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Atoms And Molecules Test - 3

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Atoms And Molecules Test - 3
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  • Question 1
    1 / -0
    In a reaction, 32 g of sulphur reacts with a certain amount of oxygen to produce 64 g of sulphur dioxide. What is the amount of oxygen used in this reaction?
    Solution
    According to the law of conservation of mass:
    Total mass before the reaction = Total mass after the reaction



    32 + x = 64
    x = 32 g
  • Question 2
    1 / -0
    H2O, obtained from different sources, always contains hydrogen and oxygen atoms in the respective ratio of 2 : 1. This is in accordance with which of the following?
    Solution
    Law of definite proportions states that elements combine in a fixed proportion by mass to form compounds. Hence, the mass as well as the number of atoms of each element in the molecule of a compound is fixed.
  • Question 3
    1 / -0
    Which among the following illustrate the law of reciprocal proportions?
    Solution
    In CH4 and CO2, the masses of hydrogen and oxygen that react with 12 g of carbon are in respective ratios of 4 : 32 or 1 : 8.
    In H2O, ratio of mass of hydrogen to mass of oxygen = 1 : 8
    Hence, the law of reciprocal proportions is being illustrated by CH4, CO2 and H2O.
    H2O and H2O2 illustrate the law of multiple proportions.
    SO2 and SO3 also illustrate the law of multiple proportions.
  • Question 4
    1 / -0
    Nitrogen and oxygen form three oxides.

    In oxide I, 1.00 g of nitrogen combines with 0.57 g of oxygen.
    In oxide II, 2.00 g of nitrogen combines with 2.24 g of oxygen.
    In oxide III, 3.00 g of nitrogen combines with 5.11 g of oxygen.

    These results are in accordance with which of the following?
    Solution
    Compound Mass of nitrogen Mass of oxygen Mass of oxygen that reacts with 1 g of nitrogen Ratio of the mass of oxygen to the mass of oxygen that reacts with 1 g of nitrogen
    Oxide I 1 g 0.57 g 0.57 g 1
    Oxide II 2 g 2.24 g 1.12 g 1.96 ≈ 2
    Oxide III 3 g 5. 11 g 1.70 g 2.988 ≈ 3

    Hence, the data illustrates the law of multiple proportions.
  • Question 5
    1 / -0
    Nitrogen and hydrogen react to form ammonia, as shown below:

    N2 (g) + 3H2 (g) 2NH3 (g)

    The volume of hydrogen required to react completely with 10 L of N2 and the volume of NH3 produced, respectively, are
    Solution
    The balanced equation shows:
    n(N2) : n(H2) : n(NH3) = 1 : 3 : 2
    According to the Avogadro's law:
    Volume ratio = Molar ratio
    V(N2) : V(H2) : V(NH3) = 1 : 3 : 2
    Therefore, the volume of H2 required is 30 L and the volume of NH3 produced is 20 L.
  • Question 6
    1 / -0
    According to Dalton's theory, which of the following particles is indivisible and cannot be created or destroyed in a chemical reaction?
    Solution
    According to Dalton's theory, an atom is the constituent particle of all matter and cannot be created or destroyed during any physical or chemical change.
    The sub-atomic particles - electrons, protons and neutrons - were not known at the time when Dalton gave his theory.
  • Question 7
    1 / -0
    Which of the following statements contradict Dalton's atomic theory?

    (A) A chemical change involves rearrangement of atoms.
    (B) Atoms form ions by gain or loss of electrons.
    (C) The number of atoms may change when a substance changes from solid to gaseous state.
    (D) The total number of atoms during a chemical change remains unaltered.
    Solution
    Statement B contradicts Dalton's atomic theory because the theory proposes that atoms are indivisible and it does not talk of sub-atomic particles.
    Statement C contradicts Dalton's atomic theory, which states that atom is indestructible.
  • Question 8
    1 / -0
    Two elements, X and Y, have 5 and 7 valence electrons, respectively. What will be the most probable formula of the compound formed by them?
    Solution
    Both X and Y are non-metals and will associate through covalent bonds.
    X has 5 valence electrons and its valency is 3.
    Y has 7 valence electrons and its valency is 1.
    Therefore, the formula of the compound will be: XY3.
  • Question 9
    1 / -0
    The atomic numbers of four elements - A, B, C and D - are 6, 8, 10 and 12, respectively. The two elements which can react to form an ionic bond are
    Solution
    A (Z = 6) is carbon and its electronic configuration is: 2, 4.
    B (Z = 8) is oxygen and its electronic configuration is: 2, 6.
    C (Z = 10) is neon and its electronic configuration is: 2, 8.
    D (Z = 12) is magnesium and its electronic configuration is: 2, 8, 2.
    Magnesium is a metal and oxygen is a non-metal and they react to form an ionic oxide.
    Neon is a noble gas and does not react, whereas carbon forms covalent compounds.
  • Question 10
    1 / -0
    The gaseous hydrocarbon acetylene, C2H2, used in welder's torches, releases 1300 KJ when 1 mole of C2H2 undergoes combustion. Which of the following statements is not true?
    Solution
    Balanced chemical reaction: 2C2H2 + 5O2 → 4CO2 + 2H2O
    Hence, option (2) is incorrect.

