Electrolysis

(a) X ⟶ X²⁺ + 2e^-

Y + 3e^- ⟶ Y^3-

(b) 3X + Y₂ ⟶ X₃Y₂

(c) If the compound formed between X and Y is melted and an electric current passed through the molten compound, the element X will be obtained at the cathode and Y at the anode of the electrolytic cell.

(a) Labeled diagram showing electroplating of Iron with Copper is shown below:

(b) CuSO₄ is preferred as electrolyte must be a solution of a salt of metal to be electroplated.

(c) The copper anode continuously dissolves as ions in solution and is replaced periodically. The electrolyte dissociates into Cu²⁺ ions which migrate towards the iron object taken as the cathode. Here, the Cu²⁺ ions gain electrons and become atoms of copper which deposit on the iron object as a firm coating. Thus, the iron object gets electroplated with copper.

(a) It is a Complex Salt.

(b) Migration of Ag¹⁺ ions from above complex salt soln. is slow compared to that from silver nitrate. Hence, an even deposition of silver metal is obtained on the article. Therefore, the electrolyte sodium argentocyanide soln. is preferred over silver nitrate solution.

(c) A low current for a longer time should be used to ensure that the deposit is smooth, firm and long lasting.

(d) Ag¹⁺ + 1e^- ⟶ Ag [deposited]

(e) Ag - 1e^- ⟶ Ag¹⁺ [Anode diminishes in mass]

(a) At cathode — Cu²⁺ ions and H¹⁺ ions migrate to the cathode. Cu²⁺ ions are below H¹⁺ ions in the activity series, thus Cu²⁺ ions are discharged in preference to H¹⁺, to form neutral copper atoms. Thus, copper atoms deposit themselves on the cathode.

At anode — SO₄^2- and OH^1- ions migrate to the anode but OH^1- ions are discharged since they are lower in the electrochemical series. The neutral (OH) radicals reunite to form water and oxygen.

(b) The blue colour of CuSO₄ solution fades since the blue Cu²⁺ ions which are discharged at the cathode are not replaced at the anode.

(c) Cathode : Cu²⁺ + 2e^- ⟶ Cu

Anode: 4OH^1- - 4e^- ⟶ 4OH

2OH + 2OH ⟶ 2H₂O + O₂

(i) Ag - e^- ⟶ Ag⁺

(ii) Cu - 2e^- ⟶ Cu²⁺

(iii) Cl^- - e^- ⟶ Cl
      Cl + Cl ⟶ Cl₂

(a) In electroplating, the cathode is the electrode where reduction (gain of electrons) occurs. The iron cup is placed at the cathode because the metal ions from the electrolyte will be reduced and deposit onto the iron cup. This process coats the iron cup with a layer of metal, achieving the plating effect.

(b) Ni²⁺ must be present in the electrolyte.

(c) A low current for a longer time should be used as longer time and low current initiates a thicker, uniform deposit.

(d) Ni²⁺ + 2e^- → Ni

(e) The Nickel plate is gradually dissolved as ions in solution.

(a) The electrode connected to the positive terminal of the battery (i.e., electrode on the left) is the oxidizing electrode as anions donate excess electrons to the anode and are oxidized to neutral atoms.

(b) Cu - 2e^- ⟶ Cu²⁺

(c) Copper anode shows a loss in mass. The blue colour of aq. copper sulphate soln. remains unchanged.

Lead is deposited at the cathode

Reason — The positive lead ions ( Pb²⁺) migrate towards the cathode when the current is turned on. They take 2 electrons each and become neutral lead atoms.

Reaction at cathode :

Pb²⁺ + 2e^- ⟶ Pb

Silvery gray metal lead is formed on the cathode.

Acetic acid [CH₃COOH]

Reason — Acetic acid is a weak electrolyte and particles in a weak electrolyte are ions and unionized molecules.

Lead (II) bromide

Reason — During electrolysis of Lead [II] bromide, Br^-1 ions are discharged at the anode. Reddish brown fumes are due to bromine vapours.

Aqueous acetic acid.

Reason — Aqueous acetic acid is a weak electrolyte because they partially dissociate and allow small amount of electricity to flow through them.

Cu²⁺

Reason — Ion's place in the electrochemical (reactivity) series determines how easily they discharge during electrolysis. Ions in a lower position discharge more easily and are less reactive.

Ag

Reason — During silver plating using potassium argento-cyanide as an electrolyte, the anode should be block of pure clean silver.
The anode dissolves, supplying Ag⁺ ions to the electrolyte. These Ag⁺ ions then get reduced at the cathode (the article to be plated) and deposited as metallic silver.

