A abampere (aA) The unit of electric current in the CGSeniu system, defined as that current that, if flowing through two parallel conductors of negligible cross section and infinite length, placed 1 cm apart in vacuo, would produce on each conductor a force of 1 dyne per centimeter of length. 1 abampere = 1 abcoulomb/s = r statampere (where c = speed of light in cm/s) = 10 ampere. aberration Imperfect image formation due to geometric imperfections in the optical elements of a system ablation 1 . The wasting of glacier ice by any process (calving, melting, evaporation, etc.). 2. The shedding of molten material from the outer sur- face of a meteorite or tektite during its flight through the atmosphere. absolute age The age of a natural substance, of a fossil or living organism, or of an artifact, obtained by means of an absolute dating method. See absolute dating method. absolute density Density in kg/m' or, more commonly, in g/cm\ both at STP. Cf. density, relative density abso
Atoms and Molecules class 9 chemistry MCQ & SAQ
Atoms and Molecules class 9 chemistry NCERT SOLUTION
Q1. 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
Ans:
Mass of reactants = 5.3 g + 6 g = 11.3 g
Mass of products = 2.2 g + 0.9 g + 8.2 g = 11.3 g
Mass of reactants = Mass of products
Therefore, the Law of conservation of mass is proved.
Q2. Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3g of hydrogen gas?
Ans: Since hydrogen and oxygen combine in the ratio of 1:8 by mass, 3g of hydrogen gas will react completely with 24 g of oxygen gas.
Q3. Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?
Ans: Dalton’s postulate that “Atoms can neither be created nor destroyed,” is a result of the law of conservation of mass.
Q4. Which postulate of Dalton's atomic theory can explain the law of definite proportions?
Ans: Atoms combine in a fixed ratio to form compounds, which can explain the law of definite proportions.
Page No. 35
Q1. Define atomic mass unit.
Ans: It is defined as equal to 1/12th of the mass of 1 atom of C-12. It is called a unified mass denoted by 'u’ these days.
Q2. Why is it not possible to see an atom with naked eyes?
Ans: The size of an atom is so small that it is not possible to see it with naked eyes. Also, the atom of an element does not exist independently.
Page No. 39
Q1. Write down the formulae of
(a) sodium oxide
(b) aluminium chloride
(c) sodium sulphide
(d) magnesium hydroxide
Ans:
(a) Formula of Sodium Oxide
(b) Formula of Aluminium Chloride
(c) Formula of Sodium Sulphide
(d) Formula of Magnesium Hydroxide
Q2. Write down the names of compounds represented by the following formulae:
(a) Al2(SO4)3
(b) CaCl2
(c) K2SO4
(d) KNO3
(e) CaCO3
Ans:
(a) Aluminium sulphate
(b) Calcium chloride
(c) Potassium sulphate
(d) Potassium nitrate
(e) Calcium carbonate
Q3. What is meant by the term chemical formula?
Ans: The chemical formula of a compound is a symbolic representation of its composition.
Chemical Formula of Water
Q4. How many atoms are present in
(a) H2S molecule and
(b) PO43- ion?
Ans:
(i) H2S molecule has 2 atoms of hydrogen and 1 atom of sulphur hence 3 atoms in totality.
(ii) PO43- ion has 1 atom of phosphorus and 4 atoms of oxygen hence 5 atoms in totality.
Page No. 40
Q1. Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.
Ans:
Molecular mass of H2 = 2 × Atomic mass of H
= 2 × 1
= 2 u
Molecular mass of O2 = 2 × Atomic mass of O
= 2 × 16
= 32 u
Molecular mass of Cl2 = 2 × Atomic mass of Cl
= 2 × 35.5
= 71 u
Molecular mass of CO2 = Atomic mass of C2 × Atomic mass of O
= 12+ (2+16) = (12 + 32)u
= 44 u
Molecular mass of CH4= Atomic mass of C4 × Atomic mass of H
= 12+ (4 x 1)u = (12 + 4)u
= 16 u
Molecular mass of C2H6 = 2× Atomic mass of C6× Atomic mass of H
= (2 x 12 + 6 x 1)u = (24 + 6)u
= 30 u
Molecular mass of C2H4 = 2 x Atomic mass of C4 × Atomic mass of H
= (2 x 12 + 4 x 1)u = (24 + 4)u
= 28 u
Molecular mass of NH3 = Atomic mass of N3 × Atomic mass of H
= (14 + 3 x 1)u = (14 + 3)u
= 17 u
Molecular mass of CH3OH = Atomic mass of C3 × Atomic mass of H Atomic mass of O Atomic mass of H
= (12 + 3 x 1 + 16 + 1)u = (12 + 3 + 17)u
= 32 u
Q2. Calculate the formula unit masses of ZnO, Na2O, K2CO3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u.
