Redox Reactions Test

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Redox Reactions Test - 24

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Weekly Quiz Competition

Question 1
1 / -0

Out of the following, select species with different oxidation states of the underlined atoms.
$$I:CaO\underline { { Cl }_{ 2 } } $$;
$$II:{ H }_{ 2 }\underline { { S }_{ 2 } } { O }_{ 8 }$$;
$$III:{ Na }_{ 2 }\underline { { S }_{ 4 } } { O }_{ 6 }$$;
$$IV:Cr\underline { { O }_{ 5 } } $$;
$$V:\underline { { N }_{ 2 } } { H }_{ 4 }{ O }_{ 3 }$$

A
All except I

B
All except II

C
All except III

D
All except IV

Solution

$$V:\underset { -3 }{ { NH }_{ 4 }^{ + } } \quad \quad \underset { +5 }{ N } { O }_{ 3 }^{ - }$$
Question 2
1 / -0

Bleaching powder ($$CaO{Cl}_{2}$$) has two types of chlorine atoms with oxidation number of $$+1$$ and $$-1$$. It can be represented as :

A
$${ Ca }^{ 2+ }\left( Cl{ O }_{ 2 }^{ - } \right) { Cl }^{ - }$$

B
$${ Ca }^{ 2+ }\left( Cl{ O }_{ 3 }^{ - } \right) { Cl }^{ - }$$

C
$${ Ca }^{ 2+ }\left( Cl{ O }_{ }^{ + } \right) { Cl }^{ - }$$

D
$${ Ca }^{ 2+ }\left( Cl{ O }_{ }^{ - } \right) { Cl }^{ - }$$

Solution

Bleaching powder has two types of Cl atoms with oxidation number of $$+1$$ and $$-1$$, one is directly attached to $$Ca$$ and other to oxygen. Therefore, it can be representated as $${ Ca }^{ 2+ }\left( Cl{ O }_{ }^{ - } \right) { Cl }^{ - }$$.
It has been shown in the structure below:
Question 3
1 / -0

$${ Fe }^{ 2+ }$$ is oxidised by $$Mn{ O }_{ 4 }^{ - }$$ or $${ Cr }_{ 2 }{ O }_{ 7 }^{ 2- }$$ in acidic medium. What is new oxidation number of Fe?

A
$$+3$$

B
$$+1$$

C
$$+2$$

D
$$+4$$

Solution

$$5{ Fe }^{ 2 }+\underset { pinkish\\ violet }{ Mn{ O }_{ 4 }^{ - } } +8{ H }^{ + }\longrightarrow \underset { colourless }{ { Mn }^{ 2+ } } +5{ Fe }^{ 3+ }+4{ H }_{ 2 }O\quad$$ ; $$\quad 6{ Fe }^{ 2+ }+\underset { orange }{ { Cr }_{ 2 }{ O }_{ 7 }^{ 2- } } +14{ H }^{ + }\longrightarrow 6{ Fe }^{ 3+ }+2{ Cr }^{ 3+ }+7{ H }_{ 2 }O$$
New oxidation state of iron is $$+3$$.
Question 4
1 / -0

Oxidation number of oxygen in superoxide ion, $${O}_{2}^{-}$$ is :

A
$$-2$$

B
$$-\cfrac{1}{2}$$

C
$$-\cfrac{3}{2}$$

D
none of these

Solution

Given superoxide ion, $${ O }_{ 2 }^{-}$$.
If oxidation number if oxygen $$=x$$
then, $$2x=-1$$
$$\therefore x=-\cfrac{1}{2}$$
Question 5
1 / -0

In $$\left[ Cr({ O }_{ 2 }){ \left( { NH }_{ 3 } \right)}_{ 4 }{ (H }_{ 2 }O) \right] { Cl }_{ 2 }$$, oxidation number of $$Cr$$ is $$+3$$ then, $${O}_{2}$$ will be in the form of :

A
dioxo

B
peroxo

C
superoxo

D
oxo

Solution

Let the oxidation number of $$O_2$$ be $$x$$.
Since the overall charge on the complex is $$0$$, the sum of oxidation states of all elements in it should be equal to $$0$$.
$$\left[ \underset { +3 }{ Cr } \underset { +x }{ ({ O }_{ 2 }) } \underset { +0 }{ { \left( { NH }_{ 3 } \right) }_{ 4 } } \underset { +0 }{ \left( { H }_{ 2 }O \right) } \right] \underset { -1 }{ { Cl }_{ 2 } } $$
Therefore, $$x+3+0+0-2 =0; x=-1$$
So, $$({O}_{2})$$ exists as $${ O }_{ 2 }^{ - }$$ (superoxide ion).
Question 6
1 / -0

What is the oxidation number of sulphur in $${ H }_{ 2 }{ S }_{ 2 }{ O }_{ 8 }$$?