Liquid carbon tetrachloride

Reason — Carbon tetrachloride (CCl₄) is a liquid that does not conduct electricity because it is a non-polar covalent compound. In the case of CCl₄, carbon atom shares electrons with four chlorine atoms. The electrons are shared equally between the atoms, and the molecule has no permanent dipole moment, meaning there is no separation of charge. Therefore, there are no ions present in the compound, and no free electrons to carry an electrical current.

a silver grey deposit at cathode and reddish brown fumes at anode.

Reason — Silver grey colour is due to lead metal deposited at cathode and reddish brown fumes at anode is due to bromine vapours.

Sodium argentocyanide solution

Reason — Sodium argentocyanide solution is used as electrolyte during silver plating because it allows slow and smooth plating, which is essential for a uniform and bright finish. If silver nitrate solution is used directly instead of double cyanide of sodium and silver, the deposition of silver will be very fast and hence not very smooth and uniform .

Pt

Reason — Platinum is used as a inert electrolyte, as they will not take part in the electrolytic reaction.

OH^-

Reason — The SO₄^2- and OH^- ions both migrate to the anode. The OH^- ions, being lower in electrochemical series as compared to SO₄^2- ions, discharge to form neutral (OH) radical. The neutral (OH) radicals reunite to form water and oxygen.

4OH^- - 4e^- ⟶ 4OH

H⁺

Reason — Na⁺ and H⁺ (H₃O⁺) migrate to cathode. But despite high concentration of Na⁺, H⁺ gains electron more easily than Na⁺, (sodium is above hydrogen in electro-chemical series). It is the H⁺ ions that accept electrons.

H⁺ + e^- ⟶ H

cations gain electrons from cathode

Reason — The reaction at cathode involves reduction of cations as they gain electrons to become neutral atoms. Hence, cathode is a reducing electrode and cations gain electrons from cathode.

Electricity is conducted in an acidic solution by ions.

Reason — Acids when dissolved in water get ionized into their respective ions.These ions are mobile and allow the solution to carry electric current.
For example :
HCl in water conduct electricity through ions like H⁺ and Cl⁻.

However, in aqueous solutions (like saltwater or acids) or in molten electrolytes (like molten NaCl), electricity is conducted by ions, not electrons. In metals, electricity is conducted by free electrons, not ions. Hence other options cannot be right.

Fe²⁺ - e^- ⟶ Fe³⁺

Reason — Oxidation is defined as a process in which an atom or an ion loses electron(s).

In the reaction

Fe²⁺ - e^- ⟶ Fe³⁺

Fe²⁺ loses one electron and forms Fe³⁺. So, this is an oxidation reaction.

Only P

Reason — Metallic ions, which are positively charged cations, migrate to the cathode during electrolysis. At the cathode, they gain electrons and are discharged as neutral metal atoms. Hence, during electrolysis, reduction of metallic ions occurs at cathode.

Both A and R are true but R is not the correct explanation of A.

Explanation — Electrolysis is a process that demonstrates the conversion of electrical energy into chemical energy. Hence, assertion (A) is true.
Metals and graphite are conductors, while salts like NaCl and KCl (in molten or aqueous form) are electrolytes. Hence, Reason (R) is true.
However, knowing which substances are conductors or electrolytes does not establish the relationship between electrical and chemical energy. Hence, both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

Both A and R are true and R is the correct explanation of A.

Explanation — Benzene is a non-electrolyte that does not have ions even in solution. They contain only molecule. Hence both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).

Both A and R are true but R is not the correct explanation of A.

Explanation — Metal and alloys (mixtures of metals) conduct electricity using free electrons in their outer shells that move easily in solid state. Hence assertion (A) is true. Non-metals generally do not have free electrons, which is why they are poor conductors of electricity. Hence the reason (R) is true.

However,it does not precisely explain why metals and alloys conduct electricity , the reason (R) only explains why non-metals are poor conductor of electricity. Hence reason (R) is not correct explanation for assertion (A).

A is false but R is true.

Explanation — Electrolytes which allow small amounts of electricity to flow through them are called weak electrolytes. These are poor conductors of electricity. Hence the assertion (A) is false.
Substances which are composed of only molecules are non electrolytes, they do not allow any current to flow through them. For example, Benzene, glucose.
Hence the reason (R) is true.

Both A and R are true and R is the correct explanation of A.

