[2 Mark Question Answer]

Question 12 Marks

State the observation at the anode and at the cathode during the electrolysis of :
Copper sulphate solution using copper electrodes.

Answer

Observations:
Anode : Nothing gets deposited on the anode because the copper anode dissolves during the reaction as $Cu^{2+}$ ions are formed.
Cathode : Reddish brown Cu is deposited.

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Question 22 Marks

State the observation at the anode and at the cathode during the electrolysis of :
Fused lead bromide using graphite electrodes

Answer

Observations:
Anode: Dark reddish brown fumes of bromine evolve at the anode.
Cathode: Greyish white metal lead is formed on the cathode.

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Question 32 Marks

Give reason why:
Although copper is a good conductor of electricity, it is a non-electrolyte.

Answer

Copper has no mobile electrons in the solid state and an electrolyte should dissociate into oppositely charged ions to conduct electricity.
Hence, copper is a non-electrolyte.

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Question 42 Marks

Give reason why:
In the electroplating of an article with silver, the electrolyte sodium argento-cynide solution is preferred over silver nitrate solution.

Answer

If silver nitrate solution is used directly instead of double cyanide of silver and sodium, the deposition of silver will be very fast and hence not very smooth and uniform.

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Question 52 Marks

Give reason why:
Sodium chloride will conduct electricity only in fused or aqueous solution state.

Answer

Electrostatic forces of attraction between ions in the solid state are very strong. These forces weaken in the fused state or in the solution state. Hence, ions become mobile.

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Question 62 Marks

Write the equation taking place at the anode.

Answer

$Ag - e^- → Ag^+$
$Cu - e- → Cu^{2+}$
$Cl^⁻‒ e^-→ Cl$
$Cl + Cl → Cl_2$

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Question 72 Marks

Copy and complete the following table :

	Anode	Electrolyte
Purification of copper

Answer

	Anode	Electrolyte
Purification of copper	Impure copper	Solution of copper sulphate and dilute sulphuric acid

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Question 82 Marks

Give appropriate scientific reasons for the following statement :
Electrolysis of molten lead bromide is considered to be a redox reaction.

Answer

During electrolysis of lead bromide, there is loss of electrons at the anode by bromine and gain of electrons at the cathode by lead. Thus, oxidation and reduction occur side by side. So, it is a redox reaction. $PbBr_2⇌ Pb^{+2}+ 2Br^-$

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Question 92 Marks

Give appropriate scientific reasons for the following statement :
The electrical conductivity of acetic acid is less in comparision to the electrical conductivity of dilute sulphuric acid at a given concentration.

Answer

Acetic acid is a weak acid and has fewer ions, so conductivity is less, whereas dilute sulphuric acid is a strong acid and has more ions, and therefore, its electrical conductivity is more.

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Question 102 Marks

Give appropriate scientific reasons for the following statement :
During electrolysis of molten lead bromide graphite anode is preferred to other electrodes.

Answer

In electrolysis of molten lead bromide, reactive bromine is liberated at the anode. As bromine is very reactive, an inert electrode like graphite is preferred in the electrolysis of molten lead bromide.

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Question 112 Marks

Give appropriate scientific reasons for the following statement :
Carbon tetrachloride does not conduct electricity.

Answer

Carbon tetrachloride is a liquid and does not conduct electricity because it is a covalent compound and there are no free ions present and it contains only molecules.

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Question 122 Marks

Give appropriate scientific reasons for the following statement :
Zinc oxide can be reduced to zinc by using carbon monoxide, but aluminium oxide cannot be reduced by a reducing agent.

Answer

Zinc is lower in the reactivity series, so it is comparatively less reactive. Hence, it is reduced by using carbon monoxide. But aluminium is very reactive; hence, it cannot be reduced by using a reducing agent and it can be reduced only by electrolytic reduction.

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Question 132 Marks

Aqueous solution of nickel sulphate contains $Ni ^{+2}$ and $SO _4^{-2}$ ions.
(a) Which ion moves towards the cathode?
(b) What is the product at the anode?

Answer

(a) Nickel ions move towards cathode.
(b) Nickel ions.

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Question 142 Marks

Correct the following statement:
Lead bromide conducts electricity.

Answer

Molten Lead bromide conducts electricity.

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Question 152 Marks

A solution of silver nitrate is a good electrolyte but is not used for electroplating an article with silver.

Answer

A solution of silver nitrate is good electrolyte but is not used for electroplat ing an article with silver because, the deposition of silver will be very fast and hence not smooth and uniform.

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Question 162 Marks

Study the diagram given alongside and answer the questions that follow :

(i) Give the names of the electrode A and B.
(ii) Which electrode is oxidizing electrode?

Answer

(i) Electrode A - Anode
Electrode B - Cathode
(ii) Electrode A.

