Redox Reactions Test

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Redox Reactions Test - 27

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Weekly Quiz Competition

Question 1
1 / -0

The oxidation number of phosphorous in $$P{ O }_{ 4 }^{ 3- },\ { P }_{ 4 }{ O }_{ 10 }$$ and $${ P }_{ 2 }{ O }_{ 7 }^{ 4- }$$ is :

A
$$+5$$

B
$$+3$$

C
$$-3$$

D
$$+2$$

Solution

The oxidation number of phosphorous in $$P{ O }_{ 4 }^{ 3- }, { P }_{ 4

}{ O }_{ 10 }$$ and $${ P }_{ 2 }{ O }_{ 7 }^{ 4- }$$ is +5.
Let X be the oxidation number of P in $$P{ O }_{ 4 }^{ 3- }$$.
$$\displaystyle X+4(-2) = -3 $$
$$\displaystyle X = +5$$
Let X be the oxidation number of P in$$ { P }_{ 4.

}{ O }_{ 10 }$$
$$\displaystyle 4X +10(-2) =0 $$
$$\displaystyle X = +5 $$
Let X be the oxidation number of P in$${ P }_{ 2 }{ O }_{ 7 }^{ 4- }$$.
$$\displaystyle 2X + 7(2-) =-4 $$
$$\displaystyle X =+5 $$
Question 2
1 / -0

The change in the oxidation number of the underlined nitrogen atom in the following chemical reactions are :
a. Nitrous acid $$\left( H\underline { N } { O }_{ 2 } \right)$$ reduces $$Mn{ O }_{ 4 }^{ \ominus }$$ in acid solution.
b. Nitrous acid $$\left( H\underline { N } { O }_{ 2 } \right)$$ oxidises $${ I }^{ \ominus }$$ to $${ I }_{ 2 }$$ in acid solution.

A
(a) +3 to +5
(b) +3 to +2

B
(a) +3 to +6
(b) +3 to +2

C
(a) +3 to +5
(b) +3 to +1

D
(a) +3 to +2
(b) +3 to +5

Solution

The balanced reactions are as follows:
i. $$2Mn{ O }_{ 4 }^{ \ominus } + 6{ H }^{ + } + 5N{ O }_{ 2 }^{ \ominus } \longrightarrow 5N{ O }_{ 3 }^{ \ominus } + 3{ H }_{ 2 }O + 2{ Mn }^{ 2+ }$$
ii. $$2HN{ O }_{ 2 } + 2{ H }^{ \oplus } + 2{ I }^{ \ominus } \longrightarrow 2NO + 2{ H }_{ 2 }O + { I }_{ 2 }$$
Oxidation number of $$N$$ changes from +3 to +5 in (i).
Oxidation number of $$N$$ changes from +3 to +2 in (ii).
Question 3
1 / -0

When $$kMnO_4$$ acts as an oxidising agent and ultimately forms $$MnO^{2-}_4,\ MnO_2,\, Mn_2O_3,$$ $$\, $$and$$\, Mn^{2+}$$, determine the number of electrons transferred in each case.

A
$$1,3,4,5$$

B
$$1,2,3,5$$

C
$$1,3,5,4$$

D
$$1,2,4,5$$

Solution

$$KMnO_4 \xrightarrow {1e^-} MnO_4^{2-}$$
$$KMnO_4 \xrightarrow {3e^-} MnO_2$$
$$KMnO_4 \xrightarrow {4e^-} Mn_2O_3$$
$$KMnO_4 \xrightarrow {5e^-} Mn^{2+}$$
Question 4
1 / -0

The oxidation state of manganese in $${K}_{2}Mn{O}_{4}$$ is:

A
$$+5$$

B
$$+6$$

C
$$+4$$

D
$$+7$$
Question 5
1 / -0

The oxidation number of sulphur in $${H}_{2}{SO}_{4}$$ is :

A
$$4$$

B
$$2$$

C
$$6$$

D
Zero

Solution

For a compound $${H}_{2} \mathrm{SO}_{4}$$,

As net charge on compound is $$0$$
Charge on : $$H =1$$
$$~~~~~~~~~~~~~~~~~~~~S =x$$
$$~~~~~~~~~~~~~~~~~~~~O =-2$$
$$1(2)+x+(-2)(4)=0$$
$$2+x-8=0$$
$$x=6$$

Hence, option C is correct.
Question 6
1 / -0

Oxidation number of $$S$$ in $${S_2O_3}^{2-}$$ is:

A
-2

B
+2

C
+6

D
0

Solution

Let Oxidation number of S in $$S_2O_3^{2-}$$ be x.
Thus,
2x+(-2*3)= -2
2x-6= -2
2x= -2+6
2x=4
x=4\2
x=2
so the oxidation state of sulfur is +2
Question 7
1 / -0

Which of the following does not represent redox reaction?