Explanation — NaCl is an electrolyte because it conducts electricity when dissolved in water or in molten form, due to the presence of free-moving ions. Therefore, both the assertion (A) and the reason (R) are true, and the reason correctly explains why NaCl is an electrolyte.

Both A and R are true but R is not the correct explanation of A.

Explanation — Electrolytes include acids (like HCl), bases (like NaOH), and salts (like NaCl). Hence, assertion (A) is true.
Electrolytes conduct electricity in aqueous or molten states because they produce ions. Hence, Reason (R) is true.
The reason correctly describes what an electrolyte does, but it doesn’t directly explain why acids, bases, and salts are classified as electrolytes. Hence, both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

A is true but R is false.

Explanation — The reaction at anode involves oxidation of anions as they lose electrons to become neutral. Hence the assertion (A) is true.
Electrons are donated or lost at the anode. However, gain of electrons takes place at cathode, where cations are reduced. Hence the reason (R) is false.

Both A and R are true but R is not the correct explanation of A.

Explanation — Polar covalent compounds are converted into ions in water , and these ions conduct electricity. Hence assertion (A) is true.
For example : water.

Electrovalent compounds when melted or dissolved in water, electrostatic force of attraction is broken and they dissociate into ions and conduct electricity.Hence the reason (R) is true.

Since reason (R) doesn't explain the ionisation of polar covalent compound it is not correct explaination of assertion (A).

A is true but R is false.

Explanation — The block of pure silver is used as anode because it is active electrode, as it slowly dissolves in the solution, Ag⁺ ions are produced for the plating process. Hence the assertion (A) is true.

Silver ions are deposited on to the article that acts as cathode. Hence reason (R) is false.

The blue colour of CuSO₄ solution is due to the Cu²⁺ ions. During it's electrolysis using Pt electrodes, at the cathode Cu²⁺ ions are discharged as neutral copper atoms by accepting electrons. These are not replaced by Cu²⁺ ions from the anode because at the anode, OH^- ions are discharged. As Cu²⁺ ions decrease, the blue colour of CuSO₄ solution fades and it becomes almost colourless as soon as Cu²⁺ ions are finished.

Solid lead bromide is a non-electrolyte since it's ions are not free but held together by strong electrostatic forces of attraction. These ions become free when lead bromide is in fused or molten state, hence it undergoes electrolytic dissociation in the fused or molten state.

As aluminium is higher in the electrochemical series, hence it has a strong affinity for oxygen and its oxides are highly stable. It is not possible to reduce the oxides by common reducing agents like carbon monoxide and hydrogen. Hence, electrolytic reduction is used.

In the electrolysis of acidified water:

At anode OH^- loses one electron and becomes neutral OH.

OH^- ⟶ OH + e^-

The combination of OH forms water with the liberation of oxygen.

2OH + 2OH ⟶ 2H₂O + O₂

Since, 4 OH neutral particles are involved in the equation so 4 electrons are lost in order to get 4 OH neutral particles.

4OH^- ⟶ 4OH + 4e^-

Thus, the formation of 1 molecule of oxygen at the anode releases 4 electrons and to ensure that there is no build-up of electrons in any part of the circuit, the reaction of the cathode must take up 4 electrons,

i.e., 4H⁺ + 4e^- ⟶ 2H₂

This shows that the number of molecules of hydrogen is twice that of oxygen.

According to Avogadro's Law, molecules can be substituted by volumes. Hence, electrolysis of water gives 2 volumes of H₂ and 1 volume of O₂.

Dilute sulphuric acid is non-volatile while dilute nitric acid is a volatile acid. It may decompose and nitrate radical (NO₃^1-) may tend to interfere with the electrolytic reaction. Hence, in the electrolysis of acidified water, dilute sulphuric acid is preferred to dilute nitric acid.

NH₃ is polar covalent in nature, i.e., shows charge distribution in its molecules such that the 3 hydrogen atoms have a slight positive charge and Nitrogen atom has a slight negative charge.

The nitrogen atom in ammonia has a lone pair of electrons. In aqueous solution, the ammonia molecule combines with a hydrogen atom H⁺ by sharing the lone pair of electrons of nitrogen atom to form ammonium ion (NH₄⁺). Thus, in water, ammonium hydroxide (NH₄OH) dissociates into NH₄⁺ (ammonium ion) and OH^- (hydroxide ion) as follows:

NH₄OH ⟶ NH₄⁺ + OH^-

Due to this ionization, aqueous solution of ammonia (NH₄OH) behaves as a weak electrolyte.

