Redox Reactions Test

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Redox Reactions Test - 31

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Weekly Quiz Competition

Question 1
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Your group was asked to identify which types of reactions can be represented as redox reactions. Everyone has given an examples of what they think is correct.
Check their answer and decide who is right.

A
Crystal Lynn says synthesis reactions can be classified as redox: $$Na_{(s)} + Cl_{2(g)} \rightarrow 2NaCl_{(s)}$$

B
Barry Um says decomposition reactions can be classified as redox: $$H_{2}O_{(l)}\rightarrow H_{2(g)} + O_{2(g)}$$

C
Barry's brother, Cal C. Um states that single replacement reactions can be classified as redox: $$Ag_{(s)} + NaCl_{(aq)} \rightarrow Na_{(s)} + AgCl_{(aq)}$$

D
Molly Cule state everyone in the group is correct. Redox reactions can be classified as each of the examples cited.

Solution

$$Crystal$$ $$Lynn$$ is correct because,
$$2Na_{(s)}+{Cl_2}_{(g)}\longrightarrow 2NaCl_{(s)}$$ is a redox reaction.
Oxidation state of $$Na$$ and $$Cl$$ in reactant side is is $$0$$.
Because they are in free state.
But in right side, $$Na$$ is in $$+1$$ state and $$Cl$$ is in $$-1$$ state.
$$Na$$ changed from $$0$$ to $$+1\Longrightarrow Oxidised$$
$$Cl$$ changed from $$0$$ to $$-1\Longrightarrow Reduced$$
Oxidation and reduction, both occured in a reaction. So, it is a redox reaction.
Question 2
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$$I$$. The oxidation state of carbon in the compounds $${CH}_{4},{C}_{2}{H}_{6}$$ and $${C}_{2}{H}_{2}$$ is $$+4$$.
$$II$$. Carbon has four valence electrons.

A
Statement $$I$$ is true, Statement $$II$$ is true

B
Statement $$I$$ is true, Statement $$II$$ is false

C
Statement $$I$$ is false, Statement $$II$$ is true

D
Statement $$I$$ is false, Statement $$II$$ is false

Solution

$$I.$$ For covalent compounds, there is no oxidation state.
$$II.$$ Carbon has $$4$$ valence electrons. see the figure.
Question 3
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What is the oxidation number of $$Br$$ in the compound $$RbBr{O}_{4}$$?

A
$$-1$$

B
$$+7$$

C
$$+1$$

D
$$+4$$

Solution

$$RbBrO_4$$
Total charge$$=0.$$
$$Rb$$ is a $$group$$ $$I$$ element. So, its oxidation no. $$=+1$$.
Oxidation no. of oxygen $$=-2$$.
Let, Oxidation no. of $$Br$$ be $$x$$.
So, $$1+x+4(-2)=0\\1+x-8=0\\x-7=0\\x=7 $$
So, oxidation state of $$Bromine$$ is $$+7$$.
Question 4
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Balanced chemical equation imply which of the following?

A
Numbers of atoms are conserved in a chemical change

B
Numbers of molecules are conserved in a chemical change

C
Volume is conserved in a chemical change

D
'A' and 'B'

E
'B' and 'C'

Solution

In a balanced decimal equation, no. of atoms are conversed. Means, no. of atoms before reaction are exactly same as no. of atoms after reaction.
Question 5
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In which of the following compounds does nitrogen have the highest oxidation number?

A
Nitrogen Gas

B
Aluminum Nitride

C
Potassium Nitrate

D
Nitrous Acid

Solution

In Nitrogen gas, oxidation no. of Nitrogen is $$0$$. Because , it exist in free state.
In Aluminium Nitrate, it is $$-3\Longrightarrow AlN\Longrightarrow +3+x=0=-3.$$
In Potassium Nitrate, $$KNO_3\Longrightarrow 1+x+3(-2)=0=+5$$ .
In $$HNO_2$$ $$\Longrightarrow 1+x+2(-2)=0,\\x-3=0,\\x=3. $$
So, highest oxidation no. is in Potassium nitrate.
Question 6
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Which of the following is not a redox reaction?

