In modern periodic table while going from top to b | Chemistry Questions & Answers

Q:

The reduction potential of hydrogen half-cell will be negative if :
(1) $P (H_{2})$ = 2 atm and [H+] = 2.0 M
(2) $P (H_{2})$ = 1 atm and [H+] = 2.0 M
(3) $P (H_{2})$ = 1 atm and [H+] = 1.0 M
(4) $P (H_{2})$ = 2 atm and [H+] = 1.0 M

A) Option 1	B) Option 2
C) Option 3	D) Option 4

Answer & Explanation Answer: D) Option 4

Explanation:

$H^{+} - e^{-} \to \frac{1}{2} H_{2}$

Apply Nernst equation

$E = 0 - \frac{0.059}{1} \log (\frac{P H_{2}^{\frac{1}{2}}}{[H^{+}]})$

$E = - \frac{0.059}{1} \log (\frac{2^{\frac{1}{2}}}{1})$

Therefore E is Negative

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26 15299

Q:

Trichloroacetaldehyde was subject to Cannizzaro's reaction by using NaOH. The mixture of the products contains sodium trichloroacetate and another compound. The other compound is :

A) Chloroform	B) 2, 2, 2-Trichloroethanol
C) Trichloromethanol	D) 2, 2, 2-Trichloropropanol

Answer & Explanation Answer: B) 2, 2, 2-Trichloroethanol

Explanation:

$\begin{matrix} C l \\ | \\ C l & - & C & - & C H O \\ | \\ C l \end{matrix}$ $\to_{C a n n i z z a r o' s R e a c t i o n}^{N a O H}$ $\begin{matrix} C l \\ | \\ C l & - & C & - & C O O N a \\ | \\ C l \end{matrix}$ $+$ $\begin{matrix} C l \\ | \\ C l & - & C & - & C H_{2} \\ | 2 & 1 \\ C l \end{matrix}$ $- O H$

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7 5221

Q:

Silver Mirror test is given by which one of the following compounds?

1. Benzophenone

2. Acetaldehyde

3. Acetone

4. Formaldehyde

A) Only 1	B) Only 2
C) 1 and 3	D) 2 and 4

Answer & Explanation Answer: D) 2 and 4

Explanation:

Both Formaldehyde and Acetaldehyde will give this test

$H C H O \overset{[A g (N H_{3})_{2}^{+}]}{\to} \overset{A g}{S i l v e r m i r r o r} + O r g a n i c c o m p o u n d$

$C H_{3} - C H O \overset{[A g (N H_{3})_{2}^{+}]}{\to} \underset{S i l v e r m i r r o r}{A g} + O r g a n i c c o m p o u n d$

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66 65767

Q:

The entropy change involved in the isothermal reversible expansion of 2 moles of an ideal gas from a volume of 10 $d m^{3}$ at 27°C is to a volume of 100 $d m^{3}$

A) 42.3 J/ mole / K	B) 38.3 J/ mole / K
C) 35.8 J/ mole / K	D) 32.3 J/ mole / K

Answer & Explanation Answer: B) 38.3 J/ mole / K

Explanation:

$∆ s = n R \ln \frac{v 2}{v 1}$

$= 2.303 n R \log \frac{v 2}{v 1}$ = $2.303 \times 2 \times 8.314 \times \log (\frac{100}{10})$ = $38.3 J$ $m o l^{- 1}$ $k^{- 1}$

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43 16197

Q:

A gas absorbs a photon of 355 nm and emits at two wavelengths. If one of the emissions is at 680 nm, the other is at :

A) 518 nm	B) 1035 nm
C) 325 nm	D) 743 nm

Answer & Explanation Answer: D) 743 nm

Explanation:

$\frac{1}{λ} = \frac{1}{λ 1} + \frac{1}{λ 2}$

$\frac{1}{355} = \frac{1}{680} + \frac{1}{λ 2}$

$\frac{1}{λ 2} = \frac{680 - 355}{680 \times 355}$

$\Rightarrow λ 2 = 743 n m$ .

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12 9309

Q:

In a face centred cubic lattice, atom A occupies the corner positions and atom B occupies the face centre positions. If one atom of B is missing from one of the face centred points, the formula of the compound is

1) $A_{2} B_{5}$

2) $A_{3} B_{2}$

3) $A_{2} B_{3}$

4) $A_{3} B_{4}$

A) Option 1	B) Option 2
C) Option 3	D) Option 4

Answer & Explanation Answer: A) Option 1

Explanation:

$Z_{A} = \frac{8}{8}$ ; $Z_{B} = \frac{5}{2}$

So formula of compound is $A B_{\frac{5}{2}}$

i.e., $A_{2} B_{5}$ .

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13 9148

Q:

The degree of dissociation ( $α$ ) of a weak electrolyte, $A_{x} B_{y}$ is related to van't Hoff factor (i) by the expression:

$1 . α = \frac{x + y + 1}{i - 1}$

$2 . α = \frac{x + y - 1}{i - 1}$

$3 . α = \frac{i - 1}{x + y + 1}$

$4 . α = \frac{i - 1}{x + y - 1}$

A) 1 is correct	B) 2 is correct
C) 3 is correct	D) 4 is correct

Answer & Explanation Answer: D) 4 is correct

Explanation:

Van't Hoff factor (i) = $\frac{O b s e r v e d C o l l i g a t i v e P r o p e r t y}{N o r m a l C o l l i g a t i v e P r o p e r t y}$

$\begin{matrix} A_{x} B_{y} \\ 1 - α \end{matrix} \to \begin{matrix} x A^{+ y} \\ x α \end{matrix} + \begin{matrix} y B^{- x} \\ y α \end{matrix}$

Total Moles = $1 - α + x α + y α$ = $1 - α (x + y - 1)$

$i = \frac{1 + α (x + y - 1)}{1}$

$\Rightarrow α = \frac{i - 1}{x + y - 1}$

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6 7270

Q:

Ozonolysis of an organic compound gives formaldehyde as one of the products. This confirms the presence of :

A) An acetylenic triple bond	B) Two ethylenic double bonds
C) A vinyl group	D) An isopropyl group

Answer & Explanation Answer: C) A vinyl group

Explanation:

$C =} C H_{2} \overset{O z o n o l y s i s}{\to} H C H O$

Vinylic group.

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3 4824

A) size of an atom increases	B) size of an atom decreases
C) ionisation energy of an atom increases	D) size and ionisation energy of an atom increases

In modern periodic table while going from top to bottom in a group ______.

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