JEE 2013 :: Advanced 2013 :: Chemistry 2013

• Advanced 2013 - Physics 2013
• Advanced 2013 - Chemistry 2013
• Advanced 2013 - Mathematics 2013

Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at 25° C . For this process, the correct statement is 

Answer:

Explanation:

Plan  Physical  adsorption takes place with a decrease in enthalpy thus exothermic change

It is physical adsorption and does not require activation. Thus, (a) is incorrect.

Being  physical adsorption  $\triangle$ H <0  thus, (b) is correct. An exothermic reaction is favoured at low temperature thus (c) is incorrect.

 Physical adsorption is always reversible, thus (d) is incorrect.

Upon treatment with ammonical H₂S , the metal ion that precipitates as a sulphide is

Answer:

Explanation:

 Plan   K_sp(ZnS)   is very high and Zn²⁺  is precipitated as ZnS by high concentration of S^2-   formed when H₂S is  passed in ammoniacal  solution

   $H_{2}S\rightleftharpoons Zn^{+}+S^{2-}   $(I)

$H^{+}+OH^{-}\rightleftharpoons H_{2}O $(II)

Reaction (I) is favoured  in forward side if H⁺  is  removed immediately by OH^-  (NH₄OH)

$Zn^{2+}+S^{2-}\rightarrow ZnS\downarrow$

                                             white ppt.

 Fe³⁺  and Al³⁺  are precipitated as hydroxide

The arrangement of X^- ions around A⁺ ion in solid AX is  given in the figure (not drawn to scale ) . If tythe radius of X^- is 250 pm, the radius of A^- is 

Answer:

Explanation:

Plan  Given arrangement represents octahedral  void and fix this 

                   $\frac{r_{+}(cation)}{r_{-}(anion)}=0.414$

$\frac{r(A^{+})}{r(X^{-})}=0.414$

 $r(A^{+}){}=0.414\times r(X^{-})$

   $=0.414\times250pm=103.5 pm$

 Concentrated nitric acid , upon long standing turns yellow-brown due to the formation of 

Answer:

Explanation:

Plan NO₂ is a brown coloured gas and imparts  this colour to  concentrated HNO₃  due to long-standing  

$4HNO_{3}\rightarrow 2H_{2}0+2NO_{2}+3O_{2}$

In the reaction, P+Q →  R+S

 the time taken for 75% reaction of P twice the time taken for 50% reaction of P . The concentration of Q varies with reaction time as shown in the figure. The overall order of the reaction is 

Answer:

Explanation:

Plan    Time of 75%  reaction is twice the time taken for 50%  reaction if it is first order reaction w.r.t P . From graph ,[Q} decrease lineraly with time ,  thus  it is  zeroth order reaction  w.r.t Q

$\frac{dx}{dt}=K[P]^{a}[Q]^{b}$

  Order w.r.t   P=a=1

Order w.r.t   Q= b=0

  Thus overall prder  of the reaction

                 =1+0=1

• Advanced 2013 - Physics 2013
• Advanced 2013 - Chemistry 2013
• Advanced 2013 - Mathematics 2013