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1

NEET 2016 Phase 2

MCQ (Single Correct Answer)
If the Eocell for a given reaction has a negative value, which of the following gives the correct relationships for the values of $$\Delta $$Go and Keq ?
A
$$\Delta $$Go > 0;   Keq < 1
B
$$\Delta $$Go > 0;   Keq > 1
C
$$\Delta $$Go < 0;   Keq > 1
D
$$\Delta $$Go < 0;   Keq < 1

Explanation

We know that

$$\Delta $$Go = –nFEocell

Eocell = -ve then $$\Delta $$Go = +ve or $$\Delta $$Go > 0

$$\Delta $$Go = -nRTlog Keq

For $$\Delta $$Go = +ve, Keq = -ve or Keq < 1.
2

NEET 2016 Phase 2

MCQ (Single Correct Answer)
During the electrolysis of molten sodium chloride, the time required to produce 0.10 mol of chlorine gas using a current of 3 amperes is
A
55 minutes
B
110 minutes
C
220 minutes
D
330 minutes

Explanation

At cathode : 2Na+ + 2e $$ \to $$ 2Na

At anode : 2Cl $$ \to $$ Cl2 + 2e
----------------------------------------------

Net reaction: 2Na+ + 2Cl $$ \to $$ 2Na + Cl2

From Faraday’s first law of electrolysis,

w = Z$$ \times $$I$$ \times $$t

= $${E \over {96500}}$$$$ \times $$I$$ \times $$t

No. of moles of Cl2 gas × Mol. wt. of Cl2 gas

= $${{Eq.\,wt.\,of\,C{l_2}\,gas \times I \times t} \over {96500}}$$

$$ \Rightarrow $$ 0.10 $$ \times $$ 71 = $${{35.5 \times 3 \times t} \over {96500}}$$

$$ \Rightarrow $$ t = $${{0.10 \times 71 \times 96500} \over {35.5 \times 3}}$$

= 6433.33 sec

= 107.22 min $$ \simeq $$ 110 min
3

NEET 2016 Phase 2

MCQ (Single Correct Answer)
The number of electrons delivered at the cathode during electrolysis by a current of 1 ampere in 60 seconds is (charge on electron = 1.60 $$ \times $$ 10$$-$$19C)
A
6 $$ \times $$ 1023
B
6 $$ \times $$ 1020
C
3.75 $$ \times $$ 1020
D
7.48 $$ \times $$ 1023

Explanation

Q = I × t

Q = 1 × 60 = 60 C

Now, 1.60 × 10–19 C $$ \equiv $$ 1 electron

$$ \therefore $$ 60 C $$ \equiv $$ $${{60} \over {1.6 \times {{10}^{ - 19}}}}$$

= 3.75 $$ \times $$ 1020 electrons
4

NEET 2016 Phase 2

MCQ (Single Correct Answer)
Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because
A
zinc is lighter than iron
B
zinc has lower melting point than iron
C
zinc has lower negative electrode potential than iron
D
zinc has higher negative electrode potential than iron

Explanation

The reduction potential values are

Zn2+/Zn = – 0.76 V

Fe2+/Fe = – 0.44 V

Thus, due to higher negative electro potential value of zinc than iron, iron cannot be coated on zinc.

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