A
+7

B
+5

C
+6

D
This compound does not exist

Solution

$${ H }_{ 2 }{ S }_{ 2 }{ O }_{ 8 }+2{ H }_{ 2 }O\longrightarrow 2{ H }_{ 2 }{ SO }_{ 4 }+{ H }_{ 2 }{ O }_{ 2 }$$
The structure of $${ H }_{ 2 }{ S }_{ 2 }{ O }_{ 8 }$$ has been given below:
We can see that it has a peroxide linkage in which each oxygen atom has oxidation number of $$-1$$.
Let $$x$$ be the oxidation state of S in $${ H }_{ 2 }{ S }_{ 2 }{ O }_{ 8 }$$.
Since the overall charge on the complex is $$0$$, the sum of oxidation states of all elements in it should be equal to $$0$$.
Therefore, $$+2+2x- 2(4)-2 -4 =0$$
or, $$x=+6$$
Question 7
1 / -0

Strongest conjugate base is :

A
$$Cl{ O }^{ - }$$

B
$$Cl{ O }_{ 2 }^{ - }$$

C
$$Cl{ O }_{ 3 }^{ - }$$

D
$$Cl{ O }_{ 4 }^{ - }$$

Solution

If acid is weak, its conjugate base is strong.
Greater the oxidation number of Cl, stronger the acid and thus, weaker the conjugate base.
Acid oxidation no of Cl conjugate base
$$HClO$$ +1 $$ClO^-$$
$$HClO_2$$    +3      $$ClO_2^-$$
$$HClO_3$$    +5        $$ClO_3^-$$
$$HClO_4$$ +7          $$ClO_4^-$$
As we move down the group, strength of acid increases while strength of base decreases, so strongest base is $$ClO^-$$.
Question 8
1 / -0

When $${Cl}^{-}$$ is converted into $${Cl}_{2}$$, change in oxidation number is :

A
$$3$$ units

B
$$1$$ units

C
$$2$$ units

D
none of these

Solution

The reaction is $$\underset { -1 }{ { Cl }^{ - } } \longrightarrow \cfrac { 1 }{ 2 } \underset { 0 }{ { Cl }_{ 2 } } $$
Change in oxidation number $$=1$$ unit.
Question 9
1 / -0

Prussian blue has two types of iron with oxidation number as shown below:
$$\overset { III }{ Fe } \left[ \overset { II }{ Fe } { \left( CN \right) }_{ 6 } \right] $$
What is the net charge on prussian blue?

A
$$-1$$

B
$$+1$$

C
$$0$$

D
$$-2$$

Solution

According to given conditions,
$$\overset { III }{ Fe } \left[ \overset { II }{ Fe } { \left( CN \right) }_{ 6 } \right] $$
Sum of the charges = $$+3+2-6\times 1 = -1$$.
Therefore, net charge on compound is $$-1$$.
Question 10
1 / -0

$${ H }_{ 2 }{ S }_{ 2 }{ O }_{ 8 }$$ and $${ H }_{ 2 }S{ O }_{ 5 }$$, both have $$+6$$ oxidation state of sulphur. It is due to the :

A
presence of peroxy group

B
presence of superoxo group

C
presence of neutral $${O}_{2}$$

D
presence of ozone

Solution

$${ H }_{ 2 }{ S }_{ 2 }{ O }_{ 8 }$$ and $${ H }_{ 2 }S{ O }_{ 5 }$$, both have $$+6$$ oxidation state of sulphur. It is due to the presence of peroxy group. Both peroxomonosulphuric acid and peroxodisulphuric acid contains 1 peroxy group each.

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Redox Reactions Test - 24

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Redox Reactions Test - 24

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Question 1

All except I

All except II

All except III

All except IV

Solution

Question 2

$${ Ca }^{ 2+ }\left( Cl{ O }_{ 2 }^{ - } \right) { Cl }^{ - }$$

$${ Ca }^{ 2+ }\left( Cl{ O }_{ 3 }^{ - } \right) { Cl }^{ - }$$

$${ Ca }^{ 2+ }\left( Cl{ O }_{ }^{ + } \right) { Cl }^{ - }$$

$${ Ca }^{ 2+ }\left( Cl{ O }_{ }^{ - } \right) { Cl }^{ - }$$

Solution

Question 3

$$+3$$

$$+1$$

$$+2$$

$$+4$$

Solution

Question 4

$$-2$$

$$-\cfrac{1}{2}$$

$$-\cfrac{3}{2}$$

none of these

Solution

Question 5

dioxo

peroxo

superoxo

oxo

Solution

Question 6

+7

+5

+6

This compound does not exist

Solution

Question 7

$$Cl{ O }^{ - }$$

$$Cl{ O }_{ 2 }^{ - }$$

$$Cl{ O }_{ 3 }^{ - }$$

$$Cl{ O }_{ 4 }^{ - }$$

Solution

Question 8

$$3$$ units

$$1$$ units

$$2$$ units

none of these

Solution

Question 9

$$-1$$

$$+1$$

$$0$$

$$-2$$

Solution

Question 10

presence of peroxy group

presence of superoxo group

presence of neutral $${O}_{2}$$

presence of ozone

Solution

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