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Chemistry NEET Questions — Free MCQ Practice

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A cell $A g | A g^{+} | | C u^{+ +} |$ Cu initially contains $2 M A g^{+}$ and $2 M C u^{+ +}$ ions. The change in cell potential after the passage of 10 amp current for 4825 sec is :

A.

– 0.00738 V

B.

– 1.00738 V

C.

– 0.0038 V

D.

none

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Explanation

$(C) . Q = 10 \times 4825 = 48250 C$

no. of mole $= \frac{48250}{96500} = 0.5$

$A g + \frac{1}{2} C u^{+ +} \to A g^{+} + \frac{1}{2} C u 2.00 2.00 E_{c e l l} = E °_{c e l l} - \frac{0.0591}{1} \log \frac{[A g^{+}]}{{[C u^{+ +}]}^{1 / 2}} E_{1} = E °_{c e l l} - \frac{0.0591}{1} \log \frac{2.00}{{(2.00)}^{1 / 2}} E_{2} = E °_{c e l l} - \frac{0.0591}{1} \log \frac{2.00}{{(1.75)}^{1 / 2}} ∆ E = E_{2} - E_{1} = \frac{0.0591}{1} [\log \sqrt{2} - \log \frac{2.50}{\sqrt{1.75}}] = \frac{0.0591}{1} [\log 1.41 - \log 1.88] = \frac{0.0591}{1} [\log 1.492 - 0.2742] = - \frac{0.0591}{1} \times 0.125 = - 0.00738 V$

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Assertion : Fluorine cannot be prepared from fluorides by chemical oxidation.

Reason : Fluorine is the strongest oxidizing agent due to its highly positive standard potential.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

A). Fluorine is the strongest oxidizing agent due to its highly positive standard potential. Therefore, fluorine has the highest tendency to get reduced to $F^{-}$ , As a result, $F^{-}$ ion has the least tendency to get oxidised. That is why, fluorine cannot be prepared from fluorides by chemical oxidation.

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Assertion : : Sodium reacts with water at room temperature, whereas magnesium decomposes only hot water.

Reason : Sodium is more electropositive than magnesium.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

(A). Sodium reacts with water at room temperature, whereas magnesium decomposes only hot water because sodium is more electropositive than magnesium.

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Assertion : Silver nitrate solution becomes bluish when copper rod is placed in it.

Reason : Copper is more electropositive than silver.

A. If both the assertion and the reason are true and the reason is a correct explanation of the assertion B. If both the assertion and reason are true but the reason is not a correct explanation of the assertion C. If the assertion is true but the reason is false D. If both the assertion and reason are false

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Explanation

(A). Silver nitrate solution becomes bluish when copper rod is placed in it because copper $(E_{C u^{2 +} / C u}^{0} = 0.34 V)$ is more electropositive than silver $(E_{A g^{2 +} / A g}^{0} = 0.8 V)$ Therefore, copper is able to displace silver from silver nitrate solution. The dissolution of copper in the solution as $C u^{2 +}$ ions make it bluish.

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For a certain reaction a plot of [(c₀-c)/c] against time t, yields a straight line. c₀ and c are concentrations of reactant at t = 0 and t = t respectively. The rate of reaction is:

A.

3

B.

0

C.

1

D.

2

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Explanation

(d) For II order reaction (c₀-c)/c = K.t.c₀.

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Hydrogenation of vegetable ghee at 25⁰C reduces pressure of H₂ from 2 atom to 1.2 atom in 50 minute. The rate of reaction in terms of molarity per second is:

A.

1.09 x 10^-6

B.

1.09 x 10^-5

C.

1.09 x 10^-7

D.

1.09 x 10^-8

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Explanation

(b) The change in molarity=n/V = $∆$ P/RT = 0.8/(0.0821*298) = 0.0327

rate of reaction = change in molarity per sec = 0.0327/(50*60)=1.09*10^-5 mil litre^-1 sec^-1

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A hypothetical reaction, A₂ +B₂ $\to$ 2AB mechanism as given below;

A₂ $⇌$ A+ A ............(Fast)

A+B₂ → AB + B ............(Slow)

A+ B → AB ............(Fast)

The order of the overall reaction is:

A.

2

B.

1

C.

1.5

D.

zero

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Explanation

(c) r = k[A][B₂]

and K_c = [A][A]/[A₂] or [A] = k^1/2_c [A₂]^1/2

Thus, r = k . k^1/2_c [A₂]^1/2[B₂] = k'[A₂]^1/2[B₂]

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Following mechanism has been proposed for a reaction,

2A+B $\to$ D+E

A+B $\to$ C+D ...(Slow)

A+ C $\to$ E ...(Fast)

The rate law expression for the reaction is:

A.

r = K[A]²[B]

B.

r=K[A][B]

C.

r= K[A]²

D.

r= K[A][C]

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Explanation

(b) The rate expression is derived for slowest step of mechanism.

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In gaseous reactions important for the understanding of the upper atmosphere H₂O and O react bimolecularly to form two OH radicals. $∆$ H for this reaction is 72kJ at 500 K and E_a is 77 kJ mol^-1, then E_a for the bimolecular recombination of two OH radicals to form H₂O and O is:

A.

3 kJ mol^-1

B.

4 kJ mol^-1

C.

5 kJ mol^-1

D.

7 kJ mol^-1

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Explanation

(c) H₂O + O $\to$ 2OH; $∆$ H = 72KJ at 500K;

Given E_a = 77KJmol^-1

2OH $\to$ H₂O + O ; E_a.B.R

77=72+E_a.B.R

E_a.B.R = 5 KJmol^-1

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For a reaction A $\overset{}{\to}$ Product, rate law is $- \frac{d [A]}{d t} = K [A]_{0}$ . The concentration of A left after time t when $t = \frac{1}{K}$ is:

A.

$\frac{[A]_{0}}{e}$

B.

$[A]_{0} \times e$

C.

$\frac{[A]_{0}}{e^{2}}$

D.

$\frac{1}{[A]_{0}}$

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Explanation

(a) For I order reaction: $[A]_{t} = [A]_{0} \times e^{- K t} = [A]_{0} e^{- K \times \frac{1}{K}} = \frac{[A]_{0}}{e}$

Chemistry MCQs for NEET — Practice Questions with Answers

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