MHT CET 2020 :: Chemistry :: General questions

• Chemistry - General questions

 Identify compound 'B' in following series of reactions?

 Acetonitrile    $\underrightarrow{Na/alcohol}$  A  $\underrightarrow{NaNo_{2}/dil.HCl}$   B

Answer:

Explanation:

 In the given reaction , acetonitrile (CH₃CN) on reaction with Na/alcohol  ethyl amine [A] (CH₃ CH₂ NH₂ ) . Which on further reaction with NaNO₂ /dil. HCl  followed by hydrolysis gives ethyl alcohol [B]

$CH_{3}CN$   $\underrightarrow{Na/alcohol}$ $CH_{3}CH_{2}NH_{2}$

 Acetonitrile                               Ethyl amine [A]

$\underrightarrow{NaNO_{2}/dil.HCl}$            $CH_{3}CH_{2}OH$

                                Ethyl Alcohol

                                       [B]

 Which of the following actinoids exhibits only +3 oxidation state?

Answer:

Explanation:

 Lawrencium (Lr) shows only 3+ oxidation state, that has  electronic  configuration [Rn]  5f¹⁴ 7s² 7p¹ . This element may easily give up three valance electron from the 7s and 7p subshell to form a stable +3 oxidation state. the state is especially stable in case of Lr  because it contains full-filled (5 f¹⁴ ) f-subshell.

 Which of the following reaction  of diazonium salt involves retention of diazonium group?

Answer:

Explanation:

 Reaction with phenol of diazonium salt involves retention of the diazonium group.

 Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para-position is coupled with the diazonium salt to form p-hydroxyazobenzene. This type of reaction known as coupling reaction

 Which of the following is obtained by catalytic oxidation of ammonia?

Answer:

Explanation:

 Nitric oxide (NO)  is obtained by catalytic oxidation of ammonia. The catalytic oxidation of ammonia uses a metal catalyst such as platinum, copper or nickel. This metal catalyst is heated, so that ammonia can reduce it, oxygen added to the system can then oxidise the ammonia, forming nitric oxide.

$4NH_{3}+5O_{2} $  $\underrightarrow{Pt gauge}$    $4NO+6H_{2}O;+21.5kcal$

                        800-900° C

An ideal gas expands isothermally  and reversibly from 10m³ to 20m³ at 300 K, performing 5.187 kj of work on surrounding, calculate the number of moles of gas used

Answer:

Explanation:

$W=-\int p_{ext}.dV$

 Since the process is reversible, p_ext=p, which gives

$W=-\int p.dV$

 Substituting the ideal gas equation for p leads to

$W=-\int \frac{nRT}{V}.dV$

 since the process is isothermal,

$W=-nRTln\left(\frac{V_{2}}{V_{1}}\right)$

 $-5.187\times1000 J=-n\times8.314JK^{-1}mol^{-1}$

                                                          $ln\left(\frac{20m^{3}}{10m^{3}}\right)$

$\Rightarrow  n=\frac{5.187\times1000}{8.314\times ln2}mol$

$ =\frac{5.187\times1000}{8.314\times 0.6931}mol=3 mol$

• Chemistry - General questions