    Since heat is liberated, the reaction is exothermic. Hence, option (1) is correct.
    It is evident from the balanced reaction that 2 moles of water are produced when 2 moles of acetylene react. Hence, option (3) is correct.
    It is also evident that the number of moles of CO2 produced is twice the number of moles of C2H2 reacted.
    Hence, combustion of 13 g (0.5 mole) of C2H2 would produce 44 g (1 mole) of CO2. Hence, option (4) is correct.
  • Question 11
    1 / -0
    Mass of sodium in 62 g of Na2O is 46 g and in 186 g of Na2O is 138 g. This data supports the law that was given by
    Solution
    The data indicates that the percentage of Na in Na2O is fixed, i.e. 74.19%, and supports the law of constant proportions given by Joseph Proust.
  • Question 12
    1 / -0
    If a solution of glucose is 18% by mass, the number of molecules of glucose contained in 1000 g of the solution is:
    Solution
    Mass of glucose in 1000 g of solution =

    Molar mass of glucose (C6H12O6) =

    Number of moles of glucose =

    Therefore, number of molecules of glucose =
  • Question 13
    1 / -0
    Which of the following will have the same empirical and molecular formulae?
    Solution
    Since the number of carbon, the number of hydrogen and the number of oxygen atoms in C3H8O are co-prime numbers, the empirical formula will be the same as the molecular formula.

    Molecular Formula Empirical Formula
    C3H8O C3H8O
    CH3COOH or C2H4O2 CH2O
    C6H12O6 CH2O
    H2O2 HO
  • Question 14
    1 / -0
    What is the mass of calcium in 250 g of calcium carbonate?
    [Atomic masses of Ca, C and O respectively are 40 u, 12 u and 16 u.]
    Solution
    Formula unit of calcium carbonate is CaCO3.

    Molecular mass = 40 + 12 + (3 16) = 100 u

    % of Ca =
    Therefore, mass of calcium in the given sample = 40% of 250 g =
  • Question 15
    1 / -0
    Identify the incorrect statement.
    Solution
    Mass of a carbon atom is 12 u because 1 u is of a carbon atom.
  • Question 16
    1 / -0
    What is the number of atoms present in 112 grams of N2?
    Solution
    Molar mass of N2 = 14 x 2 = 28 g
    Number of moles of N2 = = = 4
    Number of moles of N atoms = 2 x 4 = 8
    Number of N atoms = n x NA = 8 x 6.023 x 1023 = 48.184 x 1023 = 4.8184 x 1024
  • Question 17
    1 / -0
    At room temperature, the volume of a drop of water is 0.0018 ml. What is the number of water molecules present in it?
    Solution
    Density of H2O = 1 g ml-1
    Mass = Volume x Density = 0.0018 x 1 = 0.0018 g
    Number of moles of H2O = = 10-4
    Number of molecules of H2O = n x 6.023 x 1023 = 10-4 x 6.023 x 1023 = 6.023 x 1019
  • Question 18
    1 / -0
    What is the molecular formula of the compound whose molecular mass is 26 u and empirical formula is CH?
    Solution
    Empirical formula mass = 12 + 1 = 13 u
    Molecular mass = 26 u
    n = = 2
    Therefore, the molecular formula of the compound is C2H2.
  • Question 19
    1 / -0
    How many atoms of hydrogen are present in (NH4)2SO4 and NH4H2PO4, respectively?
    Solution
    Each formula unit of ammonium sulphate (NH4)2SO4 has 8 H atoms.
    Each formula unit of ammonium hydrophosphate NH4H2PO4 has 6 H atoms.
  • Question 20
    1 / -0
    The number of aluminium ions in one formula unit of aluminium sulphate is:
    Solution
    The chemical formula of aluminium sulphate is:

    It can be clearly inferred that each formula unit contains two aluminium ions (Al+3).
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