Direct current flows in one direction, allowing the electrodes to maintain fixed polarity. One electrode is always the anode (+) (where oxidation occurs), and the other is always the cathode (–) (where reduction occurs).

Carbon tetrachloride (CCl₄) is a liquid that does not conduct electricity because it is a non-polar covalent compound. In the case of CCl₄, carbon atom shares electrons with four chlorine atoms. The electrons are shared equally between the atoms, and the molecule has no permanent dipole moment, meaning there is no separation of charge. Therefore, there are no ions present in the compound, and no free electrons to carry an electrical current.

Potassium is not extracted from it's aqueous salt solution by electrolysis as aqueous solution will contain H⁺ ion along with metal ion. On the passage of electric current the H⁺ ion gets discharged in preference to metal. Thus, the product formed at cathode is hydrogen gas and not the metal.

Water in pure state consists almost entirely of molecules. It is a polar covalent compound and can form ions when traces of dilute sulphuric acid is added. As dilute sulphuric acid catalyses this ionisation, hence this electrolysis of acidified water is considered as an example of catalysis.

As graphite is unaffected by the reactive bromine vapours released at the anode hence, a graphite anode is preferred to other inert electrodes like platinum during the electrolysis of molten lead bromide.

Electrolysis of molten lead bromide involves oxidation and reduction reactions and hence is a redox reaction.

Reduction reaction at cathode:
Pb²⁺ + 2e^- ⟶ Pb

Oxidation reaction at the anode:
Br^1- - 1e^- ⟶ Br
Br + Br ⟶ Br₂

(a) The ions Na⁺ and Cl^- are not free but held together by strong electrostatic force of attraction. In fused or molten state the ions break free and move. Hence, NaCl will conduct electricity only in fused state or aq. soln. state.

(b) Migration of Ag¹⁺ ions from sodium argento-cyanide solution is slow compared to that from silver nitrate. Hence, an even deposition of metal silver is obtained on the article. Therefore, the electrolyte sodium argento-cyanide solution is preferred over silver nitrate solution.

(c) Copper does not undergo chemical decomposition due to flow of electric current through it. Hence, copper is a good conductor of electricity but it is a non-electrolyte.

1. Electroplating of metals
2. Electrorefining of metals

Cu²⁺ (Copper ions will get discharged at cathode) as between magnesium, iron and copper, copper is the lowest in electrochemical series.

Reaction at Cathode:
Cu²⁺ + 2e^- ⟶ Cu

(i)
A. The electrolyte — Aq. soln. of nickel sulphate
B. The cathode — Cleaned article to be electroplated
C. The anode — Plate or block of nickel metal

(ii) the reaction of the electrolysis at:

A. At Cathode: Ni²⁺ + 2e^- ⟶ Ni

B. At Anode : Ni - 2e^- ⟶ Ni²⁺

As NaCl is a strong electrolyte (i.e., cell A), therefore it allows large amount of electricity to flow through it. Hence, the bulb glows brightly.

Acetic acid is a weak electrolyte (i.e., cell B) and it allows a small amount of electricity to flow through them hence, the bulb glows dimly.

Sugar soln. is a non-electrolyte (i.e., cell C), therefore it does not conduct electricity and do not undergo chemical decomposition due to the flow of current through it. Hence, the bulb does not glow

When electricity is passed through molten lead bromide solution, dark reddish brown fumes of bromine evolve at the anode.

Br^- - e^- ⟶ Br

Br + Br ⟶ Br₂

Copper, a brownish pink metal is deposited at the cathode when acidified aqueous copper sulphate solution is electrolysed with copper electrodes.

Copper anode shows a loss in mass.

Anode is the oxidizing electrode.

Reason — The anions donate the excess electrons to the anode and are oxidized to neutral atoms. Hence, the anode is the oxidizing electrode by which the electrons leave the electrolyte.

(a) Reaction at cathode : M⁺ + e^- ⟶ M

(b) Product at anode : Oxygen

Cations are formed by loss of electrons and anions are formed by gain of electrons.

(i) Strong electrolyte — Sodium (Na⁺) ions and hydroxide (OH^-) ions.

(ii) Weak electrolyte — Ions (H⁺, HCO₃, CO₃^2- ) and molecules (H₂CO₃)

(iii) Non-electrolyte — Molecules of sugar soln.

(a) Non-electrolyte contains molecules.

(b) Molecules of HX and H⁺ and X^- ions.

(c) The electrolyte must contain ions of the metal which is to be electroplated on the article.

AgNO₃ solution will turn blue.

