Electrochemistry Test

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Electrochemistry Test - 37

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Weekly Quiz Competition

Question 1
1 / -0

Electrolysis of water to form hydrogen and oxygen gas is called __________.

A
precipitation

B
oxidation-reduction

C
distillation

D
hydration

E
condensation

Solution

Electrolysis of water to form hydrogen and oxygen gas is called oxidation-reduction.
$$\displaystyle 2H_2O \rightarrow 2H_2 + O_2$$
Hydrogen ions (protons) are reduced.
$$\displaystyle 2H^+ + 2e^- \rightarrow H_2 $$
Hydroxide ions are oxidised.
$$\displaystyle 4OH^- \rightarrow 2H_2O + O_2 + 4e^-$$
Question 2
1 / -0

A battery jar contained a solution of copper sulfate. Two electrodes. one made of copper the other a metal object to be copper plated, were placed in the jar and connected to a source of direct current. Which of the following statements concerning this system is correct?

A
The object to be placed is the anode

B
Oxidation occurs at the anode

C
The sulfate ions migrate toward the cathode

D
The concentration of the copper sulfate solution increases as electrolysis proceeds

E
The copper electrode increases in mass.

Solution

In electrolytic cell, for $$Cu^{2+}$$ ions to get deposited at metal, metal sould have negative charge, i.e. it should act as cathode. Oxidation always occurs at anode. Sulphate ions will migrate towards anode as anode will have positive charge. Concentration of $$CuSO_4$$ decreases as electrolysis proceeds and the copper electrode decreases in mass.
Question 3
1 / -0

In the electrolysis of molten copper chloride, the substance liberated at the anode is __________ .

A
copper

B
chlorine

C
hydrogen

D
copper chloride

E
none of the above

Solution

In the electrolysis of molten copper chloride, the substance liberated at the anode is chlorine and the substance deposited at cathode is copper.
Oxidation at anode:
$$\displaystyle 2Cl^-(aq) \rightarrow Cl_2(g) + 2e^-$$
Reduction at cathode:
$$\displaystyle Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$$
Question 4
1 / -0

In the electrochemical cell shown above, which of the following half-reactions occurs at the anode?

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

B
$$\displaystyle Zn\left( s \right) \rightarrow { Zn }^{ 2+ }+2e$$

C
$$\displaystyle { Zn }^{ 2+ }+2e\rightarrow Zn\left( s \right) $$

D
$$\displaystyle Cu\left( s \right) \rightarrow { Cu }^{ 2+ }+2e$$

E
$$\displaystyle { Cu }^{ 2+ }+2e\rightarrow Cu\left( s \right) $$
$$\displaystyle $$

Solution

At anode, oxidation will take place and $$Zn(s)$$ will get oxidised to $$Zn^{2+}$$ leaving negatively charged electrons, making anode negatively charged, repelling negatively charged $$NO_3^-$$.
Question 5
1 / -0

Which of these half-reactions represents an oxidation?
I. $$Sn^{4+} \rightarrow Sn^{2+}$$
II. $$MnO_4^-\rightarrow Mn^{2+}$$
III. $$Cl_2\rightarrow ClO_3^-$$

A
I only

B
II only

C
III only

D
I and II only

E
II and III only

Solution

Oxidation state of $$Sn$$ changes from $$+4$$ to $$+2$$
Oxidation state of $$Mn$$ changes from $$+7$$ to $$+2$$
Oxidation state of $$Cl$$ changes from $$0$$ to $$+7$$

Therefore reaction $$III$$ represents oxidation.
Question 6
1 / -0

An iron nail, solid iron metal, rusts. What type of reaction is it?

A
Decomposition

B
Synthesis

C
Combustion

D
Single replacement

Solution

$$2Fe+O_2\rightarrow FeO$$ (rust)
Two compounds produce a single compound by reacting with each other. This is called as a synthesis reaction by the definition of synthesis reaction.
Question 7
1 / -0

$$Zn(s) | ZnCl_{2}(aq) | | Cl^{-}(aq)|Cl_{2}(g)|C(s)$$
In the electrochemical cell described by the cell diagram above, what reaction occurs at the anode?

