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WBJEE 2019 Chemistry Solved Paper

Question : 38 of 40

Marks: +1, -0

Identify the correct statement(s):

The oxidation number of Cr in $\mathrm{CrO}_5$ is +6.
ΔH > ΔU for the reaction $\mathrm{N}_2\mathrm{O}_4(g) \rightarrow 2\mathrm{NO}_2(g)$ . Provided both gases behave idelly.
pH of 0.1N $\mathrm{H}_2\mathrm{SO}_4$ is less than that of 0.1 N HCl at 25ºC
$\left(\frac{RT}{F}\right)$ = 0.0591 volt at 25ºC.

Solution:

(A,B)

(A) O.N. of grim

\mathrm{CrO}_5

= +6

(B)

\mathrm{N}_2\mathrm{O}_4(g) \rightarrow 2\mathrm{NO}_2(g)

ΔH = ΔU +

\Delta n_g RT

\Delta n_g

= 2 – 1 so ΔH > ΔU

(C) pH of 0.1 N

\mathrm{H}_2\mathrm{SO}_4

⇒

[H^{+}]

0.1 N

pH = –log

[H^{+}]

= 10 g

(10^{-1})

pH of 0.1 N HCl =

[H^{+}]

= 0.1 N

pH = log

[H^{+}]

= –log

(10^{-1})

= (1)

(D)

\frac{RT}{F} = \frac{8.314 \times 298}{96500}

= 0.256

\frac{2.303 RT}{F}

\frac{2.303 \times 8.314 \times 298}{96500}

= 0.0591

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