Reason — Copper is unable to displace potassium, calcium and zinc from their nitrate solution as they are higher than copper in the metal activity series.

But silver being lower than copper in metal activity series gets displaced by copper and blue coloured copper nitrate is formed.

2AgNO₃ + Cu ⟶ Cu(NO₃)₂ + 2Ag

Cu ⟶ Cu²⁺ + 2e^-

This reaction takes place at anode.

This is an example of oxidation.

(i) Nickel ion moves towards the cathode.

(ii) Product at anode - Nil [Nickel anode loses electrons to give Ni²⁺ ions in solution]

Hydrogen chloride gas

Electroplating

(a) Powdered sodium chloride (common salt) does not conduct an electric current, but it does so when in aqueous state or when in molten state .

(b) Molten lead bromide conducts electricity. It is called an electrolyte. It is composed of lead ions and bromide ions. The lead ions are positively charged and are called cations. The bromide ions are negatively charged and are called anions.

(c) Substances which conduct electricity in the solid state are generally metals .

(d) The electron releasing tendency of zinc is more than that of copper.

(e) A solution of HCl gas in water conducts electricity because it ionizes , but a solution of HCl gas in toluene does not conduct an electric current because it does not ionize.

(f) Pure water consists entirely of molecules

(g) We can expect that pure water will not normally conduct electricity.

(h) Electrolysis is the passage of electricity through a liquid or a solution accompanied by a chemical change.

(a) Electrolysis — It is the process of decomposition of a chemical compound in aqueous solution or in molten state accompanied by a chemical change using direct electric current.

(b) Non-electrolyte — It is a compound which neither in solution nor in the molten state allows an electric current to pass through it.

(c) Cation — Ions carrying positive charge are called cations.
     Anion — Ions carrying negative charge are called anions.

(d) Weak electrolyte — Electrolytes which allow small amount of electricity to flow through them and are partially dissociated in aqueous solution are called weak electrolytes.

(a) Lead acetate

(b) Ammonium hydroxide

(c) Inert electrode: Graphite and Active electrode: Copper

(d) H⁺

(e) Cathode

(f) Graphite

During electrolysis, the reaction at the cathode involves reduction of cations as they gain electrons to become neutral atoms while that at anode involves oxidation of anions as they lose electrons to become neutral. As redox reactions are reactions where oxidation and reduction takes place simultaneously. Hence, electrolysis is a redox process.

Example : Dissociation of sodium chloride during electrolysis.

NaCl ⇌ Na⁺ + Cl^-

At cathode : Na⁺ + e^- ⟶ Na (reduction)

At anode : Cl^- - e^- ⟶ Cl (oxidation)

Cl + Cl ⟶ Cl₂

Overall reaction: 2NaCl ⟶ 2Na + Cl₂

(a) Strong electrolytes — dilute hydrochloric acid, dilute sulphuric acid, sodium acetate, ammonium chloride

(b) Weak electrolytes — acetic acid, ammonium hydroxide

(c) Non-electrolytes — carbon tetrachloride

(a) Copper does not undergo chemical decomposition due to flow of electric current through it. Hence, copper is a good conductor of electricity but it is a non-electrolyte.

(b) In solid sodium chloride, ions Na⁺ and Cl^- are not free to move due to the strong electrostatic forces. Hence, solid sodium chloride does not allow electricity to pass through it.

(i) Molten ionic compound — B (Strong electrolyte)

(ii) Carbon tetrachloride — A (Non-Electrolyte)

(iii) An aluminium wire — D (Metallic conductor)

(iv) A solution containing solvent molecules, solute molecules and ions formed by the dissociation of solute molecules — C (Weak electrolyte)

(v) A sugar solution with sugar molecules and water molecules — A (Non-Electrolyte)

Sodium hydroxide

NaOH ⇌ Na⁺ + OH^-

(a) Distilled water, alcohol

(b) NaOH, KOH

(c) Carbonic acid , acetic acid

(a) OH^-, Lower the position of the anion in the series, more easily it gets discharged at anode.

(b) Ag⁺, Elements lower in the series gets discharged more easily at the cathode during electrolysis because their cations can easily gain electrons.

(a) Zn has more tendency to release electrons, thus Zn occurs more readily as ion while Cu as metal.

(b) As copper lies above silver in electrochemical series, hence, Cu is more reactive than silver and it displaces Ag from silver nitrate.

Cu + AgNO₃ ⟶ Cu(NO₃)₂ + 2Ag

(c) Cu is more reactive than Ag hence, Cu lies above Ag in the electrochemical series.

