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Chemistry Test - 15

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Chemistry Test - 15
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  • Question 1
    1 / -0

    The number of electrons in an element \(\mathrm{X}\) is \(15\) and the number of neutrons is \(16\). Which of the following is the correct representation of the element?

    Solution

    Given:

    Number of electrons in element \(\mathrm{X} = 15\) and number of neutrons \(= 16\)

    We know that,

    \({ }_{\mathrm{Z}}^{\mathrm{A}} \mathrm{X}\), where A stands for the atomic mass number which is the sum of protons and neutrons in the atom of an element and \(Z\) stands for an atomic number of the element which is the number of electrons in an atom of an element.

    Atomic mass \(=\) Number of electrons \(+\) Number of neutrons

    Atomic number \(=\) Number of protons \(=\) Number of electrons

    Therefore, atomic number is \(=15\) and atomic mass \(=15+16=31\).Thus, the atom is represented as\({ }_{15}^{31} \mathrm{X}\).

  • Question 2
    1 / -0

    In a chemical equilibrium \(\mathrm {a+b}\) give rise to \(\mathrm {c+d}\) when \(1\) mole each of the two reactants are mixed \(0.4\) mole each of the products are formed. The equilibrium constant is:

    Solution

    Given:

    In a chemical equilibrium \(\mathrm{a}+\mathrm{b}=\mathrm{c}+\mathrm{d}\) when one mole each of the two reactant are mixed \(0.4\) moles each of the product are formed

    From given, we have,

    A chemical equilibrium

    \(\mathrm {a+b=c+d}\)

    The equilibrium constant,

    \(\mathrm{Kc}=\frac {[\mathrm{c}][\mathrm{d}]}{[\mathrm{a}][\mathrm{b}]}\)

    When one mole each of the two reactants are mixed \(0.4\) moles each of theproduct is formed

    \(1\) mole \(=x\) reactants \(+0.4\) products

    \(1\) mole \(-0.4\) products \(=x\) reactants

    \(x\) reactants \(=0.6\) moles

    Therefore, when \([\mathrm{c}]=[\mathrm{d}]=0.4\) moles

    \([a]=[b]=0.6\) moles

    Therefore, the equilibrium constant,

    \(\mathrm{Kc}=\frac {(0.4 \times 0.4)}{(0.6 \times 0.6)}\)

    \(\mathrm{Kc}= \frac {4}{9}\)

    Therefore, the equilibrium constant \(\mathrm{Kc}= \frac {4}{9}\)

  • Question 3
    1 / -0

    If \(36.0 \mathrm{~g}\) of glucose is present in \(400 \mathrm{ml}\) of solution, molarity of the solution is:

    Solution

    Given,

    Mass of solute \(=36 \mathrm{~g}\)

    Volume of solution \(=400 \mathrm{ml}=0.4 \mathrm{~L}\)

    The molecular weight of glucose \(=180 \mathrm{gm}\)

    Molarity \(=\frac{\text { No of moles }}{\text { Volume(in L) }}\)

    \(=\frac{36}{180 \times 0.4}\)

    \(=0.5 \mathrm{M}\)

  • Question 4
    1 / -0

    The hydrocarbon that cannot be prepared effectively by the Wurtz reaction is:

    Solution

    Wurtz reaction is a suitable method for the preparation of symmetrical alkanes only.

    1,3-Dipropylcyclopentane can be obtained when a mixture of alkyl halides is used in the Wurtz reaction, and as a result, a mixture of products will be obtained.

    So, the Wurtz reaction will not give a good yield of the product.

  • Question 5
    1 / -0

    What is packing efficiency in simple cubic lattice?

    Solution

    Let the edge length or side of the cube be 'a', and the radius of each particle be 'r'.

    Then, we know that:

    For simple cubic lattice:

    \({a}=2 {r}\)

    Volume of cube \(=a^{3}\)

    \( =8 {r}^{3}\)

    In simple cube, each unit cell has only one sphere,

    Volume of sphere \(=\frac{4}{3} \pi {r}^{3}\)

    Packing efficiency \(=\frac{\text { Volume of a sphere }}{\text { Volume of the cube }} \times 100 \%\)

    \(=\frac{\frac{4}{3} \pi r^{3}}{8 r^{3}} \times 100\)

    \(=52.4 \%\)

  • Question 6
    1 / -0

    In which of the following species only one type of hybridization is present?