Ans:
(i) Formula unit mass of ZnO
= 65 + 16 = 81 u
(ii) Formula unit mass of Na2O
= 2 x 23 + 16 = 46 + 16 = 62 u
(iii) Formula unit mass of K2CO3
= 2 x 39 + 12 + 3 x 16
= 78 + 12 + 48 = 138 u
Page No. 42
Q1. If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Ans:
1 mole of carbon atoms = 12 g
1 mole of carbon contains = 6.022 x 1023 atoms
6.022 x 1023 atoms weigh = 12 g
1 atom of carbon weighs = 12 / 6.022 x 1023
= 1.99 x 10-23 g
Q2. Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?
Ans:
No. of moles of Na = 100/23 = 4.34 moles
No. of moles of Fe = 100/56 = 25/14 = 1.79 moles
Since the number of moles of Na is more than the number of moles of Fe, therefore, 100 g of Na contains more number of atoms.
Page No. 43
Q1. A 0.24 g sample of a 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.
Ans:
Percentage of boron = (mass of boron / mass of the compound) x 100
= (0.096g / 0.24g) x 100
= 40%
Percentage of oxygen = 100 – percentage of boron
= 100 – 40
= 60%
Q2. 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 combinations will govern your answer?
Ans:
C + O2 → CO2
12 g of C reacts with 32 g of O2
3 g of C reacts with
3 g of carbon + 8 g of oxygen = 11 g of Carbon dioxide
3 g of carbon will react with only 8.0 g of oxygen to form 11 g of carbon dioxide.
50 - 8 = 42 g of O2 will remain unreacted.
The law of constant proportion will govern the answer because carbon and oxygen combine in a fixed ratio.
Q3. What are polyatomic ions? Give examples?
Ans: The ion which is made up of more than one atom is called a polyatomic ion.
Examples: PO43-, CO32-, NH4+
Q4. Write the chemical formulae of the following:
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.
Ans:
Q5. Give the names of the elements present in the following compounds:
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate
Ans:
(a) Quick lime contains calcium and oxygen.
(b) Hydrogen bromide contains hydrogen and bromine.
(c) Baking powder (NaHCO3) contains sodium, hydrogen, carbon and oxygen.
(d) Potassium sulphate contains potassium, sulphur and oxygen.
Q6. Calculate the molar mass of the following substances:
(a) Ethyne, C2H2
(b) Sulphur molecule, S8
(c) Phosphorus molecule, P4 (atomic mass of phosphorus = 31)
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO3
Ans:
(a) Molar mass of ethyne (C2H2) = 2 x 12 + 1 x 2 = 24 + 2 = 26 g
(b) Molar mass of sulphur molecule (S8) = 8 x 32 = 256 g
(c) Molar mass of phosphorus molecule (P4) = 4 x 31 = 124 g
(d) Molar mass of hydrochloric acid (HCI) = 1 + 35.5 = 36.5 g
(e) Molar mass of nitric acid (HNO3) = 1 + 14 + 3 x 16 = 1 + 14 + 48 = 63 g
Q7. What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na2SO3)?
Ans:
(a) Mass of 1 mole of nitrogen atoms = 14 g
(b) Mass of 1 mole of aluminium atoms = 27 g
Mass of 4 moles of aluminium atoms = 27 x 4 = 108 g
(c) Mass of 1 mole of Na2SO3 = 2 x 23 + 32 x 1 + 3 x 16
= 46 + 32 + 48 = 126 g
Mass of 10 moles of Na2SO3 = 126 x 10 = 1260 g
Q8. Convert into mole.
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide
Ans:
(a) 1 mole oxygen gas = 32 g
Number of moles of oxygen gas
(b) 1 mole of H2O = 2 + 16 = 18 g
Number of moles of H2O
(c) 1 mole of CO2 = 12 + 2 x 16 = 44 g
Number of moles of CO2
Q9. What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Ans:
(a) Mass of one mole of oxygen atoms = 16 g
Then, mass of 0.2 mole of oxygen atoms = 0.2 × 16g = 3.2 g
(b) Mass of 1 mole of H2O molecules
= 2 + 16 = 18 g
Mass of 0.5 mole of H2O molecules
= 0.5 x 18 g = 9 g
Q10. Calculate the number of molecules of sulphur (S8) present in 16 g of solid sulphur.