(a) By the method of electrolysis, metal like Cu can be changed into it's ions.

Using —

electrolyte : A solution of copper sulphate and dil. sulphuric acid

Cathode : Thin strip of pure copper

Anode: Impure copper

When the current is passed through the electrolyte, the copper block loses electrons and passes into solution as soluble copper ions.

Cu - 2e^- ⟶ Cu²⁺

(b) By the same process as above, when current is passed through the electrolyte, the copper ions of the copper sulphate solution are attracted to the cathode where they gain electrons and gets deposited on the copper strip.

Cu²⁺ + 2e^- ⟶ Cu

When caustic soda is dissolved in water or fused, the forces of attraction between their ions are broken and the ions then move about and conduct electricity.

(a) SO₄^2- and OH^-

(b) SO₄^2- and OH^- both migrate to the anode. OH^- being lower in the electrochemical series is discharged preferentially.

OH^- loses one electron to the anode and becomes neutral OH.

OH^- ⟶ OH + e^-

The combination of OH forms water with the liberation of oxygen, which is given off at the anode.

OH + OH ⟶ H₂O + O

O + O ⟶ O₂

(c) The product formed at cathode is hydrogen.

The reaction is : H⁺ gains an electron and become neutral hydrogen atom.

H⁺ + e^- ⟶ H

Hydrogen atoms combine to form molecule and this comes out as hydrogen gas.

H + H ⟶ H₂

(d) No change in colour is observed.

(e) Water in pure state consists almost entirely of molecules. It is a polar covalent compound and can form ions when traces of dilute sulphuric acid is added. As dilute sulphuric acid catalyses this ionisation, hence this electrolysis of acidified water is considered as an example of catalysis.

(a) A = Platinum anode, B = Platinum or copper cathode

(b) A = Platinum anode as oxidation of non-metal ions always takes place at the anode.

Water in pure state consists almost entirely of molecules. Hence it is a non-electrolyte that will not conduct electricity.
Water is a polar covalent compound. It can be electrolytically decomposed by addition of traces of dil. H₂SO₄ which dissociates as: H⁺¹ and SO₄^2- and help in dissociating water into H⁺¹ and OH^- ions. Thus, dilute sulphuric acid catalyses the ionisation of water to produce a conducting solution.

The electroplating of an article with nickel requires an (i) electrolyte which must be a solution containing (ii) nickle ions. The article to be plated is placed as the (iii) cathode of the cell in which the plating is carried out. The (iv) anode of the cell is made from pure nickel. The ions that are attracted to the negative electrode and discharged are called (v) cations

(b) When a molten ionic compound is electrolysed, the metal is always formed at cathode and the non-metal is formed at anode

(c) Electrolysis of acidulated water is an example of redox reaction

A solution of cane sugar does not conduct electricity because it is composed of molecules that do not dissociate into ions when dissolved in water. In contrast, a solution of sodium chloride does conduct electricity because sodium chloride is an ionic compound consisting of sodium (Na⁺) and chloride ions (Cl^-). When dissolved in water, the sodium ions (Na⁺) and chloride ions (Cl^-) become free to move independently and can carry an electric current.

HCl is polar covalent in nature, i.e., shows charge distribution in its molecules such that the hydrogen atom has a slight positive charge and the chlorine atom has a slight negative charge.

H^δ+ — Cl^δ-

When hydrogen chloride is added to water [a polar covalent solvent], the slightly negative charged oxygen atom of water exerts an electrostatic pull on the slightly positively charged hydrogen ions present in the molecule of HCl.

Thus, H⁺ ions combine with water to form hydronium ions [H₃O]⁺.

The presence of hydronium and chloride ions makes hydrochloric acid a good conductor of electricity.

Na⁺ and H⁺ migrate to cathode, but as H⁺ has lower position in electrochemical series than Na⁺, so hydrogen ion is reduced at the cathode and not the sodium ion.

H⁺ + e^- ⟶ H

In the electrochemical series, copper is placed below hydrogen. Thus, copper ions discharge at the cathode over H⁺ ions. That's why copper is deposited at the cathode but no hydrogen gas evolves there.

In the electrochemical series, hydrogen is placed much below sodium, hence, hydrogen is discharged at the cathode in preference to sodium.

Zinc is more reactive than hydrogen and is placed above hydrogen in the reactivity series, so it displaces hydrogen from acids, but copper is less reactive than hydrogen and is placed below hydrogen in the reactivity series, so it does not liberate hydrogen from acids.