JEE 2011 :: General Questions :: Chemistry

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According to kinetic theory of gases

Answer:

Explanation:

(a) According to a postulate of the kinetic theory of gases, a collision between the molecules as well as with the wall of a container is perfectly elastic in nature.

(b) lf a gas molecule of man 'm' moving with speed 'u' collide to the wall of the container, the change in momentum is $\triangle$p= -2mu.Therefore heavier molecules will transfer more momentum to the wall as there will be greater change in the momentum of the colliding gas molecule. However, this was not postulated in the kinetic theory of Gases.
(c) According to Maxwell-Boltzmann's distribution of molecular speed, very few molecules have either very t ist or very low speeds. Most of the molecules move in a specific
intermediate speed range.
(d) According to the kinetic theory of gases, a gas molecule moves in a straight line unless it collides with another molecular or to  the wall of the container and a change in momentum is observed only after collision

The correct statement(s) pertaining to the adsorption of a gas on a solid surface is(are)

Answer:

Explanation:

(a) In the process of adsorption, a bond is formed between adsorbate and adsorbent. Hence always exothermic.
(b) Physisorption requires very low activation energy while chemisorption requires high activation energy. Therefore physisorption may transform into chemisorption but only at high temperatures.
(c) It is a wrong statement as at higher temperature, physically adsorbed substance starts desorbing.
(d) In physical adsorption, van der Waals' force hold the adsorbate and adsorbent together which is a weak electrostatic attraction. In chemisorption, a strong chemical bond binds the
adsorbate to the adsorbent. Therefore, chemisorption is more exothermic than physical adsorption

Among the foliowing compounds, the most acidic is

Answer:

Explanation:

A monosubstituted benzoic acid is stronger than a monosubstituted phenol as the former is a carboxylic acid. Among the given substituted benzoic acid, ortho-hydroxy acid is the strongest acid although -OH causes electron donation by resonance effect which tends to decrease acid strength. It is due to a very high stabilization of conjugate base by intramolecular H-bond which outweight the electron-donating resonance effect of  _OH.

The overall order of acid-strength of given four acids is ortho-hydro xy benzoic acid

$(pK_{a}=2.98)>$ Toluic acid  $pK_{a}=4.37) >$ p-hydroxybenzoic acid  $(pK_{a}=4.58)>$

p-nitrophenol  $(pK_{a}=7.15)$

Dissolving 120 g of urea (molecular weight 60) in 1000 g of water gave a solution of density 1.15 g /mL. The molarity of the solution is

Answer:

Explanation:

 Molarity = Moles  of solute/Volume of solution(L)

Moles of urea= $\frac{120}{60}=2$

weight of solution =weight  of solvent+weight of solute=1000+120=1120g

$\Rightarrow$  Volume =$\frac{1120g}{1.15 g/mL} \times \frac{1}{1000mL/L}=0.974 L \Rightarrow  Molarity=\frac{2000}{0.974}=2.05M$

Extra pure $N_{2}$ can be obtained by heating

Answer:

Explanation:

 $Ba(N_{3})_{2} \underrightarrow{heat} Ba(s)+3N_{2}(g)$

Azide salt of barium can be obtained in purest form as well as the decomposition product contain solid Ba as byproduct along with gaseous nitrogen, hence no additional step of separation is required. Other reactions are

  $NH_{4}NO_{3} \underrightarrow{heat} N_{2}O+2H_{2}O$

$2NH_{3}+3CuO \underrightarrow{heat} 3Cu+3H_{2}O+N_{2}$

  $ (NH_{4})_{2}Cr_{2}O_{7} \underrightarrow{heat}  Cr_{2}O_{3}+4H_{2}O+N_{2}$

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