Ans:
Number of moles of sulphur
= 3.76 x 1023
Q11. Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(Hint: The mass of an ion is the same as that of an atom of the same element. The atomic mass of Al = 27 u)
Ans:
Molecular weight of Al2O3 = 2 x 27 + 3 x 16 = 54 + 48 = 102 g mol-1
102 g of Al2O3 contains 2 x 6.022 x 1023 Al3+ions
0.051 g of Al2O3 contains
Atoms and Molecules class 9 chemistry MCQ
1. What is the value of Avogadro’s number?
(a) 12.044 × 1022
(b) 6.022 × 1023
(c) 3.011 × 1023
(d) 6.022 × 1022
►
2. If 12 grams of carbon has n atoms, then the number of atoms in 12 grams of magnesium will be:
(a) 2n
(b) 3n
(c) n/2
(d) n
► (c) n/2
3. Which of the following is correct pair of elements and its symbol?
(a) Silver – Si
(b) Sodium – So
(c) Potassium – Pt
(d) Sulphur – S
► (d) Sulphur – S
4. A student heats 25g of reactant ‘A’ with 50g of reactant ‘B’. He obtains 50g of product ‘C’ and recovers 25 g of unreacted ‘B’. Which of the following law is confirmed in the following reaction?
(a) Law of constant proportion
(b) Law of conservation of mass
(c) Law of conservation of mass and Law of constant proportion
(d) Law of multiple proportion
► (c) Law of conservation of mass and Law of constant proportion
5. How many moles are present in 40 g of He?
(a) 10 moles
(b) 11 moles
(c) 13 moles
(d) 12 moles
► (a) 10 moles
6. Identify the symbol used to represent Avogadro’s number.
(a) MA
(b) AO
(c) AN
(d) NA
► (d) NA
7. Law of conservation of mass can be derived from which postulate of Dalton’s atomic theory?
(a) Atoms of a given element have same mass and chemical properties.
(b) Matter is made of tiny particles.
(c) Atom can neither be created nor destroyed.
(d) The relative number and kind of atoms are constant in a given compound.
► (c) Atom can neither be created nor destroyed.
8. Valency of hydrogen is 1 and that of sulphur is 2. What should be the formula of hydrogen sulphide?
(a) HS
(b) H2S2
(c) HS2
(d) H2S
► (d) H2S
9. Calculate the number of Mg atoms in 0.024 g of Mg
(a) 6.022 × 1021 Mg atoms
(b) 6.22 × 1023 Mg atoms
(c) 6.022 × 1020 Mg atoms
(d) 6.022 × 1025 Mg atoms
► (c) 6.022 × 1020 Mg atoms
10. Which of the following is the major drawback of Dalton’s atomic theory?
(a) Atoms of an element have exactly the same mass.
(b) Atoms are indivisible.
(c) Atoms of different elements have different masses.
(d) All of the above
► (b) Atoms are indivisible.
11. One atomic mass unit is a mass unit equal to exactly one twelfth (1/12th) the mass of one atom of ___________.
(a) Carbon-12
(b) Nitrogen -14
(c) Carbon-1
(d) Silicon-14
► (a) Carbon-12
12. If all the reactants in a chemical reaction are completely used, which of the following statements accurately describes the relationship between the reactants and the products?
(a) The reactants must contain more complex molecules than the products do.
(b) The products must have different physical state than the reactants.
(c) The total mass of the reactants must equal the total mass of the products.
(d) The density of the reactants must equal the density of the products.
► (c) The total mass of the reactants must equal the total mass of the products.
13. One mole of molecules may not be equal to:
(a) 6.022 x 1023 number of molecules
(b) Given number of particles (N)
(c) Avogadro number
(d) Molecular mass in grams
► (b) Given number of particles (N)
14. 9 grams of water decompose to give:
