Explore topic-wise InterviewSolutions in .

Water is a non-conductor of electricity and consists entirely of molecules. It can be electrolytically decomposed by addition of traces of dilute sulphuric acid which dissociate as H⁺ and SO₄^2- ions and help in dissociating water into H⁺ and OH^-, water being a polar solvent.

(i) Articles are electroplated for the following reasons: 

a) To prevent it from corrosion.

(b) To improve the appearance of the metal articles.

(ii) To get a uniform and smooth coating of superior metal, a small current should be used -for a longer time.

(iii) The article to be electroplated is always placed at cathode because the metal is always deposited at cathode.

(iv) Direct current is used to get smooth coating and the phase of the current is same at all instance of time. 

Silver nitrate solution is taken in a beaker. Silver wire and a spoon, which is to be plated with silver, are dipped in the solution. Silver wire is connected with the positive terminal of the battery which acts as anode and spoon is connected with the negative terminal of the battery which acts as cathode. When electric current is passed through silver nitrate solution, electrolysis takes place and silver is deposited as a fine thin film at the surface of spoon. The spoon is coated with silver and looks as a silver spoon. 

The blue colour of electrolyte is due to the presence of copper ions in it. As the electrolysis is . carried out, the copper ions discharge at the cathode.

Cu²⁺ + 2e^– ⟶ Cu

However, no copper ions enters in the electrolyte from anode. Thus concentration of copper ions goes on decreasing. This result in fading of blue colour. When copper ions completely finish the electrolyte becomes colourless.

Reaction of cathode:

H⁺ + e^– ⟶ H

H + H ⟶ H₂

Reaction of anode :

OH^– – 1e^– ⟶ OH

4OH ⟶ 2H₂O + O₂(g)

1. Electrolysis of molten PbBr₂ using inert electrodes.

 PbBr₂ (l)  ⇋  Pb²⁺ (l) + Br^- (l)

At cathode:

Pb²⁺ (l) + 2e^– → Pb (s)

At anode:

2Br^– (l) – 2e^– → 2Br

Br + Br → Br₂ (g)

2. Electrolysis of acidified water using Pt electrodes.

At cathode :

4H₂O (l)  ⇋ 4H⁺(aq) + 4OH^- (aq)

4H⁺(aq)  + 4e^– → 4H

2H + 2H^–→ 2H₂

At anode :

4OH⁺ (aq) – 4e^– → 4OH

4OH →  2H₂O (l) + O₂ (g)

Pure copper will deposit at cathode. 

 (i) B, (ii) A, (iii) D, (iv) C, (v) A.

Addition of sulphuric acid causes dissociation of water molecules into [H⁺] and [OH^–] ions. 

Flow of electricity through nickel wire

1. It is due to the flow of electrons.

2. It is a physical change.

3. It can take place in solid state.

4. Electrical conductivity is more.

low of electricity through nickel sulphate solution

1. It is due to the flow of ions.

2. It is a chemical change.

3. It cannot take place in solid state.

4. Electrical conductivity is less. 

1. Electrolysis of aq. CuSO₄ using copper anode: As copper can easily lose electron, copper from anode will dissolve as Cu²⁺ ions. 

Cu (s) – 2e^–→ Cu²⁺ (aq)

2. Electrolysis of aq. CuSO₄ using inert platinum anode: Due to very low tendency of platinum to lose electron platinum anode does not take part in electrolytic reaction. Further tendency of SO₄^2- to lose electron is much less than that of OH^– (from feebly ionised water). Thus OH^– ions get oxidised in preference to SO₄^2- ions to give O₂

4OH – 4e → 4OH

4OH→ 2H₂O + O₂↑

Differences between electrical conductivity of copper sulphate solution and copper metal:

(a) The ratio is 2 : 1

(b) H⁺ + e^– ⟶ H;

2H + 2H ⟶ 2H₂

 Molecules are present in a non-electrolyte.

(i) Mass of Cathode increases where as that of anode decreases due to deposition of pure copper on cathode.

(ii) The blue colour of copper sulphate is due to the presence of cupric ions (Cu⁺⁺ ). Cu⁺⁺ ions are discharged at the cathode and deposited as Pinkish copper metal, but OH^– ions are discharged at anode. The electrolyte consists of hydrogen and sulphate ions which associate to form colourless sulphuric acid. 

(iii) The electrolysis of copper sulphate solution is used in the purification of copper using pure copper plate as cathode and impure copper plate as anode.

Molten lead bromide conducts electricity. 

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

Hydrochloric acid dissociates into ions in aqueous solution as follows:

HCl  ⇌  H⁺ + Cl^– 

When a current is passed through in aqueous solution of HCl, the ions move towards their respective electrodes. Thus, the hydrochloric acid is a conductor of electricity.

The conductivity of metals is due to movement of electrons.

Lead ions and bromide ions are present in pure lead bromide in molten state. 

During electrolysis of aqueous copper sulphate using copper electrodes, the two anions OH^–  and SO₄^2- migrate to the anode, but none of them get discharged because the copper of the anode dissolves in the solution producing copper ions and electrons. Hence, OH^– and SO₄^2-  ions remain as spectator ions.

