Selina ICSE Class 10 Chemistry Solutions Chapter 6 Electrolysis

Selina ICSE Solutions

Intext– Question-1

Question 1: Fill In The Blanks:

(a) Powdered sodium chloride (common salt) does not conduct an electric current, but it does so when ……………. or when ……………..
(b) Molten lead bromide conducts electricity. It is called an It is composed of
Lead ……………. and bromide …………….. The lead ions are charged and are
called …………….. The bromide ……………. are charged and are called ……………..
(c) Substances which conduct electricity in the solid state are generally ……………..
(d) The electron releasing tendency of zinc is …………… than that of copper.
(e) A solution of HCl gas in water conducts electricity because , but a solution
Of HCl gas in toluene does not conduct an electric current because …………….
Solution 1:

(a) Powdered sodium chloride (common salt) does not conduct an electric current, but it does so when dissolved in water or when melted.
(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 in toluene.

Question 2: Define the following terms:
(a) Electrolysis,
(b) Non-electrolyte,
(c) Cation and anion,
(d) Weak electrolyte,
Solution 2:
(a) Electrolysis: Electrolysis is the decomposition of a chemical substance in aqueous solutions or in a molten state, which is followed by a chemical change, utilizing direct electric current.
(b) Non-electrolyte: A chemical that does not enable an electric current to pass through it in either solution or molten form.
(c) Cation and anion: Cations are atoms with a positive charge. Anions are atoms with a negative charge.
Anions are atoms that have a negative charge. One that would be attracted to the anode in electrolysis.
(d) Weak electrolyte: Weak electrolytes are electrolytes that allow a tiny amount of electricity to flow through them and are partially dissociated in fused or aqueous solution.

Question 3: What is the difference between:
(a) Modern explanation and Arrhenius explanation for the theory of electrolysis:
(b) Electrolytic dissociation and ionization:
(c) A cation and an anion,
Solution 3:
(a) Difference between the Modern and Arrhenius explanations for electrolysis theory:
Water ionizes electrolytes, according to Arrhenius, but modern theory explains that electrolytes are ionic even when solid, and their ions are kept in place by strong electrostatic forces, making them immobile. By breaking the electrostatic forces, water makes these ions mobile.
(b) Electrolytic dissociation and ionization:

1.  The formation of positively or negatively charged ions from molecules that are not in an ionic state at the start.1. Ion separation is the separation of ions that are already present in an ionic composition.
2. Ionization occurs in polar covalent molecules. HCl, H2CO3, NH4OH and so forth.2. Dissociation is seen in electrovalent substances. For example, potassium chloride,  lead bromide, and so on.

(c) A cation and anion:

1. Ions that have a positive charge.1. Ions with a negative charge.
2. During electrolysis, migrate to the cathode.2. During electrolysis, migrate to the anode.
3. Gain one electron from the cathode and become a neutral atom by being reduced.3. As a result of losing electrons to the anode, the atom is oxidized and becomes a neutral atom.

(d) Electrolytic and thermal dissociation: Electrolytic dissociation is the dissociation of an electrovalent chemical into ions in a fused or aqueous solution state.
Thermal dissociation is the reversible breakdown of a chemical molecule into simpler compounds when it is heated. One example is the breakdown of ammonium chloride into ammonia and hydrogen chloride. They recombine to produce salt as they cool.

Question 4: Name:
(a) A salt which is a weak electrolyte.
(b) A base which is a weak electrolyte.
(c) An inert electrode and an active electrode.
(d) A positively charges non-metallic ion.
(e) the electrode at which reduction occurs.
(f) a non-metallic element which is a conductor of electricity.
Solution 4:
(a) Sodium carbonate is a salt which is a weak electrolyte.
(b) NH4OH is a base which is a weak electrolyte.
(c) An inert electrode is graphite and active electrode is silver.
(d) H+ is a positively charges non-metallic ion.
(e) Electrode is cathode at which reduction occurs.
(f) Graphite is a non-metallic element which is a conductor of electricity.

