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Chemistry Test - 14

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Chemistry Test - 14
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  • Question 1
    1 / -0

    In a sample of ethyl ethanoate\(\left(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}\right)\)the two oxygen atoms have the same number of electrons but differentnumber of neutrons. Which of the following is the correct reason for it?

    Solution

    The two oxygen \(\mathrm{(O)}\) atoms in \(\left(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}\right)\)are isotopes.

    The two \(\mathrm{(O)}\)-atoms in\(\left(\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}\right)\)can have different number of neutrons only if the two \(\mathrm{(O)}\)-atoms are isotopes. It is because, isotopes of an element have same number of protons (and electrons) but different number of neutrons.

  • Question 2
    1 / -0

    Which of the following pollutant is a component of Acid rains?

    Solution

    Acid rain: Acid rain is a by-product of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere.

    Burning of fossil fuels (which contain sulphur and nitrogenous matter) such as coal and oil in power stations and furnaces or petrol and diesel in motor engines produce sulphur dioxide and nitrogen oxides. SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain.

    2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)

    4NO2 (g) + O2 (g) + 2H2O (l) → 4HNO3 (aq)

    So, the correct option is HNO3.

  • Question 3
    1 / -0

    According to VSEPR theory, the respective shapes of PCl5 and ICl5 should be

    Solution

    The molecular geometry of PCl5 is trigonal bipyramid with symmetric electron region distribution around the central atom.

    These are arranged in a trigonal bipyramidal shape with a 175° F(axial)-Cl-F(axial) bond angle. The two lone pairs take equatorial positions because they demand more space than the bonds. The result is a T-shaped molecule.

  • Question 4
    1 / -0

    Consider the reaction, CH3CH2CH2Br + NaCN→ CH3CH2CH2CN +NaBr.This reaction will be the fastest in:

    Solution

    The solvent affects the rate of reaction because solvents may or may not surround a nucleophile, thus hindering or not hindering its approach to the carbon atom. Polar aprotic solvents, like tetrahydrofuran, are better solvents for this reaction than polar protic solvents because polar protic solvents will hydrogen bond to the nucleophile, hindering it from attacking the carbon with the leaving group. A polar aprotic solvent with a low dielectric constant or a hindered dipole end will favor SN2manner of nucleophilic substitution reaction. Examples: DMSO, DMF, acetone etc. In polar aprotic solvent, nucleophilicity parallels basicity.

  • Question 5
    1 / -0

    What is the packing fraction of \(_{26}^{56} \mathrm{Fe}\)?

    (Isotopic mass \(=55.92066\))

    Solution

    Given that:

    Isotopic mass \(=55.92066\)

    Mass number\(=56\)

    We know that:

    Packing fraction \(=\frac{\text { Isotopic mass - Mass number }}{\text { Mass number }} \times 10^{4}\)

    \(=\frac{55.92066-56}{56} \times 10^{4}\)

    \(=-14.167\)

  • Question 6
    1 / -0

    The atomic number of an element is \(32\) and mass number \(55\). Calculate the number of neutrons?

    Solution

    Given:

    Atomic number or number of protons \(=32\)

    Mass number \(=55\)

    We know that,

    Mass number \((\mathrm{A})=\) Number of protons \(+\) Number of neutrons

    \(\Rightarrow55=32+\) Number of neutrons

    Number of neutrons \(=55-32\)

    Number of neutrons \(=23\)

  • Question 7
    1 / -0

    The plastic used to preserve yoghurts is replaced with a polymer called polylactic acid is an example of _______.

    Solution

    The plastic used to preserve yoghurts is replaced with a polymer called polylactic acid is an example of green chemistry.

    Since the usage of petroleum-based plastic is harmful to the environment, a polymer called polylactic acid, made using micro-organisms to convert cornstarch into a resin, is used to preserve yoghurt. The resulting polymer is used to replace rigid petroleum-based plastic used in yoghurt containers and water bottles and is environment-friendly. It is an application of green chemistry.

  • Question 8
    1 / -0

    Identify the product for the following reaction.

    \({CH} \equiv {CH}+{HOCl} \rightarrow\)

    Solution

    \({HOCl} \longrightarrow {OH}^{-}+{Cl}^{+}\)

    \(C l^{+}\)shall attack acetylene as an electrophile and \(O H^{-}\)will end the addition with a nucleophilic addition.

    Therefore, the final reaction will be:

    \({CH} \equiv {CH}+2 {HOCl} \longrightarrow \underset{\text { Unstable }}{{CH}({OH})_{2}-{CHCl}_{2}} {\overset{-{H_2O}}{\longrightarrow} {CHCl}_{2}-{CHO}}\)

  • Question 9
    1 / -0

    Which of the following \(\mathrm{CH}_{3}-\mathrm{X}\) bond has the highest polarity?

    Solution

    Fluorine is the most electronegative element in the periodic table.

    All the given options belong to group 17 of the periodic table and are termed as 'Halogens'.

    As we move down in a group, the electronegativity decreases as the atomic size increases.

    As we move right in a period, the electronegativity increases (up to group 17), since the size of the atom decreases and the nuclear charge increases.

    The decreasing order of electronegativity : F > Cl > Br > I

    \(\mathrm{CH}_{3}-\mathrm{X}\) bond where \(\mathrm{X}\) is halogen

    The difference between Carbon and halogen bond electronegativity gives its polarity.

    The electronegativity of Halogens are:

    \(\begin{array}{|l|c|} \hline \text { Halogen } & \text { Electronegativity } \\ \hline \text { Fluorine } & 4.0 \\ \hline \text { Chlorine } & 3.0 \\ \hline \text { Bromine } & 2.8 \\ \hline \text { lodine } & 2.5 \\ \hline \end{array}\)

    The electronegativity of carbon is 2.5.

    Hence C-F bond is more polar as fluorine is the most electronegative.

    So, the difference in order,

    (C - F) > (C - Br) > (C - Cl) > (C - Br) > (C - I)

  • Question 10
    1 / -0

    In Hall's process, the ore is mixed with:

    Solution

    In Hall's process, the ore is mixed withSodium carbonate.

    Hall's process is used for the extraction of Aluminum from Alumina. Bauxite is concentrated through Hall’s process, in which sodium aluminate is prepared using sodium carbonate in bauxite. When excess carbon dioxide is passed through sodium aluminate in the presence of water, it forms aluminum hydroxide along with sodium carbonate. When dried aluminum hydroxide is ignited, alumina is formed.

    The reaction involved in Hall's process is as follows:

    \({Al}_{2} {O}_{3} .2 {H}_{2} {O}+2 {Na}_{2} {CO}_{3} \rightarrow 2 {NaAlO}_{2}+{CO}_{2}+2 {H}_{2} {O}\)

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