A
$$Zn \rightarrow Zn^{2+} + 2e$$

B
$$Zn^{2+} + 2e\rightarrow Zn$$

C
$$Cl_{2} + 2e \rightarrow 2Cl^{-}$$

D
$$2C^{-}\rightarrow Cl_{2} + 2e$$

E
$$Zn + Cl_{2}\rightarrow ZnCl_{2}$$

Solution

At anode oxidation will take place and the anode reaction can be written as:
Oxidation reaction: $$Zn\rightarrow Zn^{2+}+2e^-$$
Question 8
1 / -0

A secondary cell is one that :

A
can be recharged

B
can be recharged by passing current through it in the same direction

C
can be recharged by passing current through it in the opposite direction

D
can not be recharged

Solution

A secondary cell is a type of cell which can be recharged (i.e storage battery) by passing cuurent through it in the opposite direction once the cell is discharged. Example: nickel – cadmium storage cell.
Question 9
1 / -0

In the galvanic cell :
$$Zn/Zn^{2+} (C_1)||Cu^{2+} (C_2)/Cu$$
$$E_{cell} - E_{cell}^o = +0.0591 V$$. The value of $$\dfrac{C_1}{C_2}$$ at $$298\ K$$ is:

A
$$10^{-1}$$

B
$$10^{2}$$

C
$$10^{-2}$$

D
$$10$$

Solution

$$\displaystyle E_{cell} - E_{cell}^o = +0.0591 V$$
$$\displaystyle E_{cell} = E_{cell}^o +0.0591 V$$
But
$$\displaystyle E_{cell} = E_{cell}^o - \dfrac {0.0591}{n} log \dfrac {C_1}{C_2} $$
Hence,
$$\displaystyle +0.0591 = - \dfrac {0.0591}{2} log \dfrac {C_1}{C_2}$$
$$\displaystyle log \dfrac {C_1}{C_2} =-2$$
$$\displaystyle \dfrac {C_1}{C_2} = 10^{-2}$$
Hence, option (C) is the correct answer.
Question 10
1 / -0

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

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

Electrochemistry Test - 37

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Electrochemistry Test - 37

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Question 1

precipitation

oxidation-reduction

distillation

hydration

condensation

Solution

Question 2

The object to be placed is the anode

Oxidation occurs at the anode

The sulfate ions migrate toward the cathode

The concentration of the copper sulfate solution increases as electrolysis proceeds

The copper electrode increases in mass.

Solution

Question 3

copper

chlorine

hydrogen

copper chloride

none of the above

Solution

Question 4

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

$$\displaystyle Zn\left( s \right) \rightarrow { Zn }^{ 2+ }+2e$$

$$\displaystyle { Zn }^{ 2+ }+2e\rightarrow Zn\left( s \right) $$

$$\displaystyle Cu\left( s \right) \rightarrow { Cu }^{ 2+ }+2e$$

$$\displaystyle { Cu }^{ 2+ }+2e\rightarrow Cu\left( s \right) $$$$\displaystyle $$

Solution

Question 5

I only

II only

III only

I and II only

II and III only

Solution

Question 6

Decomposition

Synthesis

Combustion

Single replacement

Solution

Question 7

$$Zn \rightarrow Zn^{2+} + 2e$$

$$Zn^{2+} + 2e\rightarrow Zn$$

$$Cl_{2} + 2e \rightarrow 2Cl^{-}$$

$$2C^{-}\rightarrow Cl_{2} + 2e$$

$$Zn + Cl_{2}\rightarrow ZnCl_{2}$$

Solution

Question 8

can be recharged

can be recharged by passing current through it in the same direction

can be recharged by passing current through it in the opposite direction

can not be recharged

Solution

Question 9

$$10^{-1}$$

$$10^{2}$$

$$10^{-2}$$

$$10$$

Solution

Question 10

$$1.69\ V + 0.76\ V$$

$$1.69\ V - 0.76\ V$$

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

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

Solution

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$$\displaystyle { Cu }^{ 2+ }+2e\rightarrow Cu\left( s \right) $$
$$\displaystyle $$