Question 5: Electrolysis is a redox process. Explain.
Solution 5:
The process of electrolysis is a redox reaction. The reduction of cations occurs at the cathode as they obtain electrons, whereas the oxidation of anions occurs at the anode as they lose electrons and become neutral.
Example: Dissociation of sodium chloride during electrolysis.
NaCl ⇌ Na+ + Cl-
Cathode : Na+ + e- ⟶ Na (reduction) Cl-−e
⟶ Cl (oxidation)
Cl + Cl ⟶ Cl2
Overall reaction: 2NaCl ⟶ 2Na + Cl2

Intext– Question– 2

Question 1: Name two substances in each case:
(a) Contain only molecules,
(b) Contain only ions,
(c) Contain ions as well as molecules.
Solution 1:
(a) Substances that contain only molecules are Glucose, Kerosene.
(b) Substances that contain only ions are NaCl and NaOH.
(c) Substances that contain ions as well as molecules are CH3COOH and NH4OH.

Question 2: Explain the following:
(a) A solution of cane sugar does not conduct electricity, but a solution of sodium chloride is a good conductor,
(b) Hydrochloric acid is a good conductor of electricity,
(c) During the electrolysis of an aqueous solution of NaCI, hydrogen ion is reduced at the cathode and not the sodium ion though both Na+ and H+ ions are present in the solution.
Solution 2:
(a) Cane sugar is a molecule-only substance that does not contain any ions, even in solution. As a result, it is not an electrical conductor. Sodium chloride solution, on the other hand, has free mobile ions and permits electric current to travel through it. As a result, it is an excellent conductor of electricity. Substances having only molecule don’t conduct electricity but substances having ions conduct electricity.
(b) Hydrochloric acid is a powerful electrolyte that totally dissociates in water. Electric current can travel through the solution because it contains free mobile ions. As a result, hydrochloric acid is an excellent electrical conductor.
(c) Hydrogen is at the bottom of the electrochemical chain, whereas sodium is at the top. This is due to the fact that H+ ions discharge more quickly at the cathode during electrolysis than Na+ ions and acquire electrons more readily.
As a result, the H+ ion, rather than the Na+ ion, is decreased at the cathode.

Question 3: Among Zn and Cu, which would occur more readily in nature as metal and which as ion?
(a) Why cannot we store AgNO3 solution in copper vessel?
(b) Out of Cu and Ag, which is more active?
Solution 3:
(a) In nature, Zn is found as an ion, whereas Cu is found as a metal.
(b) Copper is more reactive than silver because it is higher in the electrochemical series than silver. As a result, copper takes the place of silver in silver nitrate. As a result, we are unable to hold AgNO3 solution in a copper vessel.
Cu + AgNO3 ⟶ Cu(NO3)2 + 2Ag
(a) Copper has a higher activity level than silver.

Question 4: How would you change a metal like Cu in to its ions?
(a) How would you change Cu2+ ion to Cu?
Solution 4:
(a) By using a more reactive metal to treat the salt.
(b) By supplying two electrons to Cu + 2Cu+2 + 2e- ⟶ Cu

Question 5: A solution of caustic soda (NaOH) in water or when fused, conducts an electric current. What is the similarity in these two cases?
Solution 5:
The slightly negatively charged oxygen atoms of the polar water molecule pull on the positively charged sodium ions in the aqueous state. The mildly charged hydrogen atoms of water exert a similar force on the negatively charged chloride ions. As a result, the ions in solution become free. These free ions are electrical conductors.
The high temperatures required to melt the solid weaken the link between the particles in the molten state, allowing the ions to escape.

