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1

### JEE Main 2021 (Online) 27th August Morning Shift

Numerical
The reaction that occurs in a breath analyser, a device used to determine the alcohol level in a person's blood stream is

$$2{K_2}C{r_2}{O_7} + 8{H_2}S{O_4} + 3{C_2}{H_6}O \to 2C{r_2}{(S{O_4})_3} + 3{C_2}{H_4}{O_2} + 2{K_2}S{O_4} + 11{H_2}O$$

If the rate of appearance of Cr2(SO4)3 is 2.67 mol min$$-$$1 at a particular time, the rate of disappearance of C2H6O at the same time is _____________ mol min$$-$$1. (Nearest integer)

## Explanation

$$\left( {{{Rate\,of\,disappearance\,of\,{C_2}{H_6}O} \over 3}} \right)$$

$$= \left( {{{Rate\,of\,disappearance\,of\,C{r_2}{{(S{O_4})}_3}} \over 2}} \right)$$

$$\Rightarrow \left( {{{2.67\,mol/\min \, \times 3} \over 2}} \right) =$$ rate of disappearance of C2H6O.

$$\Rightarrow$$ Rate of disappearance of C2H6O = 4.005 mol/min.
2

### JEE Main 2021 (Online) 26th August Evening Shift

Numerical
The reaction rate for the reaction

[PtCl4]2$$-$$ + H2O $$\rightleftharpoons$$ [Pt(H2O)Cl3]$$-$$ + Cl$$-$$

was measured as a function of concentrations of different species. It was observed that $${{ - d\left[ {{{\left[ {PtC{l_4}} \right]}^{2 - }}} \right]} \over {dt}} = 4.8 \times {10^{ - 5}}\left[ {{{\left[ {PtC{l_4}} \right]}^{2 - }}} \right] - 2.4 \times {10^{ - 3}}\left[ {{{\left[ {Pt({H_2}O)C{l_3}} \right]}^ - }} \right]\left[ {C{l^ - }} \right]$$.

where square brackets are used to denote molar concentrations. The equilibrium constant Kc = ____________ . (Nearest integer)

## Explanation

[PtCl4]2$$-$$ + H2O $$\rightleftharpoons$$ [Pt(H2O)Cl3]$$-$$ + Cl$$-$$

$${{ - d{{\left[ {PtC{l_4}} \right]}^{ - 2}}} \over {dt}} = 4.8 \times {10^{ - 5}}\left[ {PtC{l_4}^{ - 2}} \right] - 2.4 \times {10^{ - 3}}[Pt({H_2}O)C{l_3}][\mathop u\limits^o ]$$

$$\Rightarrow {K_{eq}} = {{{k_f}} \over {{k_b}}} = {{4.8 \times {{10}^{ - 5}}} \over {2.4 \times {{10}^{ - 3}}}} = 0.02$$
3

### JEE Main 2021 (Online) 26th August Evening Shift

Numerical
The overall stability constant of the complex ion [Cu(NH3)4]2+ is 2.1 $$\times$$ 1013. The overall dissociations constant is y $$\times$$ 10$$-$$14. Then y is __________. (Nearest integer)

## Explanation Given ks = 2.1 $$\times$$ 1013

Kd = $${1 \over {{k_s}}}$$ = 4.7 $$\times$$ 10$$-$$14

$$\therefore$$ y = 4.7 $$\approx$$ 5
4

### JEE Main 2021 (Online) 26th August Morning Shift

Numerical
The following data was obtained for chemical reaction given below at 975 K.

2NO(g) + 2H2(g) $$\to$$ N2(g) + 2H2O(g) The order of the reaction with respect to NO is ___________. [Integer answer]

## Explanation

7 $$\times$$ 10$$-$$9 = K $$\times$$ (8 $$\times$$ 10$$-$$5)x (8 $$\times$$ 10$$-$$5)y ......... (1)

2.1 $$\times$$ 10$$-$$8 = K $$\times$$ (24 $$\times$$ 10$$-$$5)x (8 $$\times$$ 10$$-$$5)y ....... (2)

$${1 \over 3} = {\left( {{1 \over 3}} \right)^x} \Rightarrow x = 1$$

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