(a) 4g oxygen and 16g hydrogen
(b) 2g hydrogen and 1g oxygen
(c) 8g oxygen and 1g hydrogen
(d) none
► (c) 8g oxygen and 1g hydrogen
15. Who gave the Law of constant proportions?
(a) Cavendish
(b) Proust
(c) Dalton
(d) Lavoisier
► (b) Proust
16. According to Law of conservation of mass, mass of reactants wil be equal to the mass of:
(a) Catalysts
(b) Products
(c) Apparatus used for reaction
(d) Gases evolved
► (b) Products
17. How do atoms usually exist in nature?
(a) In the form of molecules
(b) In the form of ions
(c) In the free state
(d) In the form of molecules and Ions
► (d) In the form of molecules and Ions
18. What is the mass of 0.5 mole of Hydrogen atom
(a) 2.0 g
(b) 1.5 g
(c) 1 g
(d) 0.5 g
► (d) 0.5 g
19. The number of atoms present in one molecule of an element is called as:
(a) Empirical formula
(b) Molecule
(c) Atomicity
(d) Compound
► (c) Atomicity
20. Calculate the formula unit mass of ZnCl2?
(a) 137 u
(b) 124 u
(c) 123 u
(d) 111 u
► (a) 137 u
21. Which of the following pair of elements represents a mole ratio of 1:1?
(a) 20 g of sodium and 20 g of calcium
(b) 7 g of nitrogen and 12 gm of sodium
(c) 10 g of calcium and 6 g of carbon
(d) 14 g of nitrogen and 24 g of magnesium
► (d) 14 g of nitrogen and 24 g of magnesium
22. Which of the following is the correct IUPAC symbol for the element Cobalt?
(a) Co
(b) Cb
(c) C
(d) none of these
► (a) Co
23. Which of the following can be used to see atoms?
(a) Scanning tunneling microscope
(b) Microscope
(c) Most powerful microscope
(d) Optical microscope
► (a) Scanning tunneling microscope
24. Which one of the following is the modern symbol of Gold?
(a) Gl
(b) Go
(c) Si
(d) Au
► (d) Au
25. NaCl molecule is made of which of the following ions?
(a) Na cation and Cl anion
(b) Cl cation and Na anion
(c) Both Na and Cl cation
(d) Both Na and Cl anion
► (a) Na cation and Cl anion
26. An atom has a mass number of 23 and atomic number 11. The number of protons are ________.
(a) 11
(b) 12
(c) 23
(d) 44
► (a) 11
27. The balancing of chemical equation is based upon:
(a) Law of conservation of mass
(b) Law of multiple proportions
(c) Law of definite proportion
(d) Law of combining volumes
► (a) Law of conservation of mass
28. The number of moles of oxygen atoms in two moles of nitric acid is:
(a) 2
(b) 4
(c) 8
(d) 6
► (d) 6
29. During a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is known as
(a) Law of conservation of mass
(b) Law of multiple proportion
(c) Law of constant proportion
(d) None of these
► (a) Law of conservation of mass
30. Who was the first to use the symbols for elements?
(a) Joseph L Proust
(b) Berzillius
(c) Antoine L Lavoisier
(d) Dalton
► (d) Dalton
31. Valency of Calcium element is:
(a) 4
(b) 5
(c) 2
(d) 3
► (c) 2
32. The mass of 0.5 moles of Water molecules is:(Atomic mass, H =1; O = 16)
(a) 27 g
(b) 0.5 g
(c) 9 g
(d) 18 g
► (c) 9 g
33. Who stated the Law of conservation of mass?
(a) Thomson
(b) Lavoisier
(c) Dalton
(d) Cavendish
► (b) Lavoisier
34. Which constituent of air is monoatomic?
(a) Argon
(b) Water vapour
(c) Oxygen
(d) Nitrogen
► (a) Argon
Question. An element X is tetravalent and another element Y is divalent. The compound formed by these two elements will be:
(a) XY
(b) XY2
(c) X2Y
(d) XY4
Answer : B
Question. Which of the following represents 12 u?
(a) Mass of 1 hydrogen atom
(b) Mass of C-12 atom
(c) Mass of 0-16 atom
(d) 1/12th of mass of C-12 atom
Answer : D
Question. The word “mole” was introduced around 1896 by:
(a) Wilhelm Ostwald
(b) John Dalton
(c) Avogadro
(d) Vergilius
Answer : A
Question. One gram of which of the following contains largest number of oxygen atoms?
(a) O
(b) O2
(c) O3
(d) All contains same
Answer : C
Question. Percentage of calcium in calcium carbonate is
(a) 40
(b) 30
(c) 48
(d) 36
Answer : A
Question. 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
Answer : C
Question. What is the formula mass unit of ZnO?
(a) 18 u
(b) 81 u
(c) 88 u
(d) 188 u
Answer : B
Question. Formula for Aluminium Oxide is:
(a) AlO
(b) AlO2
(c) Al3O2
(d) Al2O3
Answer : D
Question. How many molecules are present in one gram of hydrogen?
