Chemistry Test - 11

Fluorocarbons such as freon-1 (CFCl₃) and freon-12 (CF₂Cl₂₎ emitted as propellants in aerosol spray cans, refrigerators, fire fighting reagents, etc. are stable compounds and chemically inert. They do not react with any substance with which they come in contact and thus float through the atmosphere unchanged and eventually enter the stratosphere. There they absorb UV radiations and break down liberating free atomic chlorine which causes decomposition of ozone. This results in the depletion of the ozone layer.

Acidity in ascending order =>  o-Nitrobenzoic acid >  p-Nitrobenzoic acid > m-Nitrobenzoic acid > Benzoic acid.

The acidity of ortho-nitrobenzoic acid is more as compared with para-nitrobenzoic acid because of the "ortho effect".

The explanation is relying on the steric inhibition of the resonance of the COOH group.

The ortho substituent forces the carboxyl group out of the plane of the benzene ring and decreases the resonance of the molecule.

At the same time carboxylate anion COO- have less sterically hindered and more apt to be in the energetically favorable planer configuration.

This makes an additional reason for the ortho-substituted acid to pass to the anion form thereby increasing its acidity as compared with the meta and para-substituted acids.

The correct match is(a)-(iv), (b)-(iii), (c)-(i), (d)-(ii).

(a) \(2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) \ldots\) Tropospheric pollution

(b) \(H O C l(g) \stackrel{h v}{\longrightarrow} H \dot{O}+\dot{C} l \ldots\) Ozone depletion

(c) \(\mathrm{CaCO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{CaSO}_{4}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \ldots\) Acid rain

(d) \(\mathrm{NO}_{2}(g) \stackrel{h v}{\longrightarrow} \mathrm{NO}(g)+\mathrm{O}(g) \ldots\) Photo chemical smog

Given,

\(\mathrm{K}=0.01 \mathrm{~s}^{-1} \)

\(\mathrm{t}_{\frac{1}{2}}=\frac{0.693}{0.01 }\)

\(\mathrm{t}_{\frac{1}{2}}=69.3 \mathrm{~s} \)

\({[R]=\frac{[R]_{0}}{2^{n}}} \)

\(2^{n}=\frac{[R]_{0}}{[R]} \)

\(2^{n}=\frac{2.4}{ 0.3} \)

\(2^{n}=8 \)

\(n=3 \text { (number of half-lives) } \)

For \(1\) half-life \(t_{\frac{1}{2}}=69.3 \mathrm{~s} \)

For \(3\) half-life \(3 t_{\frac{1}{2}}=3 \times 69.3 \mathrm{~s}\)

\(=207.9\mathrm{~s}^{-1}\)

Given,

Rate constant \((k)\)= \(4.606 \times 10^{-3} s ^{-1}\)

Equation for first order reaction:

\(t=\frac{2.303}{k} \log \frac{a}{a-x}\)

\(t=\frac{2.303}{(4.606 \times 10^{-3})} \log \frac{2}{0.2}\)

\(t=\frac{2.303}{(4.606 \times 10^{-3})}× 1\) \(\quad\quad\because (\log 10=1)\)

\(t=\frac{2.303}{(4.606 \times 10^{-3})}\)

\(t=500~s\)

Cfbelongs to the actinide series.

Actinides are the elements whose atomic number is from 90 to 103 .

The members of the series are Thorium, Protactinium, Uranium, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium. Ce is Cerium which is not an actinide. Ca is calcium and Cs is Cesium, both are not actinides.

Plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas as it has properties unlike those of the other states.

Convection is a mode of heat transfer by actual motion of matter.

Convection is the transfer of heat due to the bulk movement of molecules within fluids.Convection occurs on a large scale in atmospheres, oceans, planetary mantles.

The strength of oxyacids can also be decided with the help of the oxidation number of the central atoms.

The higher the oxidation number of the central atom, the more acidic is the oxyacid.

\(\begin{array}{cccc}+6 & +5 & +7 & +4 \\ \mathrm{H}_{2} \mathrm{SO}_{4} & \mathrm{HClO}_{3}{ } & \mathrm{HClO}_{4}{ } & \mathrm{H}_{2} \mathrm{SO}_{3}\end{array}\)

Order of acidic nature

\(\mathrm{HClO}_{4}>\mathrm{H}_{2} \mathrm{SO}_{4}>\mathrm{HClO}_{3}>\mathrm{H}_{2} \mathrm{SO}_{3}\)

Since, in \(\mathrm {H C l O_{4}}\), oxidation number of \(\mathrm {C l}\) is highest, so, \(\mathrm {H C l O_{4}}\) is the strongest acid among the given.

Phenol is acidic in nature because it liberates the acidic proton easily and the conjugate base is also resonance stabilized.

and

• When the Chloride group is introduced at the para position, it Has a -I effect towards the ring. Also, the +R effects operate at the ortho and para positions.
• We know that -I of Cl is dominating and hence it helps in increasing the overall acidity of phenol.
• But, the -R effect of the nitro group dominates the -I of chlorine making nitro phenols more acidic than chlorophenols.

Comparison between

In the case of ortho nitrophenol, the negative charge is delocalized by -R of the nitro group.

But -R does not operate in the case of meta nitrophenol and thus it is less acidic than ortho nitrophenol.

Comparison between:

• There exists an intramolecular H bonding in ortho nitrophenol which makes the release of proton much more difficult.

Thus, the most acidic compound is .