A
$$Cr_2O^{2-}_7\,+\,2 OH^-\,\rightarrow\, 2CrO^{2-}_4\,+\,H_2O$$

B
$$SO^{2-}_5\,+\, I^-\,\rightarrow\, I_2\,+\,SO^{2-}_4$$

C
$$Ca(OH)_2\,+\, Cl_2\,\rightarrow\, Ca(OCl)_2\,+\,CaCl_2$$

D
$$PCl_5\,\rightarrow\,PCl_3\,+\,Cl_2$$

Solution

$$Cr_2O^{2-}_7\,+\,2 OH^-\,\rightarrow\, 2CrO^{2-}_4\,+\,H_2O$$
Above reaction represents redox reaction since it does not undergoes oxidation or reduction.
Question 8
1 / -0

Determine oxidation number of iron in $$Na_2[Fe(CN)_5(NO)]$$.

A
+ 2

B
+3

C
+1

D
+4

Solution

$$CN$$ has a charge of $$-1$$, $$NO$$ is $$0$$, and $$Na$$ is $$+1$$. This makes $$Fe\ +3$$, since it has to combine with the overall $$+2$$ from the sodium ions to balance the overall $$-5$$ from the cyanide groups.

$$2 \times (+1) +x + 5 \times (-1) + 0= 0$$

$$x=+3$$

Option B is correct.
Question 9
1 / -0

Determine the oxidation state of Cr in $$[Cr(NH_3)_4Cl_2]Cl$$

A
+ 3

B
-3

C
+2

D
+4

Solution

$$NH_3$$ is 0
each $$Cl$$ inside the brackets is -1
the final $$Cl$$ is -1
sooxidation staate of $$Cr$$ is +3.
Question 10
1 / -0

In $$\displaystyle HCN$$ oxidation number of carbon is?

A
+2

B
+3

C
+4

D
+1

Solution

$$HCN =H^+ + CN^{-}$$

$$x-3=-1$$

$$x=-1+3$$

$$x=+2$$

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Redox Reactions Test - 27

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Redox Reactions Test - 27

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Question 1

$$+5$$

$$+3$$

$$-3$$

$$+2$$

Solution

Question 2

(a) +3 to +5(b) +3 to +2

(a) +3 to +6(b) +3 to +2

(a) +3 to +5(b) +3 to +1

(a) +3 to +2(b) +3 to +5

Solution

Question 3

$$1,3,4,5$$

$$1,2,3,5$$

$$1,3,5,4$$

$$1,2,4,5$$

Solution

Question 4

$$+5$$

$$+6$$

$$+4$$

$$+7$$

Question 5

$$4$$

$$2$$

$$6$$

Zero

Solution

Question 6

-2

+2

+6

0

Solution

Question 7

$$Cr_2O^{2-}_7\,+\,2 OH^-\,\rightarrow\, 2CrO^{2-}_4\,+\,H_2O$$

$$SO^{2-}_5\,+\, I^-\,\rightarrow\, I_2\,+\,SO^{2-}_4$$

$$Ca(OH)_2\,+\, Cl_2\,\rightarrow\, Ca(OCl)_2\,+\,CaCl_2$$

$$PCl_5\,\rightarrow\,PCl_3\,+\,Cl_2$$

Solution

Question 8

+ 2

+3

+1

+4

Solution

Question 9

+ 3

-3

+2

+4

Solution

Question 10

+2

+3

+4

+1

Solution

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(a) +3 to +5
(b) +3 to +2

(a) +3 to +6
(b) +3 to +2

(a) +3 to +5
(b) +3 to +1

(a) +3 to +2
(b) +3 to +5