(a) 6.02 × 1023
(b) 3.01 × 1023
(c) 2.5 × 1023
(d) 1.5 × 1023
Answer : B
Question. The correct symbol for silver is:
(a) Ag
(b) S
(c) Ar
(d) AI
Answer : A
Question. 1 u or 1 amu means
(a) 1/12th mass of C-12 atoms
(b) Mass of C-12 atom
(c) Mass of O-16 atom
(d) Mass of Hydrogen molecule
Answer : A
Question. The chemical symbol for sodium is
(a) So
(b) Sd
(c) NA
(d) Na
Answer : D
Question. Who laid the foundation of laws of Chemical Combination:
(a) Democritus
(b) Lavoisier
(c) Dalton
(d) Proust
Answer : B
Question. The molecule having an atomicity of 4 is:
(a) Sulphate molecule
(b) Ozone molecule
(c) Phosphorus molecule
(d) Methane molecule
Answer : C
Question. The percentage of copper and oxygen in samples of CuO obtained by different methods were found to be the same. The illustrate the law of:
(a) Constant proportion
(b) Conservation of mass
(c) Multiple proportions
(d) Reciprocal proportions
Answer : A
Question:
a. 24g of Mg: 1 mole
b. 35.5g of Cl2: _________
a) 0.5mol
b) 1 mol
c) 2moles
d) 2.5 moles
Answer: 0.5mol
Question:
a. Oxygen: diatomic
b. Ozone :_______
a) Triatomic
b) Monoatomic
c) Diatomic
d) Tetra atomic
Answer: Triatomic
Question: The mass of a single atom of an element X is 2.65X 10-23g. The atomic mass and name of the element is:
a) 16u, oxygen
b) 16u, Sulphur
c) 32u, oxygen
d) 32u, Sulphur
Answer: 16u, oxygen
Question: An element X has valency equal to 3. What will be its formula with carbonate ions?
a) X2(CO3)3
b) X2CO3
c) XCO3
d) X(CO3)3
Answer: X2(CO3)3
Question: Which of the following has the smallest number of molecules?
a) 0.1 moles of CO2
b) 3.4g of NH3
c) 2g of H2 at STP
d) 16g of O2 gas
Answer: 0.1 moles of CO2
Question: 16g of S8 contains:
a) 6.023x1023/16 atoms of S
b) 6.023x1023 Atoms of S
c) 6.023x1023/8 atoms of s
d) 6.023x1023/2 atoms of S
Answer: 6.023x1023/16 atoms of S
Question: The number of atoms present in 0.5 moles of Nitrogen atoms is same as in:
a) 8 g of O
b) 12 g of C
c) 24 g of Mg
d) 32 g of S
Answer: 8 g of O
Question: Out of 1 g of oxygen gas, 1 g of oxygen atoms and 1g of ozone , maximum number of atoms are present in:
a) All have equal number of atoms
b) 1g of oxygen gas
c) 1g of oxygen atoms
d) 1 g of ozone
Answer: All have equal number of atoms
Question: Arrange the following in increasing number of molecules:
i. 0.5moles of H2
ii. 4g of H2
iii. 18g of H2O
iv. 2.2g of CO2
a) iv < i < iii < ii
b) i < iii < iv < ii
c) iv < iii < ii < i
d) i < ii < iii < iv
Answer: iv < i < iii < ii
Question: How many moles of electrons weigh 1 kg. Mass of an electron is 9.1X10-31
a) 108/9.1X6.022
b) 6.022X1023
c) 6.022X1023/9.1X10-31
d) 1X1031/9.1
Answer: A
Question: Molecular weight of CuSO4.5H2O is equal to:
a) 249.5
b) 159.5
c) 159.5 X90
d) 159.5 +10 + 16
Answer: A
Question: The formula of Calcium phosphate is:
a) Ca3(PO4)2
b) CaPO4
c) Ca(PO4)2
d) Ca2(PO4)3
Answer: A
Question: Which of the following is a correct statement:
a) Na2S is sodium sulphide, Na2SO3 is sodium sulphite, Na2SO4 is sodium sulphate
b) Na2S is sodium sulphite, Na2SO3 is sodium sulphide, Na2SO4 is sodium sulphate
c) Na2S is sodium sulphide, Na2SO3 is sodium sulphate, Na2SO4 is sodium sulphite
d) Na2S is sodium sulphite, Na2SO3 is sodium sulphite, Na2SO4 is sodium sulphide
Answer: Na2S is sodium sulphide, Na2SO3 is sodium sulphite, Na2SO4 is sodium sulphate
Question: The balancing of chemical equations is in accordance with:
a) Both b and c
b) Law of combining volumes
c) Law of constant proportions
d) Law of conservation of mass
Answer: A
Question: 18g of water is electrolyse The weight of oxygen obtained is:
a) 16g
b) 8g
c) 4g
d) 1g
Answer: A
Question: Which is not represented by 1mole of Nitrogen gas?
a) 6.023X1023 atoms of N2
b) 6.023X1023 molecules of N2
c) 12.046 X1023 atoms of N2
d) 28g of N2
Answer: A
Question: The combining capacity of an element is called
a) Valency
b) Atomicity
c) Atomic number
d) Valence electrons
Answer: A
Question: Identify the correct symbol of gold:
a) Au
b) Go
c) Ge
d) Gd
Answer: A
Question: If isotopic distribution of C-12 & C-14 is 98% and 2% respectively, then number of C-14 atoms in 12 g of C is:
a) 1.244X1022
b) 1.244X1023
c) 3.88X1022
d) 3.88X1022
Answer: A
Question. Which of the following contains maximum number of molecules?
