TS EAMCET 2019 :: Chemistry :: General questions

• Chemistry - General questions

 Benzaldehyde can be converted to benzonitrile by treatment with

Answer:

Explanation:

 When benzaldehyde reacts with $NH_{2}OH$ (hydoxyl amine)  then oxime is formed . Further oxime gives benzonitrile  on heating 

 Thus, option (c) is correct

Match the following

Answer:

Explanation:

(A-II)  Neoprene is prepared from chloroprene. 

Neoprene is synthetic rubber or elastomer and used in laptop sleeves, orthopaedic braces, electrical insulation and automotive fan belts.

(B-III)   Monomer unit of nylon-6  , 6 are adipic acid and hexamethylenediamine.

Nylon-6,6 is fiber and used in airbags, apparel, carpet fibers, oil pans, ball bearing cages, radiation tan etc.

(C-IV)  High-density polyethene (HDP) is prepared in presence of the Ziegler-Natta catalyst.It is harder and opaque  and can withstand somewhat higher temperature for short time periods

(D-I)

Melamine formaldehyde resin used in kitchen utensils and plates.It is also used in formation of decorative paper.

Melamine-formaldehyde resin tightly packed by cross-linked network.

Statement (A) Mg can reduce $Al_{2}O_{3}$ above  $1350^{0} C$

 Statement (B)   Al can reduce MgO below $1350^{0} C$

 The correct answer is 

Answer:

Explanation:

Mg can reduce $Al_{2}O_{3}$ below 1350° C according to the Ellingham diagram. On the other hand, Al can reduce MgO above $1350^{0} C$. Thus, both statements (A) and (B)  are incorrect.

A solution of 17.1 w% of surcose (molar mass =$342g mol^{-1}$)  is isotonic with a x w% solution of oxalic acid (molar mass =90g mol^-1)  . assume the degree of dissociation of  oxalic acid as 0.01 . what is x?

Answer:

Explanation:

Given,

 mass of sucrose (w₁) =1.71 g

 Molar mass of sucrose (M1)=342 g mol^-1

 Mass of oxalic  acid (w₂) =xg

 Molar mass of oxalic acid (M₂)  = 90 g mol^-1

 Degree of dissociation ($\alpha$)  of oxalic acid =0.01

  Step I To find the value of van't Hoff factor (i) 

$i= (1- \alpha)+n \alpha$

 where, n= number of parts in which one molecule of oxalic acid dissociates (=3)

 i=(1-0.01)+(3 x 0.01)

i= 0.99+0.03

   i=1.02

Step II  To find the value of (x)

 For isotonic  solutions:

 $\pi$ (sucrose) = $\pi $ ( oxalic acid)     [ $\because \pi =CRT$]

 or, Molarity (sucrose)  = i Molarity (oxalic acid)

 $\frac{w_{1}}{M_{1}} (sucrose) = i \times  ( \frac{x}{ M_{2}})$ (oxalic acid )

 $x= \frac{w_{1}}{M_{1}}\times\frac{M_{2}}{i}=\frac{17.1\times90}{1.02\times342}$

 $x= \frac{1539}{348.84}=4.41 g$

 hence, value of x=4.41 g

 Hence, option (c)  is correct.

Calculate the depression in the freezing point of a solution  containing 0.1 g of $K_{3}[Fe(CN)_{6}]$ in 100 g of $H_{2}O$? (molecular  weight of  $K_{3}[Fe(CN)_{6}]$ =369; $K_{f}$=1.86 K Kg mol^-1)

Answer:

Explanation:

Given,

Mass of  $K_{3}[Fe(CN)_{6}]$ =0.1 g

 Mass of solvent =100 g

 Molar mass of $K_{3}[Fe(CN)_{6}]$ =329 g mol^-1 

$k_{f}$ =1.86 K kg/mol

$K_{3}[Fe(CN)_{6}]\rightleftharpoons3K^{+}+Fe(CN)_{6}]^{-}$

 i(van't Hoff factor)=3+1=4

 From, depression in freezing point,

$T_{f} =i \times K_{f} \times m $

 $T_{f}= 4 \times 1.86 K kg  /mol \times \frac{0.1 g}{329 g} \times  \frac{1000}{100 kg}$

 $T_{f}=0.0226 K$

Thus, option (c)  is correct

• Chemistry - General questions