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Chemistry Test 129
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Chemistry Test 129
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  • Question 1/10
    4 / -1

    Two oxides of metal contain 27.6℅ and 30℅ oxygen respectively. If formula of first oxide is M3O4, then formula of second oxide is:

    Solutions

    Given that, formula of first oxide = M3O4

    Let mass of the metal = x

    % of metal in M3O4 = (3x / 3x + 64) * 100

    but as given % age = (100 - 27.6) = 72.4%

    so, (3x / 3x + 64) * 100 = 72.4

    or x = 56.

    in 2nd oxide,

    oxygen = 30%....so metal = 70%

    so, the ratio is

    M : O

    70 / 56 : 30 / 16

    1.25 : 1.875

    2 : 3

    so, 2nd oxide is M2O3

     

  • Question 2/10
    4 / -1

    5.6 litres of a gas at N.T.P. are found to have a mass of 11 g. The molecular mass of the gas is

    Solutions

    5.6lit = 11g

    22.4lit = ? (x) g

    x = 22.4 × 11 / 5.6

    x = 44g

    Thus, Molecular mass of gas is 44g

     

  • Question 3/10
    4 / -1

    The crystalline salt, Na2SO4xH2O on heating loses 55.9% of its weight. The formula of the crystalline salt is

    Solutions

    Molar mass of salt = (2 × 23) + 32 + (16 × 4) + x × 18

    = 142 + 18x

    On heating it will lose water and become anhydrous. 55.9% mass is the mass of water in Na2SO4.xH2O.

    Mass by mass% = (mass / molar mass of compound) × 100

    mass of water = 18x

    55.9 = (18x / 142 + 18x) × 100

    55.9(142 + 18x) = 1800x

    7937.8 + 1006.2x = 1800x

    x = 9.99

    x = 10 (approx.)

    So, the molecular formula of compound is Na2SO4.10H2O.

     

  • Question 4/10
    4 / -1

    0.5 g of a metal on oxidation gave 0.79 g of its oxide. The equivalent weight of the metal is (approximately)

    Solutions

     Given,

    Mass of metal = 0.5 g

    Mass of oxide = 0.79 g

    First we have to calculate the Mass of Oxygen in metal oxide.

    Mass of Oxygen = Mass of oxide - Mass of Metal = 0.79 - 0.5 = 0.29 g

    The equivalent weight of oxygen is 8 g/eq.

    0.29 g of oxygen combines with the 0.5 g of metal

    8 g of oxygen combines with  of metal.

    Therefore, the equivalent weight of metal is 13.793 g/eq.

     

  • Question 5/10
    4 / -1

    Air contains nearly 20% oxygen by volume. The volume of air needed for complete combustion of 100 cc of acetylene will be

    Solutions

    Equation

    2 C2H2 + 5O2 → 4CO2 + 2 H2O

    In this reaction, we can see that, 2 moles of C2H2reacts with 5 moles of O2​ 

    Or, 1 mole of ​C2H2 reacts with 5 / 2 moles of O2​

    Under standard conditions, we can say that:

    22.44 L of C2H2 reacts with (5 / 2) x 22.4 L moles of O2

    So, 100 cc of C2H2 will reacts with (5 / 2) x 100 cc = 250 cc of O2​ .

    But, since air contains 20 % of oxygen by volume, the amount of air needed to react with 100 cc of C2H2 will be = 250 x (100 / 20) = 1250 cc of air.

     

  • Question 6/10
    4 / -1

    A solution of 10 ml(M/10) FeSO4 was titrated with KMnO4 solution in acidic medium. The amount of KMnO4 used will be

    Solutions

    The equation of the Mn2+ in acidic medium  will be.

    MnO4- + 8H++ 5 Fe2+ → Mn2++ 5Fe3+ +4H2O.

    We can balance the reaction by using redox balancing of acid and base.

    So, we know from the equation that 5 moles of iron react to form 1 mole of Mn+2.

    Thus, we can say that (10*0.1) moles of iron will react with the (10*0.1/5) moles of Manganese ions, which will be 0.2 thus, 10ml volume of KMnO4 and 0.02M moles of KMnO4.  We will get the same result if we use M1V1 = M2V2 formulae.

     

  • Question 7/10
    4 / -1

    At S.T.P. the density of CCl4 vapour in g/L will be nearest to

    Solutions

    Molecular Weight of CCl₄ = 35.5 + 12 x 4 = 154

    1 mole CCl₄ vapour=154 g

    According to Avogadro’s hypothesis we know that the molar volume of a gas at STP is 22.4 litres

    = 154 / 22.4 = 6.87

     

  • Question 8/10
    4 / -1

    The law of multiple proportions was proposed by

    Solutions

    Dalton's law of multiple proportions is part of the basis for modern atomic theory, along with Joseph Proust's law of definite composition (which states that compounds are formed by defined mass ratios of reacting elements) and the law of conservation of mass that was proposed by Antoine Lavoisier.

     

  • Question 9/10
    4 / -1

    The anode rays were discovered by

    Solutions

    The discovery of protons can be attributed to Rutherford. In 1886 Goldstein discovered existence of positively charged rays in the discharge tube by using perforated cathode. These rays were named as anode rays or cannal rays.

     

  • Question 10/10
    4 / -1

    Which of the following transitions of electrons in the hydrogen, atom will emit maximum energy ?

    Solutions

    Energy is given by formula

    E = hc / λ

    1 / λ = RZ2 [ 1 / n21 - 1 / n22 ]

    E = RZ2 hc [ 1 / n21 - 1 / n22]

    This energy will be highest when the transition is from n3 → n2.

     

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