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IIT JEE 2018: Ozone, structure, property and Important question

Jan 3, 2018 17:49 IST
    JEE 2018: Ozone
    JEE 2018: Ozone

    Ozone is a triatomic allotropic type of oxygen that is unsteady. It is available in the climate for around 20 kilometers (12-15 miles) above ocean level. Ozone is the allotrope of oxygen. In atmosphere ozone is present in the form of ozone layer.

    In atmosphere ozone formed by the help of reaction of oxygen with UV rays of sunlight.

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    Structure of ozone:

    The ozone atom is symmetrical and having a bond angle of 1170

    JEE Ozone Concepts 1

    The bond length between central oxygen and other two are identical

    JEE Ozone Concepts 1

    Ozone is a diamagnetic and “V” shape structure

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    Preparation:

    In lab ozone is prepared by the help of electrolysis of oxygen (silent electric discharge). This process is the Endothermic process

    The name of ozonizers for the same is as follow:

    • Brodie ozonizer OR
    • Siemens ozonizer OR
    • Siemens’ and Halske Ozonizer

    After reaction of Fluorine and cold water, mixture of oxygen and ozone are formed. In this mixture ozone percentage is 5% to 10%. This mixture is known as OZONIDE OXYGEN

    For the extraction of ozone from ozonide oxygen, this mixture is passed through spiral tube cooled by liquid air.

    In this tube ozone (O3) is liquefied at -112C and oxygen liquefied at -183C

    Properties:

    1. Ozone is a pale blue colour gas heavier than air
    2. Ozone is soluble in CCl4, Glacial CH3COOH, Turpentine oil OR oil of cinnamon
    3. Ozone gives brown colour solution with alcoholic bezidine solution
    4. Ozone gives violet colour with Tetramethyllead

    Oxidizing properties:

    1. Oxidation of PbS into PbSO4:

          PbS       +      4O3       →        PbSO4        +    4O2

        (Black Colour)                               (White Colour)

    Variation of colour in above reaction is an important point

    2. Oxidation of KI(neutral)

     

          KI          +      O3       →                   I2

           (Neutral)                 

    3. Oxidation of KI(neutral)

     

          KI          +      O3            →                    KIO3   +     KIO4

         (Alkaline)

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    In above reaction the oxidation state of   Iodine changes from -1 to zero, +5 and +7. It is very important point from the exam point of view

    1. Oxidation of moist Iodine

     

          I2          +      O3            →                     HIO3          -------V.V.Impotant

          (Moist)

    2. Oxidation of dry Iodine

     

          I2          +      O3         →                        I4O9          -------V.V.Impotant

         (Dry)                                                               Tetraiodine nonoxide

    3. Oxidation of Hg

     

    2Hg     +   O3            →                        Hg2O        + O2

    Bleaching Action of Ozone:

    O3 bleaches oil, starch and wood pulp

    Reducing property of Ozone:

    Ag2O           +     O3             →                         2O2      +      2Ag

    In Ozone, Colour of Ag becomes BLACK

    Some important solved questions are given below:

    Question 1:

    Which of the following is the wrong statement?                       [JEE Main 2013]                  

    (a)  ONCl and ONO are not isoelectronic

    (b)  03 molecule is bent

    (c)  Ozone is violet-black in solid state

    (d) Ozone is diamagnetic gas

    Solution 1:

    (a)     ONCl = 8 + 7 + 17 = 32 e

             ONO = 8 + 7 + 8 + 1 = 24 e (correct)

    (b)    JEE Ozone Question 2

    Central O-atom is sp2-hybridised with 1 lone pair, so bent shape (correct).

    (c) In solid state, ozone is violet-black. Ozone does not exist in solid state, thus incorrect.

    (d) O3 has no unpaired electrons, so diamagnetic (correct). Hence, (c) is the correct.

    Question 2:

    Which of the following statements about the depletion of ozone layer is correct?   [JEE Main 2014]             

    (a) The problem of depletion is less serious at poles because NO2 solidifies and is not available for consuming CIO° radicals

    (b) The problem of depletion is more serious at poles because ice crystals in the clouds over poles act as catalyst for photochemical reactions involving the decomposition of ozone by CI° and CIO° radicals.

    (c) Freons, chlorofluorocarbons, are inert chemically, they do not react with ozone in stratosphere

    (d) Oxides of nitrogen also do not react with ozone in stratosphere 

    Solution 2:

    Freons, chlorofluorocarbons, are inert chemically, they do not react with ozone in stratosphere.

    Hence, the correct option is (c).

    Question 3:

    Identify the wrong statements in the following:

    (a) Chlorofluorocarbons are responsible for ozone layer depletion

    (b) Greenhouse effect is responsible for global warming

    (c) Ozone layer does not permit infrared radiation from the sun to reach the earth

    (d) Acid rains is mostly because of oxides of nitrogen and sulphur

    Solution 3:

    Ozone layer does not allow ultraviolet radiation from sun to reach earth.

    Hence, the correct option is (c).

    Question 4:

    Ozone layer is made up of oxygen molecules and it is spread between 10 km to 50 km above the ground. We see mountaineers carrying oxygen cylinder and fighter pilots is bearing oxygen mask. Why they have to do so when there is already a layer of ozone above the ground?

    (a)  Because ozone is not useful for breathing

    (a)  Because layer of ozone is very high

    (c)  Because they do so for just precautions

    (d)  Because there is not sufficient ozone for breathing

    Solution 4:

    Ozone is not useful for breathing

    Hence, the correct option is (a).

    Question 5:

    Which of the following statements regarding ozone is not correct?

    (a) The oxygen-oxygen bond length in ozone is identical with that of molecular oxygen

    (b) The ozone is response hybrid of two structures

    (c) The ozone molecule is angular in shape

    (d) Ozone is used as a germicide and disinfectant for the purification of air.    

    Solution 5:        

    The oxygen–oxygen bond length in ozone is identical with that of molecular oxygen

    Hence, the correction option is (a).  

    Question 6:

    Consider the following statement about Ozone

    I. O3 is formed by the interaction of fluorine.

    II. It turns tetramethyl base paper as violet.

    III. It turns benzidine paper as brown.

    The correct set of true statement is

    (a) I and II

    (b) I, II and III

    (c) I and III

    (d) II and III    

    Solution 6:   

    Ozone is formed by the interaction of fluorine. It turns tetramethyl base paper and benzidine paper as violet and brown respectively.

    Hence, the correction option is (b).     

    Question 7:

    Assertion (A) It is necessary to use a silent electrical discharge in proportion of ozone to prevent its decomposition.

    Reason (R) Formation of ozone from oxygen is a exothermic process.

    (a) Both A and R are correct; R is the correct explanation of A

    (b) Both A and R are correct; R is not the correct explanation of A

    (c) A is correct; R is incorrect

    (c) R is correct; A is incorrect

    Solution 7:     

    It is necessary to use a silent electrical discharge in proportion of ozone to prevent its decomposition since the formation of ozone from oxygen is an endothermic process.

    Hence, the correction option is (c).

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