JEE 2018 :: Chemistry (2018) :: Solved questions (2018)

• Chemistry (2018) - Solved questions (2018)

Total  number of lone pair of electron in $I_{3}^{-}$ ion is

Answer:

Explanation:

The structure of $I_{3}^{-}$ is

Hence, 9 is the correct answser

Which of the following are Lewis acids?

Answer:

Explanation:

Key Idea Lewis acids are defined as, "Electron deficient compounds which have the ability to accept at least one lone pair,"

The compound given are

PH₃- Octet complete although P has vacant 3d-orbital but does not have the tendency to accept lone pair in it. Hence, it cannot be considered as Lewis acid.

BCl₃- In complete octet with following orbital picture.

Hence, vacant p-orbital of B can accept one lone pair thus it can be considered as Lewis acid.

AlCl₃ - Similar condition is visible in AlCl₃ as well i.e.

Al( Valance orbital only)=

Hence this compound can also be considered as Lewis acid.

SiCl₄  - Although this compound does not have incomplete octet but it shows the tendency to accept lone pair of electrons in its vacant d- orbital. This tendency of SiCl₄ is visible in the following reaction.

Thus option (b) and (c) both appear as correct but most suitable answers is (c) as a condition of a proper Lewis acid is more well defined in BCl3  and  AlCl₃.

Which of the following lines correctly show the temperature dependance of equilibrium constant  K, for an exothermic reaction?

Answer:

Explanation:

From thermodynamics,

$ln k=\frac{-\triangle H^{o}}{RT}+\frac{\triangle S^{o}}{R}$     ......(i)

Mathematically, the equation of straight line is

  $y-c+mx$    .....(ii)

After comparing Eq. (ii) with (i) we get,

slope= $\frac{\triangle H^{o}}{R}$ and intercept= $\frac{\triangle S^{o}}{R}$

Now, we know for exothermic reaction $\triangle H$ is negative(-)ve. But here,

Slope = $\frac{\triangle H^{o}}{R}$ is postive

So, lines A and B in the graph represent temperature dependence of equilibrium constant K for an exothermic reaction as shown below

Which type of 'defect' has the presence of cations in the interstitial sites?

Answer:

Explanation:

It is the "Frenkel defect" in which cations leave their original site and occupy interstitial site as shown below.

According to molecular orbital theory, which of the following will not be a viable molecule?

Answer:

Explanation:

Key Idea According to M.O.T . the viability of any molecule can be judged through the calculation of bond order.

The molecule having ero bond order will not be viable hence, $H_{2}^{2-}$(option c) is the correct answer

• Chemistry (2018) - Solved questions (2018)