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Standard XII

Chemistry

First Order Reaction

Zn+2H+→ Zn2++...

Question

$Z n + 2 H^{+} \to Z n^{2 +} + H_{2}$
Half-life period is independent of the concentration of zinc at constant pH. For the constant concentration of Zn, the rate becomes 100 times when pH is decreased from 3 to 2. Hence:

\frac{d x}{d t} = k [Z n]^{0} [H^{+}]^{2}

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(\frac{d x}{d t}) = k [Z n] [H^{+}]^{2}

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Rate is not affected if concentration of zinc is made four times and that of

H^{+}

ion is halved.

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Rate becomes four times if concentration of

H^{+}

ion is doubled at constant Zn concentration.

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Solution

The correct options are
B $(\frac{d x}{d t}) = k [Z n] [H^{+}]^{2}$
C Rate is not affected if concentration of zinc is made four times and that of $H^{+}$ ion is halved.
D Rate becomes four times if concentration of $H^{+}$ ion is doubled at constant Zn concentration.
For first order reaction, half-life is independent of initial concentration.
$\frac{d x}{d t} = k [H^{+}]^{a} [Z n] = k^{'} [Z n]$
$k^{'} = k [H^{+}]^{a}$
$100 = \frac{10^{- 2 a}}{10^{- 3 a}}$
$∴ α = 2$

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Similar questions

$Z n + 2 H^{+} \to Z n^{2 +} + H_{2}$

Half – life period is independent of concentration of constant pH. For the constant concentration of Zn, rate becomes 100 times when pH is decreased from 3 to 2. Hence,

Z n + 2 H^{\oplus} \to Z n^{2 +} + H_{2}

The half-life period is independent of the concentration of zinc at constant pH. For the constant concentration of Zn, the rate becomes 100 times when pH is decreased from 3 to 2. Hence:

Q. In acidic medium, the rate of reaction between

[B r O_{3}^{-}]

and

[B r^{-}]

ions is given by the expression

- \frac{d [B r O_{3}^{-}]}{d t} = k [B r O_{3}^{-}] [B r^{-}] [H^{+}]^{2}

It means:
(i) Rate constant of the reaction depends upon the concentration of

H^{+}

ions
(ii) Rate of reaction is independent of the concentration of acid added
(iii) The change in

p H

of the solution will affect the rate of reaction
(iv) Doubling the concentration of

H^{+}

ions will increase the reactions rate by

4

times.

Q. What

(H_{3} O^{+})

must be maintained in a saturated

H_{2} S

solution to precipitate

{P b}^{2 +}

, but not

{Z n}^{2 +}

from a solution in which each ion is present at a concentration of

0.01 M

?
(

K_{s p} H_{2} S = 1.1 \times 10^{- 22}

and

K_{s p} Z n S = 1.0 \times 10^{- 21}

)

Q. Maximum

p H

that must be maintained in a saturated

H_{2} S

(0.1 M) to precipitate

C d S

but not

Z n S

x

and concentration of

C d^{2 +}

ion at that

p H

y \times 10^{- 7}

then

x + y =

Given

[C d^{2 +}] = [{Z n}^{2 +}] = 0.1 M

initially

K_{s p} (C d S) = 8 \times 10^{- 27}

K_{s p} (Z n S) = 1 \times 10^{- 21}

K_{a 1} (H_{2} S) = 1.0 \times 10^{- 8}

K_{a 2} (H_{2} S) = 1.0 \times 10^{- 13}

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Zn+2H+→Zn2++H2Half-life period is independent of the concentration of zinc at constant pH. For the constant concentration of Zn, the rate becomes 100 times when pH is decreased from 3 to 2. Hence:

$Z n + 2 H^{+} \to Z n^{2 +} + H_{2}$
Half-life period is independent of the concentration of zinc at constant pH. For the constant concentration of Zn, the rate becomes 100 times when pH is decreased from 3 to 2. Hence: