Redox Reactions Test

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Redox Reactions Test - 62

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Question 1
1 / -0

In an experiment, $$50$$ mL of $$0.1$$ M solution of a metallic salt reacted exactly with $$25$$ mL of $$0.1$$ M solution of sodium sulphite. In the reaction, $${SO_3}^{-}$$ is oxidised to $${SO_4}^{2-}$$. If the original oxidation number of the metal in the salt was $$3$$, what would be the new oxidation number of the metal?

A
0

B
1

C
2.5

D
4

Solution

Total number of millimoles of metallic salt present $$= 50 mL \times 0.1 M = 5$$ millimoles.
Total number of millimoles of sodium sulphite $$= 25 mL \times 0.1 M = 2.5 $$ millimoles.
The oxidation number of S changes from +5 to +6.
Increase in the oxidation number of 1 S atom = 1.
Total number of millimoles electrons lost by sodium sulphite = 2.5
5 millimoles of metallic salt gains 2.5 millimoles of electrons.
1 molecule of metallic salt will gain 0.5 electron.
Hence, the oxidation number of metal will decrease from 3 to 2.5.
Question 2
1 / -0

The oxidation state of the most electronegative element in the products of the reaction between $$BaO_2$$ and $$H_2SO_4$$ is:

A
0 and -1

B
-1 and -2

C
-2 and 0

D
-2 and +1

Solution

Reaction between $$BaO_2$$ and $$H_2SO_4$$ is as follows:
$$BaO_2+H_2SO_4\rightarrow H_2O_2+BaSO_4$$
$$-1$$ $$-2$$
The most electronegative element is oxygen in both the products and its oxidation state is $$-1$$ and $$-2$$ respectively, in $$H_2O_2$$ and $$BaSO_4$$.
Question 3
1 / -0

The oxidation state of +3 for phosphorous is in :

A
hypophosphorous acie

B
meta-phosphoric acid

C
ortho-phosphoric acid

D
phosphorous acid

Solution

The oxidation state of +3 for phosphorous is in phosphorous acid.
The oxidation state of P in hypophosphorous acid +1, meta-phosphoric acid +5 and ortho-phosphoric acid +5
is +1, +5 and +5 respectively.
Question 4
1 / -0

The oxidation number of phosphorus in $$PO^{3-}_4, P_4O_{10}$$ and $$P_2O_7^{4-}$$ is:

A
+3

B
+2

C
-3

D
+5

Solution

The structure of $$PO^{3-}_4, P_4O_{10}$$ and $$P_2O_7^{4-}$$ are given below:
In ecah of these, the oxidation state of P is $$+5$$.
Question 5
1 / -0

Oxidation state of nitrogen is incorrectly given in which of the following compound?

A
$$[Co(NH_3)_5Cl]Cl_2$$, $$-3$$

B
$$NH_2OH$$, $$ -1$$

C
$$(N_2H_5)_2SO_4$$, $$+2$$

D
$$Mg_3N_2$$, $$-3$$

Solution

Let X be the oxidation state of N in $$\displaystyle (N_2H_5)_2SO_4 $$
$$\displaystyle 2(2X-5) -2 = 0 $$
$$\displaystyle 4X-12=0 $$
$$\displaystyle 4X = 12 $$
$$\displaystyle X = +3 $$
Hence, the oxidation state of N in $$\displaystyle (N_2H_5)_2SO_4 $$ is +3.
Question 6
1 / -0

The oxidation number of $$S$$ in $$Na_2S_4O_6$$ is :

A
$$+2.5$$

B
$$+2$$ and $$+3$$ (two $$S$$ have $$+2$$ and other two have $$+3$$)

C
$$+2$$ and $$+3$$ (three $$S$$ have $$+2$$ and one $$S$$ has $$+3$$)

D
$$+5$$ and $$0$$ (two S have $$+5$$ and the other two $$S$$ have $$0$$)

Solution

The oxidation number of $$S$$ in $$Na_2S_4O_6$$ is $$+5$$ and $$0$$ (two S have $$+5$$ and the other two $$S$$ have $$0$$)
Question 7
1 / -0

Which does not represent auto-redox process?