A
$$3HCl(aq) + Na_{3}PO_{4}(aq) \rightarrow H_{3}PO_{4}(aq) + 3NaCl(aq)$$

B
$$CO(g) + H_{2}O(g)\rightarrow CO_{2}(g) + H_{2}(g)$$

C
$$Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)$$

D
$$4Ag(s) + 2H_{2}S(g) + O_{2}(g)\rightarrow 2H_{2}O(g) + 2Ag_{2}S(s)$$

Solution
Question 7
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$$2Pb{ O }_{ \left( s \right) }+{ C }_{ \left( s \right) }\rightarrow 2{ Pb }_{ \left( s \right) }+C{ O }_{ 2\left( g \right) }$$
Which of the following statements are correct for the above chemical reaction?
a) Lead is reduced
b) Carbon dioxide is oxidized
c) Carbon is oxidized
d) Lead oxide is reduced

A
(a) and (b)

B
(a) and (c)

C
(a), (b) and (c)

D
All

Solution

$$2PbO_{(s)}+C_{(s)}\longrightarrow 2Pb_{(s)}+CO_{2(g)}$$
$$\therefore$$ $$C$$ is oxidized from $$0$$ to $$+4$$ and $$Pb$$ is reduced from $$+2$$ to $$0.$$
Correct answer $$(a)$$ and $$(c).$$
Question 8
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Which expression gives the correct value for the standard potential for a gold-rhodium voltaic cell?
Half-reaction $$E^{\circ}(V)$$
$$Rh_{(aq)}^{+3} + 3e^{-} \rightarrow Rh_{(s)}$$ $$0.76\ V$$
$$Au_{(aq)}^{+} + e^{-} \rightarrow Au_{(s)}$$ $$1.69\ V$$

A
$$1.69\ V + 0.76\ V$$

B
$$1.69\ V - 0.76\ V$$

C
$$3(1.69)\ V + 0.76\ V$$

D
$$3(1.69)\ V - 0.76\ V$$

Solution

We know that, metal having higher reduction potential undergoes reduction;
so, Au will undergo reduction and Rh will undergo oxidation.
$$E^0_{cell}$$ = 1.69 V - 0.76 V
Question 9
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Which of the following represents the oxidation half-reaction for the unbalanced redox equation?
$$Cu + HNO_{3} \rightarrow Cu (NO_{3})_{2} + NO_{2}$$

A
$$Cu^{2+} + 2e^{-} \rightarrow Cu$$

B
$$Cu \rightarrow Cu^{2+} + 2e^{-}$$

C
$$NO_{3}^{-} \rightarrow NO_{2} + 1e^{-}$$

D
$$2H^{+} + NO_{2}^{-} + 1e^{-} \rightarrow NO_{2} + H_{2}O$$

Solution

$$Cu+HNO_3 \longrightarrow Cu(NO_3)_2+NO_2$$
As Oxidation of $$Cu$$ is taking place in the reaction.
Thus the oxidation half-cell reaction will be $$Cu \longrightarrow Cu^{+2}+2e^-$$
Question 10
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The given figure represents a $$Zn-Cu$$ electrochemical cell:
Based on the figure, which of the following represents the balanced chemical reaction?

A
$$Zn_{(aq)}^{2+} + Cu_{(s)} \rightarrow Zn_{(s)} + Cu_{(aq)}^{2+}$$

B
$$Zn_{(s)} + Cu_{(aq)}^{2+} \rightarrow Zn_{(aq)}^{2+} + Cu_{(s)}$$

C
$$Zn_{(s)} + Cu_{(s)} \rightarrow Zn_{(aq)}^{2+} + Cu_{(aq)}^{2+}$$

D
$$Zn_{(aq)}^{2+} + Cu_{(aq)}^{2+} \rightarrow Zn_{(s)} + Cu_{(s)}$$

Solution

$$Zn_{(s)}+Cu^{+2}_{(aq.)} \longrightarrow Zn^{+2}_{(aq.)}+Cu_{(s)}$$
$$\longrightarrow$$ This is also called Galvanic cell reaction.
$$\longrightarrow$$ In this $$Cu^{+2}$$ converts to $$Cu$$ due to high standard reduction potentials than $$Zn$$.