(a) 19 CO2
(b) 1 g N2
(c) 1 g H2
(d) 1 g CH4
Answer : C
Question. The molecular formula of potassium nitrate is ________.
(a) KNO3
(b) KNO
(c) KNO2
(d) KON
Answer : A
Question. What is the latin name of sodium?
(a) Kalium
(b) Plumbum
(c) Natrium
(d) None of the above
Answer : C
Question. The combining capacity of an element is called
(a) Valency
(b) Atomicity
(c) Atomic number
(d) Valence electron
Answer : A
Question. 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.
Answer : D
Question. The law of definite proportions was given by:
(a) John Dalton
(b) Humphry davy
(c) Proust
(d) Michael Faraday
Answer : C
Question. The most remarkable concept that Dalton’s atomic theory proposed was that of the:
(a) atomic weight
(b) atomic mass
(c) molar mass
(d) none of the above
Answer : B
Question. Who coined the term ‘Parmanu’ for the smallest indivisible particles?
(a) Leucippus
(b) L. Lavoisier
(c) Kanad
(d) None of them
Answer : C
Question. Identify the correct symbol of Gold.
(a) Go
(b) Gd
(c) Ge
(d) Au
Answer : D
Question. Which one of the following phrases would be incorrect to use?
(a) A mole of an element
(b) A mole of a compound
(c) An atom of an element
(d) An atom of a compound
Answer : D
Question. The chemical symbol for barium is:
(a) B
(b) Ba
(c) Be
(d) Bi
Answer : B
Question. The molecular formula of potassium nitrate is ________.
(a) KNO3
(b) KNO
(c) KNO2
(d) KO
Answer : A
Question. The atomic mass of carbon is:
(a) 12
(b) 14
(c) 16
(d) 23
Answer : A
Question. Who coined the term ‘Parmanu’ for the smallest indivisible particles?
(a) Leucippus
(b) L. Lavoisier
(c) Kanad
(d) None of them
Answer : C
Question. The mass of sodium in 11.7 g of sodium chloride is:
(a) 2.3g
(b) 4.6g
(c) 6.9g
(d) 7.1g
Answer : B
Atoms and Molecules class 9 chemistry MCQ & SAQ
Q1. Define the law of conservation of mass.
In a chemical reaction mass can neither be created nor destroyed.
E.g., 2Na + Cl2 ——–> 2NaCl
2 x 23 + 2 x 35.5 ——> 2(23 + 35.5)
Q2. Explain the law of constant proportion.
In a chemical substance, the elements are always present in definite proportions by mass.
Example: In nitric oxide, the ratio of the mass of nitrogen to the mass of oxygen N: O is always 1:1.
Q3. Who coined the term atom?
John Dalton coined the term atom.
Q4. Define atom.
The smallest particle of matter, which can take part in a chemical reaction is called an atom.
Q5. Define molecules.
The smallest particle of an element or compound which can exist independently is called a molecule.
Q6. Define atomicity.
The number of atoms constituting a molecule is known as its atomicity.
Q7. What is an atomic mass unit?
The sum of the atomic masses of all the atoms in a molecule of the substance is expressed in the atomic mass unit. E.g., H20 = 1 x 2 + 16 = 18 amu
Q8. How do atoms exist?
Atoms exist in the form of atoms, molecules or ions.
Q9. Give the atomicity of phosphorus and nitrogen.
The atomicity of phosphorus is P4 i.e., 4.
The atomicity of nitrogen is N2 i.e., 2.
Q10. What is an ion?
Charged atom is called an ion. The ion can be positively charged called cation or negatively charged called anion.
Q11. Give one example of cation and anion.
Cation => Na+
Anion => Cl–
Q12. Give one difference between cation and anion.
Cations are positively charged ion.
Anions are negatively charged ion.
Q13. Give the chemical formula for ammonium sulphate.
Ammonium sulphate
NH4+ SO42-
Chemical formula —-> (NH4)2S04.
Q14. What is Avogadro’s constant?
Avogadro's constant (6.022 x 1023) is defined as the number of atoms that are present in exactly 12 g of carbon-12.
Q15. Find the molecular mass of H20.
Molecular mass of H20
= (2 x 1) + (16)
= 2 + 16 = 18 u
Short Answer Type Questions
Q1. Give the unit to measure the size of an atom and give the size of a hydrogen atom.
The unit to measure the size of an atom is nanometer, and the size of a hydrogen atom is 10-10m.