Question 6: During electrolysis of an aqueous solution of sulphuric acid between platinum electrodes, two types of anions migrate towards the anode but only one of them is discharged:
(a) Name the two anions,
(b) Name the main product of the discharge of anion at the anode and write the anode reaction,
(c) Name the product at the cathode and write the reaction.
(d) How you notice any change in colour. State why?
(e) Why this electrolysis, is considered as an example of catalysis?
Solution 6:
(a)SO2− and OH are two anions.
(b) At the anode, OH- is discharged, and the major result of this discharge is O2.
OH-⟶ OH + e- 4OH ⟶ 2H2O + O2
(c) (c) At the cathode, the result is hydrogen. The reaction is as follows:
H+ +e- ⟶ H
H+H ⟶ H2
(d) There is no change in colour.
(e) Because dilute sulphuric acid catalyses the dissociation of water molecules into ions, acidified water electrolysis is considered a type of catalysis.

Question 7: An electrolytic cell is setup using two platinum electrodes and an aqueous solution of copper
(II) sulphate,
(a) Draw a labeled diagram of the electrolytic cell, (b) Name the ions present in the cell,
(c) Name the ions migrating towards the anode,
(d) Name the ions migrating towards the cathode,
(e) Name the ions which will not be discharged at electrodes during electrolysis,
(f) Write the reaction at the cathode,
(g) Write the reaction at the anode,
(h) Name the spectator ion in the solution.
Solution 7:
(a) (a) An electrolytic cell labelled schematic is as follows:
(b) The ions present in the cell are Cu2+, H+, SO2-,OH.
(c) SO42-and OHions both migrate towards anode.
(d) Both Cu2+ and H+ ions migrate towards cathode.
(e) SO42- and H+ will not discharge at electrodes.
(f) Reaction at cathode:
Cu+2 + 2e ⟶ Cu
(g) Reaction at anode:
OH – e ⟶ OH
2OH + 2OH ⟶ 2H2O + O2
(h) The spectator ions are sulphate ions, which do not change during the process.

Question 8: State the electrode reaction at the anode during electrolysis of:
(a) Very dilute sulphuric acid,
(b) Aqueous copper sulphate solution
(c) sodium chloride solution,
(d) Fused lead bromide,
(e) Magnesium chloride (molten).
Solution 8:
(a) Anode reaction during the electrolysis of very dilute sulphuric acid:
OH⟶ OH + e
4OH ⟶ 2H2O + O2
(b) Anode reaction during the electrolysis of aqueous copper sulphate solution
4OH ⟶ 4OH + 4e
4OH ⟶ 2H2O + O2
(c) Anode reaction during the electrolysis of sodium chloride solution
2Cl ⟶ Cl2 + 2e
(d) Anode reaction during the electrolysis of fused lead bromide
Br – e ⟶ Br
Br + Br ⟶ Br2
(e) Anode reaction during the electrolysis of magnesium chloride (molten)
2Cl ⟶ Cl2 + 2e

Question 9: Choosing only words from the following list, write down the appropriate words to fill in the blanks (a) to (e) below: anions, anode, cathode, cations, electrode, electrolyte, nickel, voltameter.
The electroplating of an article with nickel requires an (a) which must be a solution containing (b) ions. The article to be plated is placed as the (c) of the cell in which the plating is carried out. The (d) of the cell is made from pure nickel. The ions that are attracted to the negative electrode and discharged are called (e).
Solution 9:
(a) Electrolyte
(b) Nickel
(c) Cathode
(d) Anode
(e) Cations