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Half-reaction	$$E^{\circ}(V)$$
$$Rh_{(aq)}^{+3} + 3e^{-} \rightarrow Rh_{(s)}$$	$$0.76\ V$$
$$Au_{(aq)}^{+} + e^{-} \rightarrow Au_{(s)}$$	$$1.69\ V$$

Redox Reactions Test - 31

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Redox Reactions Test - 31

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SHARING IS CARING

Question 1

Crystal Lynn says synthesis reactions can be classified as redox: $$Na_{(s)} + Cl_{2(g)} \rightarrow 2NaCl_{(s)}$$

Barry Um says decomposition reactions can be classified as redox: $$H_{2}O_{(l)}\rightarrow H_{2(g)} + O_{2(g)}$$

Barry's brother, Cal C. Um states that single replacement reactions can be classified as redox: $$Ag_{(s)} + NaCl_{(aq)} \rightarrow Na_{(s)} + AgCl_{(aq)}$$

Molly Cule state everyone in the group is correct. Redox reactions can be classified as each of the examples cited.

Solution

Question 2

Statement $$I$$ is true, Statement $$II$$ is true

Statement $$I$$ is true, Statement $$II$$ is false

Statement $$I$$ is false, Statement $$II$$ is true

Statement $$I$$ is false, Statement $$II$$ is false

Solution

Question 3

$$-1$$

$$+7$$

$$+1$$

$$+4$$

Solution

Question 4

Numbers of atoms are conserved in a chemical change

Numbers of molecules are conserved in a chemical change

Volume is conserved in a chemical change

'A' and 'B'

'B' and 'C'

Solution

Question 5

Nitrogen Gas

Aluminum Nitride

Potassium Nitrate

Nitrous Acid

Solution

Question 6

$$3HCl(aq) + Na_{3}PO_{4}(aq) \rightarrow H_{3}PO_{4}(aq) + 3NaCl(aq)$$

$$CO(g) + H_{2}O(g)\rightarrow CO_{2}(g) + H_{2}(g)$$

$$Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)$$

$$4Ag(s) + 2H_{2}S(g) + O_{2}(g)\rightarrow 2H_{2}O(g) + 2Ag_{2}S(s)$$

Solution

Question 7

(a) and (b)

(a) and (c)

(a), (b) and (c)

All

Solution

Question 8

$$1.69\ V + 0.76\ V$$

$$1.69\ V - 0.76\ V$$

$$3(1.69)\ V + 0.76\ V$$

$$3(1.69)\ V - 0.76\ V$$

Solution

Question 9

$$Cu^{2+} + 2e^{-} \rightarrow Cu$$

$$Cu \rightarrow Cu^{2+} + 2e^{-}$$

$$NO_{3}^{-} \rightarrow NO_{2} + 1e^{-}$$

$$2H^{+} + NO_{2}^{-} + 1e^{-} \rightarrow NO_{2} + H_{2}O$$

Solution

Question 10

$$Zn_{(aq)}^{2+} + Cu_{(s)} \rightarrow Zn_{(s)} + Cu_{(aq)}^{2+}$$

$$Zn_{(s)} + Cu_{(aq)}^{2+} \rightarrow Zn_{(aq)}^{2+} + Cu_{(s)}$$

$$Zn_{(s)} + Cu_{(s)} \rightarrow Zn_{(aq)}^{2+} + Cu_{(aq)}^{2+}$$

$$Zn_{(aq)}^{2+} + Cu_{(aq)}^{2+} \rightarrow Zn_{(s)} + Cu_{(s)}$$

Solution

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