Q2. What is IUPAC, give its one function?
IUPAC is International Union for Pure and Applied Chemistry. It approves the names of elements.
Q3. Give the Latin name for sodium, potassium, gold and mercury.
Sodium —> Natrium, Gold —> Aurum
Potassium —> Kalium, Mercury —> Hydrargyrum
Q4. What is the ratio by mass of combining elements in H2O, CO2 and NH3?
H2O ratio by mass of combining elements 2: 16 —>1: 8 (H: O)
CO2 ratio by mass of combining elements 12: 32—> 3: 08 (C: O)
NH3 ratio by mass of combining elements 14 : 3—>14 : 3 (N: H)
Q5. Define valency and give the valency for the following elements:
Magnesium, Aluminium, Chlorine and Copper.
Valency: The combining capacity of an element is called its valency. Valency of the following elements:
Magnesium – 2
Aluminium – 3
Chlorine – 1
Copper – 2
Q6. What is a polyatomic ion? Give one example.
A group of atoms carrying a charge is known as a polyatomic ion.
E.g., Ammonium – NH4+
Nitrate – N03–
Q7. Write down the formula for:
Copper nitrate, calcium sulphate and aluminium hydroxide.
Chemical formula:
Copper nitrate —> Cu(N03)2
Calcium sulphate —> CaS04
Aluminium hydroxide —> Al(OH)3
Q8. What is formula unit mass? How is it different from molecular mass?
The formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound. The constituent particles of formula unit mass are ions and the constituent particles of molecular mass are atoms.
Q9. Find the number of moles in the following:
(i) 50 g of H2O
(ii) 7 g of Na
Number of moles in
(i) Molar mass of H2O = 18 g
Given mass of H2O = 50 g
Q10. Find the number of atoms in the following:
(i) 0.5 mole of C atom
(ii) 2 mole of N atom
(i) 0.5 mole of C atom:
Number of atoms in 1 mole of C atom = 6.022 x 1023 atoms
Number of atoms in 0.5 mole of C atom = 6.022 x 1023 x 0.5
= 3.011 x 1023 atoms
(ii) 2 mole of N atom:
Number of atoms in 1 mole of N atom = 6.022 x 1023 atoms
Number of atoms in 2 mole of N atom = 6.022 x 2 x 1023
= 1.2044 x 1024 atoms
Q11. Find the mass of the following:
(i) 6.022 x 1023 number of O2 molecules
(ii) 1.5 mole of CO2 molecule
(i) 6.022 x 1023 number of 02 molecules:
Mass of 1 mole of O2 molecule = 6.022 x 1023 molecules = 32 g
(ii) 1.5 mole of CO2 molecule:
Mass of 1 mole of C02 molecule = 6.022 x 1023 molecules = 44 g
Mass of 1.5 mole C02 molecule = 44 x 1.5 = 66 g
Q12. Show the relationship between a mole, Avogadro number and mass.
Q13. What are the rules for writing the symbol of an element?
IUPAC —> International Union of Pure and Applied Chemistry approves name of elements.
Symbols are the first one or two letters of the element’s name in English. The first letter of a symbol is always written as a capital letter (upper case) and the second letter as a small letter (lower case).
e.g., Hydrogen —> H Helium —> He
Some symbols are taken from the names of elements in Latin, German or Greek.
e.g., Symbol of iron is Fe, its Latin name is Ferrum.
The symbol of sodium is Na, its Latin name is Natrium.
Q14. Explain relative atomic mass and relative molecular mass.
Relative atomic mass: It can be defined as the number of times one atom of a given element is heavier than 1/12 th of the mass of an atom of carbon-12. Relative Molecular Mass: It is defined as the number of times one molecule
of a substance or given element is heavier than 1/12 th of the mass of one atom of carbon-12.
Q15. The formula of carbon dioxide is CO2. What information do you get from this formula?
(i) CO2 represents carbon-dioxide.
(ii) CO2 is one molecule of carbon dioxide.
(iii) CO2 is one mole of carbon dioxide i.e., it contains 6.022 x 1023 molecules of carbon dioxide.
(iv) CO2 contains 1 atom of carbon and two atoms of oxygen.
(v) CO2 represents 44 g of molar mass.
Q16. State 3 points of difference between an atom and an ion.
Q17. Calculate the formula unit mass of NaCl and CaCl2.
(Na = 23, Cl = 35.5, Ca = 40)
Formula unit mass of NaCl = 23 + 35.5
= 58.5 u
Formula unit mass of CaCl2 = 40 + (2 x 35.5)
= 40 + 71 = 111 u
Q18. The ratio by mass for hydrogen and oxygen in water is given as 1 : 8 respectively. Calculate the ratio by number of atoms for a water molecule.