A
$$4CrO_5 + 6H_2SO_4 \rightarrow 2Cr_2(SO_4)_3+6H_2O+7O_2$$

B
$$2C_6H_5CHO \overset{Al(OC_2H_5)_3}{\rightarrow}C_6H_5COOCH_2C_6H_5$$

C
$$4KCIO_3\rightarrow 3KClO_4+KCI$$

D
$$CHO-CHO \xrightarrow {NaOH} CH_2OH-CHO + COOH-CHO$$

Solution

$$4CrO_5 + 6H_2SO_4 \rightarrow 2Cr_2(SO_4)_3+6H_2O+7O_2$$
$$+6$$ $$+3$$
So, its an intramolecular redox reaction.
Question 8
1 / -0

The brown ring complex, $$[Fe(H_2O)_5NO^+]SO_4$$ has oxidation number of Fe as :

A
+1

B
+2

C
+3

D
+4

Solution

$$NO$$ in brown ring complex has $$+1$$ oxidation state.
Let oxidation state of Fe be $$x$$.
Since the overall charge on the coordination sphere, $$[Fe(H_2O)_5NO^+]$$ is $$+2$$, the sum of oxidation states of all elements in it should be equal to $$+2$$.
Therefore, $$x+1 =+2$$
or, $$ x = +1$$
Hence, the oxidation state of iron in the brown ring complex is $$+1$$.
Question 9
1 / -0

The oxidation number of sulphur in $$S_8, S_2F_2$$ and $$H_2S$$ respectively, are :

A
$$0,\: +1$$ and $$-2$$

B
$$+2,\: +1$$ and $$-2$$

C
$$0,\: +1$$ and $$+2$$

D
$$-2,\: +1$$ and $$-2$$

Solution

The oxidation number of sulphur in $$S_8, S_2F_2$$ and $$H_2S$$ respectively, are $$0,\: +1$$ and $$-2$$
(1) Let x be the oxidation number of S in $$S_8$$.
$$\displaystyle 8X = 0 $$
$$\displaystyle X=0 $$
(2) Let x be the oxidation number of S in $$ S_2F_2$$
$$\displaystyle 2X -2 =0$$
$$\displaystyle X = +1 $$
(3) Let x be the oxidation number of S in $$H_2S$$
$$\displaystyle X+2=0 $$
$$\displaystyle X = -2$$
Question 10
1 / -0

Which combination appears odd with respect to oxidation number per atom of the underlined?

A
$${ H }_{ 2 }\underline { S } { O }_{ 5 },{ H }_{ 2 }\underline { S } { O }_{ 8 },{ K }_{ 2 }\underline { { Cr }_{ 2 } } { O }_{ 7 }$$

B
$$\underline { Cr } { O }_{ 5 },\underline { Cr } { O }_{ 4 }^{ 2- },S{ O }_{ 4 }^{ 2- }$$

C
Both (a) and (b)

D
None of the above

Solution

In all the given compounds central atom has oxidation state of +6.

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Redox Reactions Test - 62

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Redox Reactions Test - 62

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Question 1

0

1

2.5

4

Solution

Question 2

0 and -1

-1 and -2

-2 and 0

-2 and +1

Solution

Question 3

hypophosphorous acie

meta-phosphoric acid

ortho-phosphoric acid

phosphorous acid

Solution

Question 4

+3

+2

-3

+5

Solution

Question 5

$$[Co(NH_3)_5Cl]Cl_2$$, $$-3$$

$$NH_2OH$$, $$ -1$$

$$(N_2H_5)_2SO_4$$, $$+2$$

$$Mg_3N_2$$, $$-3$$

Solution

Question 6

$$+2.5$$

$$+2$$ and $$+3$$ (two $$S$$ have $$+2$$ and other two have $$+3$$)

$$+2$$ and $$+3$$ (three $$S$$ have $$+2$$ and one $$S$$ has $$+3$$)

$$+5$$ and $$0$$ (two S have $$+5$$ and the other two $$S$$ have $$0$$)

Solution

Question 7

$$4CrO_5 + 6H_2SO_4 \rightarrow 2Cr_2(SO_4)_3+6H_2O+7O_2$$

$$2C_6H_5CHO \overset{Al(OC_2H_5)_3}{\rightarrow}C_6H_5COOCH_2C_6H_5$$

$$4KCIO_3\rightarrow 3KClO_4+KCI$$

$$CHO-CHO \xrightarrow {NaOH} CH_2OH-CHO + COOH-CHO$$

Solution

Question 8

+1

+2

+3

+4

Solution

Question 9

$$0,\: +1$$ and $$-2$$

$$+2,\: +1$$ and $$-2$$

$$0,\: +1$$ and $$+2$$

$$-2,\: +1$$ and $$-2$$

Solution

Question 10

$${ H }_{ 2 }\underline { S } { O }_{ 5 },{ H }_{ 2 }\underline { S } { O }_{ 8 },{ K }_{ 2 }\underline { { Cr }_{ 2 } } { O }_{ 7 }$$

$$\underline { Cr } { O }_{ 5 },\underline { Cr } { O }_{ 4 }^{ 2- },S{ O }_{ 4 }^{ 2- }$$

Both (a) and (b)

None of the above

Solution

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