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 From the following statements regarding $H_{2}O_{2}$, choosing the incorrect statement.

Answer:

Explanation:

  $H_{2}O_{2}$ act as an oxidising as well as reducing agent, because, oxidation number of oxygen in  $H_{2}O_{2}$ is -1. So, it can be oxidised to oxidation state 0 or reduced to oxidation state -2

  $H_{2}O_{2}$ decomposes on exposure to light. So, it has to be stored in plastic or wax-lined glass bottles in dark for the prevention of exposure. It also has to be kept away from the dust

In the context of the Hall-Heroult process for the extraction of Al, which of the following  statements is false?

Answer:

Explanation:

(a) In the Hall-Heroult process. for extraction of Al, carbon anode is oxidised to CO and CO₂

(b) When Al₂ O₃ is mixed with CaF₂. It lowers the melting  point of the mixture  and brings conductivity

(c) Al³⁺   is reduced at the cathode to form Al.

(d) Here, Al₂O₃   is an electrolyte, undergoing the redox process, Na₃ AlF₆   although is an electrolyte but serves as a solvent. not electrolyte.

 The ionic radii (in Å ) of N^3-,O^2- and F^- respectively are

Answer:

Explanation:

Number of elecrons in N^3-   =7+3=10

 Number of electrons O^2-= 8+2=10

Number of electrond F^-  = 9+1=10

 Since all three species have every 10 electrons  hence they are isoelectronic species

  It is considered  that, in case  of isoelectronic species as the negative charge increases, ionic radii increases and therefore the value  of ionic radii are 

 N^3-  =1.71  (highest among the three0

 O^2-   =1.40

  F ^- = 1.36  9 lowest among the three)

Time Saving Technique.  There is no need to mug up the radius values for different  ions,  The particular question  can be solved  through following time saving.

Trick. The charges  on the ions indicate the size as  N³⁺   > O^2-    > F ^-  . Thus , you have to look for the option in which the above trend is followed. Option (c) is only one in which this trend is followed. Hence, it is the correct answer.

3 g of activated charcoal was added to 50 mL of acetic acid solution (0.06 N) in a flask. After an hour it was filtered and the strength of the filtrate was found to be 0.042 N. The amount of acetic acid adsorbed (per  gram of charcoal ) is

Answer:

Explanation:

Given, initial strength od acetic acid =0.06 N

 Final strength =0.042 N

Volume given  =50mL

 $\therefore$  Initial m moles of   $CH_{3}COOH$

 $=0.06\times50=3$

 Final m moles of  $CH_{3}COOH$

 $=0.042\times50=2.1$

 $\therefore$     m moles of $CH_{3}COOH$ adsorbed =3-2.1  =0.9m mol

 Hence , mass of $CH_{3}COOH$ absorbed per gram of charcoal

                                         $=\frac{0.9\times60}{3}$

  (   $\therefore$ molar mass of  $CH_{3}COOH$  = 60gmol^-1 )

                           $=\frac{54}{3}=18 mg$

 Higher order ( >3) reactions are rare due to

Answer:

Explanation:

 The main conditions for the occurrence of a reaction is proper orientation and effective collision of the reactants.

  Since the chances of simultaneous collision with proper orientation between more than 3 species is very rare, so reaction with order greater than 3 is rare.

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• Main 2015 - Chemistry 2015
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