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Question 172 Marks

To carry out the so called "electrolysis of water", sulphuric acid is added to water. How does the addition of sulphuric acid produce a conducting solution?

Answer

When sulphuric acid is added to water it becomes good conductor as addition of sulphuric acid causes dissociation of water molecules into $H^+$ and $OH^-$ ions which are then responsible for conduction of electricity by pure water. The water thus obtained is called acidified water.

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Question 182 Marks

Classify the following substances under three headings:
(a) Strong electrolytes (b) weak electrolytes ( c) non- electrolytes
Acetic acid, ammonium chloride, ammonium hydroxide, carbon tetrachloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid.

Answer

(a) Strong electrolytes - dilute hydrochloric acid, dilute sulphuric acid, Ammonium chloride
(b) Weak electrolyte - Acetic acid, Ammonium hydroxide
(c) Non-electrolytes - Carbon tetrachloride

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Question 192 Marks

Write the equations for the reactions, which takes place at the electrodes during the electrolysis of lead bromide?

Answer

Equations for the reactions, which takes place at the electrodes : -
At Cathode :
$Pb^{+2} + 2e^- → Pb$
At anode :
$Br^-+ e^- → Br$
$Br+Br → Br_2.$

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Question 202 Marks

Copy and complete the following table which refers to two practical applications of electrolysis.

	Anode	Electrolyte	Cathode
Silver plating of a spoon		Solution of potassium argentocyanide
Purification of copper

Answer

	Anode	Electrolyte	Cathode
Silver plating of a spoon	Plate of pure clean silver	Solution of potassium argentocyanide	Cleaned article to be electroplated
Purification of copper	Impure copper	A solution of copper sulphate and dilute sulphuric acid	Thin strip of pure copper

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Question 212 Marks

If an electrolyte is described as a strong electrolytewhat does this mean?

Answer

If the electrolyte is described as strong electrolyteit means it completely dissociates into its constituting ions in aqueous solution.

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Question 222 Marks

What are the particles present in a compound which is a non- electrolyte?

Answer

Non- electrolyte are substances which do not conduct electricity in fused or aqueous state. They contain only molecules and do not ionize. For example: petrol, alcohol.

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Question 232 Marks

What is meant by the term electrolyte?

Answer

Electrolyte is a compound which either in aqueous solution or in molten state allows an electric current to pass through it and is accompanied by discharge of ions and finally into neutral atoms at the two electrodes.

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Question 242 Marks

Why is it necessary to add acid to water before proceeding with electrolysis of water?

Answer

Pure water does not conduct electricity because the degree of ionization is low. Thus to make it a good conductor of electricity acid is added to it which will increase the degree of ionization.

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Question 252 Marks

Define or explain the term: Electrolysis.

Answer

It is the process of decomposition of an electrolyte in the molten or aqueous state by discharge of ions at the electrodes on the passage of an electric current.

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Question 262 Marks

The following questions are about electroplating of copper wire with silver.
(a) What ions must be present in the electrolyte?
(b) Of what substance must the anode be made up of?
(c) What will the cathode be made up of?
(d) Write the equation for the reaction which takes place at the cathode.

Answer

(a) The ions of the silver must be present in the electrolyte.
(b) Anode should be made of pure clean silver.
(c) The cathode is made of copper wire.
(d) The equation for the reaction which takes place at the cathode is
$Ag^+ + e^- → Ag$

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Question 272 Marks

How is the passage of electricity through an electrolyte different from the passage of electricity through a copper wire?

Answer

The passage of electricity through an electrolyte occurs through ions furnished by the electrolyte where as the passage of electricity through a copper wire occurs through electrons.

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Question 282 Marks

List out the main applications of electrolysis.

Answer

The main application of electrolysis are :

Electroplating with metals
Electrorefining of metals
Extraction of metals

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Question 292 Marks

Explain, why during the electrolysis of copper sulphate using copper electrodes, the colour of solution does not fade?

Answer

During the electrolysis of copper sulphate using copper electrode, the number of copper ions remains same as that for evey copper ions discharged at the cathode, an ion of copper is formed at the anode which goes in the
solution. Thus the colour intensity does not change.

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Question 302 Marks

Give three applications of electrolysis.

Answer

Three applications of electrolysis are :

Electroplating with metals
Electrorefining of metals
Extraction of metals

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Question 312 Marks

Define the term : Cation and anion

Answer

Cation and anion :

Cation : Positively charged ions are called cations. For example : $Na^+.$
Anion : Negatively charged ions are called anions.
For example : $Cl^-.$

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Question 322 Marks

Define the term : Electrolysis

Answer

Electrolysis :
It is the process of decomposition of the electrolyte in the molten or aqueous state by discharge of ions at the elctrodes on passage of an electric current.

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Chemistry [2 Mark Question Answer]

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