Lead bromide should be in molten state, if it is to conduct electricity.

No, wax does not conduct electricity because wax, being a covalent compound, does not have positively or negatively charged ions which could not be weakened by heating or in aqueous solution. Therefore due to absence of free ions, wax does not conduct electricity. 

In the aqueous state, the slightly negatively charged oxygen atoms of the polar water molecule exerts a pull on the positively charged sodium ions. A similar pull is exerted by the slightly charged hydrogen atoms of the water on the negatively charged chloride ions. Thus the ions become free in solution. These free ions conduct electricity.

In the molten state, the high temperatures required to melt the solid weakens the bond between the particles and the ions are set free.

(a) Two anions are SO 2⁻4 and OH^-.

(b) OH^- is discharged at anode and the main product of the discharge of OH^- is O₂

Reaction is :

OH^- ⟶ OH + e^-

4OH ⟶ 2H₂O + O₂

(c) The product formed at cathode is hydrogen. The reaction is :

H⁺ + e^- ⟶ H

H + H ⟶ H₂

(d) No change in colour is observed.

(e) Dilute sulphuric acid catalyse the dissociation of water molecules into ions, hence electrolysis of acidified water is considered as an example of catalysis.

1. Cathode : Reddish brown deposition of copper occurs at cathode.

Anode : Colourless gas is evolved at anode.

2. On prolonged electrolysis, the blue electrolyte turns colourless. .

3. Cathode :  Cu²⁺   +  2e^– → Cu

   Anode :    OH^– — Ie^– → OH

                    4OH → 2H₂O + O₂ ↑ 

The sugar cane solution is a covalent compound. When it is dissolved in water, does not dissociate to give free ions which could migrate to cathode or anode. Hence, sugar solution is bad conductor of electricity. The sodium chloride solution mainly consists of free sodium and chloride ions which could migrate to positively charged electrodes. Hence, solution of sodium chloride is good conductor of electricity. 

(a) Cane sugar is a compound which does not have ions even in solution and contains only molecules. Hence, it does not conduct electricity. On the other hand, sodium chloride solution contains free mobile ions and allows electric current to pass through it. This makes it a good conductor of electricity.

(b) Hydrochloric acid is a strong electrolyte and dissociates completely in aqueous solution. The solution contains free mobile ions which allow electric current to pass through it. Hence, hydrochloric acid is a good conductor of electricity.

(c) Hydrogen is placed lower in the electrochemical series and sodium is placed at a higher position. This is because H⁺ ions are discharged more easily at the cathode than Na⁺ during electrolysis and gains electrons more easily.

Therefore, H⁺ ion is reduced at the cathode and not Na⁺ ion.

(a) Because Copper is an electronic conductor as it is a metal.

(b) In solid sodium chloride, Na+ and Cl - ions are not free due to strong electrostatic forces of attraction among them. The ions, therefore are unable to move to any large extent when electric field is affected. Hence no current.

Copper metal – is a good conductor of electricity – but is a non-electrolyte, sinceIt does not undergo chemical decomposition due to flow of electric current through it

(D) Aqueous acetic acid.

1. Oxygen

2. Silver ions

1. During the electrolysis of molten lead bromide, a graphite anode is preferred because graphite remains unaffected by the reactive bromine vapours which are released at the anode.

2. Sulphuric acid is a strong acid compared to acetic acid. A strong acid has more ions than a weak one, and so, its solution will be a better electrical conductor than a weak acid. So, electrical conductivity of acetic acid is less in comparison of electric conductivity of sulphuric acid.

3. In the electrolysis of molten lead bromide, the following reactions take place:

At the cathode :  Pb²⁺ (l) + 2e^– → Pb(l)

At the anode : 2Br (l) → Br₂ (g) + 2e^–

Lead (II) ions (Pb²⁺ ) are attracted to the negative electrode, and the Pb²⁺ ions are forced to accept two electrons. Pb²⁺ ions are reduced. Bromide ions (Br^– ) are attracted to the positive electrode and the bromide ions are forced to give away their extra electron to form bromine atoms. Thus, bromide ions are oxidised. So, electrolysis of molten lead bromide is a redox reaction

The amount of acid in the water does not change. Furthermore, it does not take part in electrochemical reaction, but makes the water a good conductor of electricity.

(i) Copper ions (Cu²⁺ ) and hydrogen ions H⁺ migrate to cathode.

(ii) Chloride ions (Cl^– ) and hydroxyl ions OH^– migrate to anode.

(iii) Copper ions (Cu²⁺ ) are likely to discharge at cathode, because their position is lower than hydrogen ions H+ in electrochemical series.

(iv) Cu²⁺ + 2e^– ⟶ Cu

(v) Hydroxyl ions (OH^– ) are likely to discharge at anode, because their position is lower than chloride ion (Cl^– ) in electrochemical series.

