Q21 of 37 Page 1

Calculate the number of lone pairs on central atom in the following molecule and predict the geometry.

XeF4




Structure of XeF4


So, the number of lone pairs is 2.


According to the VSEPR theory, any AX4E2 species with 2 lone pairs (E) is square planar where A is the central atom and X are the similar bonded atoms. So, XeF4 is square planar.


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19

Assertion: C2H5OH is a weaker base than phenol but is a stronger nucleophile than phenol. (1)

Reason: In phenol the lone pair of electrons on oxygen is withdrawn towards the ring due to resonance.


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Assertion: Aryl halides undergo nucleophilic substitution reactions with ease.

Reason: The carbon halogen bond in aryl halides has partial double bonds character.


 22

The rate of a reaction depends upon the temperature and is quantitatively expressed as

k = A e


i) If a graph is plotted between log k and 1/T, write the expression for the slope of the reaction?


ii) If at under different conditions Ea1 and Ea2 are the activation energy of two reactions. If Ea1 = 40 J / mol and Ea2 = 80 J / mol. Which of the two has a larger value of the rate constant?


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The experimentally determined molar mass for what type of substances is always lower than the true value when water is used as solvent. Explain. Give one example of such a substance and one example of a substance which does not show a large variation from the true value.