    Solution

    (A): \(\underset{\mathrm{sp}^{3}}{\mathrm{CH}_{3}}-\underset{\mathrm{sp}^{3}}{\mathrm{CH}_{2}}-\underset{\mathrm{sp}^{2}}{\mathrm{CH}_{2}}=\underset{\mathrm{sp}^{2}}{\mathrm{CH}_{2}}\)

    (B): \(\underset{\mathrm{sp}^{3}}{\mathrm{CH}_{3}}-\underset{\mathrm{sp}^{2}}{\mathrm{CH}}=\underset{\mathrm{sp}^{2}}{\mathrm{CH}}-\underset{\mathrm{sp}^{2}}{\mathrm{CH}_{2}^{+}}\)

    (C): \(\underset{\mathrm{sp}^{2}}{\mathrm{CH}_{2}}=\underset{\mathrm{sp}^{2}}{\mathrm{CH}}-\underset{\mathrm{sp}^{2}}{\mathrm{CH}}=\underset{\mathrm{sp}^{2}}{\mathrm{CH}_{2}}\)

    (D): \(\underset{\mathrm{sp}^{3}}{\mathrm{CH}_{3}}-\underset{\mathrm{sp}^{2}}{\mathrm{CH}}=\underset{\mathrm{sp}^{2}}{\mathrm{CH}}-\underset{\mathrm{sp}^{3}}{\mathrm{CH}_{2}^{-}}\)

    In 1,3 butadiene, \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}_{2}\), only one type ofhybridisation is present.

    As all the \(\mathrm{C}\) atoms are \(\mathrm{sp}^{2}\) hybridized as each \(\mathrm{C}\) isattached to a double bond.

    In all other options, different hybridized carbon atoms are present.

  • Question 7
    1 / -0

    The number of valence electrons ___________ across a period and ________ down the group:

    Solution

    The number of valence electrons increase across a period and remains same down the group.

    There are seven periods numbered as 1, 2, 3, 4, 5, 6 and 7. Each period consists of a series of elements having same valence shell. Each period corresponds to a number of shells. There are eighteen groups numbered as 1, 2, 3, 4, 5, ........... 13, 14, 15, 16, 17, 18. Group consists of a series of elements having similar valence shell electronic configuration. Across a period the valence electrons increases, while down a group they remain same.

  • Question 8
    1 / -0

    During discharging of a lead storage battery, which of the following is/are true?

    Solution

    Oxidation at anode is represented by the half cell reaction:

    \(\mathrm{Pb}(s)+\mathrm{SO}_{4}^{2-}(a q) \rightarrow \mathrm{PbSO}_{4}(s)+2 e^{-}\)

    Reduction at cathode is represented by the half cell reaction:

    \(\mathrm{PbO}_{2}(s)+4 H^{+}(a q)+S O_{4}^{2-}(a q)+2 e^{-} \rightarrow P b S O_{4}(s)+2 H_{2} O(l)\)

    The overall cell reaction is:

    \(\mathrm{Pb}(s)+\mathrm{PbO}_{2}(s)+2 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow 2 \mathrm{PbSO}_{4}(s)+2 \mathrm{H}_{2} \mathrm{O}(l)\)

    During discharging of a lead storage battery, sulfuric acid is consumed and water is produced.

    Lead sulphate is formed at both electrodes.

    Since sulfuric acid is consumed, the density of the electrolytic solution decreases.

  • Question 9
    1 / -0

    The diagram given below is a vapour pressure composition diagram for a binary solution of A and B. In the solution, A-B interactions are:

    Solution

    The vapour pressure of the solutions is almost equal to the vapour pressure of the initial A-A and B-B interactions.

    Hence, there is no deviation, neither positive nor negative.

    Therefore, A-B intersections are similar to the A-A and B-B interactions.

  • Question 10
    1 / -0

    During the isothermal expansion of an ideal gas, its:

    Solution

    During the isothermal expansion of an ideal gas, itsenthalpy remains unaffected.

    An isothermal process is a change of a system, in which the temperature remains constant. For an ideal gas during an isothermal expansion the enthalpy, as well as internal energy, remains constant.

    During isothermal expansion of an ideal gas, \(\Delta \mathrm{E}=0, \Delta \mathrm{T}=0\)

    From the definition of enthalpy,

    \(\mathrm{H}=\mathrm{E}+\mathrm{PV}\)

    or \(\Delta \mathrm{H}=\Delta \mathrm{E}+\Delta(\mathrm{PV})\)

    or \(\Delta \mathrm{H}=\Delta \mathrm{E}+\Delta(\mathrm{nRT})\{\) Since, \(\mathrm{PV=nRT}\) for an ideal gas \(\}\)

    or \(\Delta \mathrm{H}=\Delta \mathrm{E}+\mathrm{nR} \Delta \mathrm{T}\)

    or \(\Delta \mathrm{H}=0\)

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