The ratio by the number of atoms for a water molecule are:
Thus, the ratio by the number of atoms for water is H: O = 2: 1.
Q19. Write down the chemical formula for the following compounds:
(a) Aluminium carbonate
(b) Calcium sulphide
(c) Zinc carbonate
(d) Copper phosphate
(e) Magnesium bicarbonate
(f) Aluminium hydroxide.
The chemical formula are:
Q20. Give the atomicity of the following compounds:
(a) Ca(OH)2 (d) H2S04
(b) Mg(HC03)2 (e) Al2(S04)3
(c) Cu20. (f) MgCl2
The atomicity of the molecules are:
Q21. Explain the difference between 20, 02 and 03.
2O —> It represents 2 atoms of oxygen (cannot exist independently).
O2 —> It represents one molecule of oxygen (made up of 2 atoms) that can exist freely.
O3 —> It represents one molecule of ozone (made up of 3 atoms) it can exist independently.
Atoms and Molecules class 9 chemistry MCQ & SAQ
Q1. (a) How do atoms exist?
(b) What is atomicity?
(c) What are polyatomic ions?
(a) Atoms of some elements are not able to exist independently. For such elements, atoms form molecules and ions. In the case of metals and inert gases, atoms can exist independently.
(b) The number of atoms constituting a molecule is known as its atomicity.
E.g., O3 —> atomicity is 3
O2 —> atomicity is 2
(c) Polyatomic ions: When more than two atoms combine together and act like an atom with a charge on it is called a polyatomic ion.
E.g., OH–, N03–, NH4+
Q2. Calculate
(a) the mass of one atom of oxygen
(b) the mass of one molecule of oxygen
(c) the mass of one mole of oxygen gas
(d) the mass of one ion of oxygen
(e) the number of atoms in 1 mole of oxygen molecule
(a) Mass of one atom of oxygen
1 mole of oxygen atom = 16 gm = 6.022 x 1023 atoms.
∴ Mass of one atom of oxygen = 16/6.022 x 1023 = 2.65 x 1023
(b) Mass of one molecule of oxygen
1 molecule of oxygen = O2
= 2 x 16
= 32 u
(c) Mass of one oxygen gas
1 molecule of oxygen gas is O2 = 32 u
(d) Mass of one ion of oxygen
One mole of oxygen = 6.022 x 1023 atoms = 16g. 16
Mass of one ion of oxygen = 16/6.022 x 1023
= 2.65 x 1023
(e) Number of atoms in one mole of oxygen molecule 1 mole of oxygen molecule i.e.
02 = 6.022 x 1023 molecules.
1 molecule of 02 = 2 atoms.
∴ Number of atoms in 1 mole of oxygen molecule = 6.022 x 1023 x 2 atoms
= 1.2044 x 1024 atoms
Q3. What is meant by atomic mass, the gram atomic mass of an element? Why is the mass have different expressions i.e., ‘u’ and ‘g’?
The atoms are very tiny and their individual mass cannot be calculated as it is negligible. Hence the mass of atoms is expressed in units with respect to a fixed standard. Initially, a hydrogen atom with mass 1 was taken as a standard unit by Dalton. Later, it was replaced by an oxygen atom (0=16). But due to the isotopes, the masses were found in fractions instead of the whole number. Hence, carbon (C=12) isotope was taken as a standard unit and was universally accepted.
The atomic mass unit is equal to one-twelfth (1/12) the mass of an atom of carbon-12, its unit is u.
Gramatomic mass: When the atomic mass of an element is expressed in grams, it is called the gram atomic mass of the element.
The mass of atoms, molecules are expressed in ‘u’ and the mass of moles i.e., the molar mass is expressed in g.
Q4. Define a mole. Give the significance of the mole.
Mole-One mole of any species (atoms, molecules, ions or particles) is that quantity or number having a mass equal to its atomic or molecular mass in grams.
1 mole = 6.022 x 1023 in number (atoms, molecules, ions or particles)
Significance of the mole
1. A mole gives the number of entities present i.e, 6.022 x 1023 particles of the substance.
2. Mass of 1 mole is expressed as M grams.
3. Mass of 1 mole = mass of 6.022 x 1023 atoms of the element.
E.g., 1 mole of O2 = 6.022 x 1023 atoms
2 x 16 = 32 g
6.022 x 2 x 1023 = 1.2044 x 104 atoms
1 mole of (compound) HCl = 6.022 x x 1023 atoms of H and Cl atoms
(1 + 35.5 = 36.5 g) (6.022 x 1023 molecules of HC1).
Comments
Post a Comment