Redox Reactions Chapter-Wise Test 13

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the oxidation number of sulfur in \( \ce{S2O3^2-} \)?

Let S = \( x \). O = -2. Equation: \( 2x + 3(-2) = -2 \), \( 2x - 6 = -2 \), \( 2x = 4 \), \( x = +2 \) (average).

+6
+2
+4
-2
2

Which reaction demonstrates reduction by the removal of oxygen from a metal oxide without hydrogen involvement?

In \( \ce{PbO2 + C -> Pb + CO2} \), Pb (+4 in \( \ce{PbO2} \)) loses oxygen to become 0, reduced by C (0 to +4), no hydrogen present.

\( \ce{PbO2 + C -> Pb + CO2} \)
\( \ce{Fe2O3 + 3H2 -> 2Fe + 3H2O} \)
\( \ce{CuO + H2 -> Cu + H2O} \)
\( \ce{2H2O2 -> 2H2O + O2} \)
1

In the reaction \( \ce{Zn + CuSO4 -> ZnSO4 + Cu} \), which species is reduced?

Reduction involves gain of electrons. Here, \( \ce{Cu^2+} \) from \( \ce{CuSO4} \) gains 2 electrons to form \( \ce{Cu} \) (oxidation state 0), indicating reduction.

\( \ce{Cu^2+} \)
\( \ce{Zn} \)
\( \ce{SO4^2-} \)
\( \ce{Zn^2+} \)
1

In the reaction \( \ce{2Cr + 3CuCl2 -> 2CrCl3 + 3Cu} \), which species is reduced?

Reduction involves electron gain. Cu (+2 in \( \ce{CuCl2} \)) gains electrons to become Cu (0).

\( \ce{Cu} \)
\( \ce{Cr} \)
\( \ce{CrCl3} \)
\( \ce{CuCl2} \)
1

In the reaction \( \ce{I2 + 5Cl2 + 6H2O -> 2HIO3 + 10HCl} \), how many electrons are transferred per iodine atom?

I (0 in \( \ce{I2} \)) becomes +5 in \( \ce{HIO3} \). Per I atom: 0 to +5 = 5 electrons.

2
3
6
5
4

In the reaction \( \ce{2KI + H2O2 -> I2 + 2KOH} \), which species acts as the oxidizing agent?

The oxidizing agent is reduced. \( \ce{H2O2} \) (O: -1) gains electrons to form \( \ce{OH^-} \) (O: -2), oxidizing \( \ce{I^-} \) to \( \ce{I2} \).

\( \ce{H2O2} \)
\( \ce{KI} \)
\( \ce{I2} \)
\( \ce{KOH} \)
1

What is the oxidation number of technetium in \( \ce{Tc2O7} \)?

Let Tc = \( x \). O = -2. Equation: \( 2x + 7(-2) = 0 \), \( 2x - 14 = 0 \), \( x = +7 \).

+5
+7
+6
+4
2

Which reaction involves the addition of oxygen to a metal?

In \( \ce{4Na + O2 -> 2Na2O} \), Na gains oxygen to form \( \ce{Na2O} \), an oxidation process.

\( \ce{2H2O -> 2H2 + O2} \)
\( \ce{Fe + H2SO4 -> FeSO4 + H2} \)
\( \ce{4Na + O2 -> 2Na2O} \)
\( \ce{2KClO3 -> 2KCl + 3O2} \)
3

What is the change in oxidation number of sulfur in the reaction \( \ce{2H2S + O2 -> 2S + 2H2O} \)?

S (-2 in \( \ce{H2S} \)) becomes 0 in \( \ce{S} \). Change = 0 - (-2) = +2.

+4
+2
-2
+6
2

What is the oxidation number of phosphorus in \( \ce{PCl3} \)?

Let P = \( x \). Cl = -1. Equation: \( x + 3(-1) = 0 \), \( x - 3 = 0 \), \( x = +3 \).

+5
+3
-3
+1
2

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