(vi) 4OH^– – 4e^– ⟶ 2H₂O + O₂ (g)

(vii) The electrolyte gets decolourised. It is because, the blue colour of electrolyte is due to the presence of Cu²⁺ ions. As Cu²⁺ ions discharge at cathode, therefore their concentration in electrolyte decreases. Thus, gradually blue colour fades away.

(viii) In such a situation the copper atoms on copper anode ionise and enter into electrolyte. Thus, size of copper anode gradually decreases. This is not possible in case of graphite anode.

(ix) Hydrogen gas is liberated at cathode.

During metallic conduction, the chemical properties of copper are intact as it does not undergo chemical decomposition. Since, the flow of electricity only produces heat and energy and no new products are formed copper metal is thus a good conductor of electricity but is a non electrolyte.

1. NaCl will conduct electricity only molten state or when dissolved in water. This is because the Na⁺ and Cl^– ions present in solid NaCl are too big to move under the influence of applied electric field.

2. HCI gas is a polar covalent compound when dissolved in water, it will ionise to give H⁺ and CP ions. Under the influence of applied electric field these ions can easily move in an aqueous solution and thus conduct electricity. Thus HCI (g) when dissolved in water conducts electricity.

3.  NH₃ (g) will dissolved in water to give NH₄OH.

NH₃ (g) + H₂O (l) → NH₄OH (aq)

NH₄OH(aq)  ⇋  NH⁺_4 (aq) + OH^-(aq)

NH₄OH will ionise to give NH₄⁺ and OH^– ions. Under the influence of applied electric field these ions can migrate in an aqueous solution and hence conduct electricity. Thus NH₃ (g) when dissolved in water conduct electricity.

Acids, bases and salts are classified as electrolytes because these compounds dissociate into ions, conduct electricity and undergo chemical decomposition at the same time. 

Sea water is a strong electrolyte because sodium chloride dissolved in it dissociates completely into free mobile ions.

Na⁺Cl^-  ⇌  Na⁺ + Cl^– 

Strong electrolytes – Compound which in the fused or in the aqueous solution state are almost completely dissociated and are good conductors of electricity are called.

Weak Electrolytes – Compound which in the fused or in the aqueous solution state are feebly or partially dissociated and are poor conductors of electricity are called – weak electrolytes. 

Strong electrolytes —Ammonium chloride, dilute hydrochloric acid, dilute sulphuric acid. 

Weak electrolytes — Ammonium hydroxide, acetic acid, sodium acetates.

Non-electrolyte — Carbon tetra chloride

Strong electrolytes :

1. The compounds which in their aqueous solution or in fused state are almost completely ionised are called strong electrolytes.

2. They allow a large amount of electricity to flow through them and hence are good conductors of electricity.

3. In aqueous solution or molten state, only ions are present.

Examples:

Strong acids : HCl, H₂SO₄ ,HNO₃

Strong bases : NaOH, KOH

Salts : NaCl, NaNO₃ , K2SO₄

Weak electrolytes :

1. The compound which in their aqueous solution or in fused state are partially ionised are called weak electrolytes.

2. They allow small amount of electricity to flow through them and hence are poor conductors of electricity.The compound which in their aqueous solution or in fused state are partially ionised are called weak electrolytes. In aqueous solution or molten state ions as well as unionised molecules are present. Examples :

Weak acids : CH₃COOH, H₂CO₃

Weak bases: NH₄OH, Ca(OH)₂

Salts: CH₃COONH₄ 

Weak Electrolytes: Carbonic acid, NH₄OH, Na₂CO₃ oxalic acid.

Dilute acids produce a large number of hydronium ions, so they behave like strong electrolytes. 

(a) Strong electrolyte: Dilute hydrochloric acid, dilute sulphuric acid, ammonium chloride, sodium acetate

(b) Weak electrolyte: Acetic acid, ammonium hydroxide

(c) Non-electrolyte: Carbon tetrachloride

(a) Reaction at anode during the electrolysis of very dilute sulphuric acid:

OH^- ⟶ OH + e^-

4OH ⟶ 2H₂O + O₂

(b) Reaction at anode during the electrolysis of aqueous copper sulphate solution

4OH^- ⟶ 4OH + 4e^-

4OH ⟶ 2H₂O +O₂

(c) Reaction at anode during the electrolysis of sodium chloride solution

2Cl^- ⟶ Cl₂ + 2^e-

(d) Reaction at anode during the electrolysis of fused lead bromide

Br^{- -} e^- ⟶ Br

Br + Br ⟶ Br₂

(e) Reaction at anode during the electrolysis of magnesium chloride (molten)

2Cl^- ⟶ Cl₂ + 2e^-

Concentrated (99%) sulphuric acid behaves like a weak electrolyte as it has very little hydronium ions in it. But when added to water, it becomes diluted and produces a large, number of hydronium ions. Now, it behaves like a stronger electrolyte and hence the bulb glows brightly.

1. As we descend the electro chemical series containing cations, the tendency of the cations to get reduced at the cathode increases.

2. The higher the concentration of an ion in a solution, the greater is the probability of its being discharged at its appropriate electrode.