iii) - C, (iv) -B
(C) (i) -C, (ii) -D, (iii) -B, (iv) -A
(D) (i) -B, (ii) -D, (iii) -A, (iv) -C
48. Calculate the mass of one amu in kilograms. .
49. Ratio of nitrogen and hydrogen in ammonia (NH3) by mass is:
(A) 3 : 1
(B) 1 : 3
(C) 3 :14
(D) 14 : 3
50. Which of the following statement is correct? Choose the answer from the code given below.
I Dalton proposed the term Atom
II.Maharishi Kanad proposed the term Atom
III.Atom was considered to be indivisible by Dalton
IV. Kanad said Atom could be further divided
(A) I only
(B) II and IV
(C) I and III
(D) All of these
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Worksheet for CBSE Science Class 9 Chapter 3 Atoms and Molecules
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