Question 1: Give reasons for the following:
(a) Electrolysis of molten lead bromide is considered to be a reaction in which oxidation and reduction go side by side, i.e., a redox reaction.
(b) The blue colour of aqueous copper sulphate fades when it is electrolysed using platinum electrodes.
(c) Lead bromide under goes electrolytic dissociation in the molten state but is a non-electrolyte in the solid state.
(d) Aluminium is extracted from its oxide by electrolytic reduction and not by convectional reducing agents.
(e) The ratio of hydrogen and oxygen formed at the cathode and anode is 2:1 by volume.
(f) In the electrolysis of acidified water, dilute sulphuric acid is preferred to dilute nitric acid for acidification.
(g) Ammonia is unionized in the gaseous state but in the aqueous solution, it is a weak electrolyte.
(h) A graphite anode is preferred to other inert electrodes during electrolysis of fused lead bromide.
(i) For electroplating with silver, silver nitrate is not used as electrolyte.
(j) Carbon tetrachloride is a liquid but does not conduct electricity.
Solution 1:
(a) During the electrolysis of lead bromide, electrons are lost at the anode by bromine and gained at the cathode by lead. As a result, oxidation and reduction coexist. As a result, it’s a redox reaction.
PbBr2 ⟺ Pb+2  +  2Br
(b) As the concentration of Cu+2 ions decreases, the blue colour of copper ions diminishes, and the solution eventually becomes colourless.
(c) In the molten state, lead bromide dissociates into ions, but it does not dissociate in the solid state. When lead bromide is molten, the ions become free, but when it is solid, the ions are not free because they are packed tightly together due to electrostatic forces. As a result, in the molten state, lead bromide undergoes electrolytic dissociation.
(d) Because aluminium has a high affinity for oxygen, it is unaffected by reducing agents. As a result, electrolytic reduction is used to separate it from its oxide.
(e) Electrolytic reactions need 4H+1 at the cathode and 4OH at the anode, resulting in the production of two molecules of water at the anode. At the cathode and anode, two molecules of hydrogen and one molecule of oxygen are freed for every two molecules of water.
2H2 Current 2H2 [cathode]  +  O2 [anode]
(f) This is due to the fact that HNO3 is flammable.
(g) Ammonia is a covalently bound substance. In the gaseous state, it is unionized, but in aqueous solution, it yields NH4OH, which is a weak electrolyte that dissociates into ions.
(h) Bromine vapours have no effect on graphite.
(i) Silver nitrate is not utilized as an electrolyte for silver electroplating because the silver deposition is very quick and hence not very smooth and uniform.
(j) Carbon tetrachloride is a liquid and does not conduct electricity because it is a covalent compound ant there are no free ions present and contain only molecules.

Question 2: Classify the following substance under three headings:
(a) Strong electrolytes
(b) Weak electrolytes
(c) Non electrolytes.
Acetic acid, ammonium chloride, ammonium hydroxide, carbonate tra-chloride, dilute hydrochloric acid, sodium acetate, dilute sulphuric acid.
Solution 2:
(a) Strong electrolytes include dilute hydrochloric acid, dilute sulphuric acid, ammonium chloride, and sodium acetate.
(b) Weak electrolytes include acetic acid and ammonium hydroxide.
(c) Carbon tetrachloride is a non-electrolyte.

Question 3: Write down the words or phrases from the brackets that will correctly fill in the blanks in the following sentences:
(a) Pure water consists entirely of _ (ions/molecules).
(b) We can expect that pure water (will/will not) normally conduct electricity.
Solution 3:
(a) Molecules
(b) Will not

Question 4: To carry out the so-called “electrolysis of water”. Sulphuric acid is added to water. How does the addition of sulpuric acid produce a conducting solution?
Solution 4:
Water is made up entirely of molecules and is a non-conductor of electricity. It can be electrolytically destroyed by adding trace amounts of dilute sulphuric acid, which dissociates into H+ and SO42- ions and aids in the dissociation of water into H+ and OH, despite the fact that water is a polar solvent.

Question 5: Copy and complete the following table which refers to two practical applications of electrolysis

Silver plating of a spoon Solution of potassium argento cyanide
Purification of copper  

Solution 5:

Silver plating of a spoonPlate of pure cleanSolution of potassium argento cyanideArticle to be electroplated
Purification of copperImpure copperSolution of copper sulphate And dilute sulphuric acidThin strip of pure copper

Question 6: Complete the sentence by choosing correct words given in brackets.
Electrolysis is the passage of
(electricity/ electrons)through a liquid or a solution accompanied by a (Physical
/chemical) change.
Solution 6:
Electricity, Chemical

Question : Element X is an metal with a valency 2. Element Y is a non-metal with a valency 3.
(a) Write equations to show how X and Y form ions?
(b) If Y is a diatomic gas, write the equation for the direct combination of X and Y to form a compound,
(c) Write two applications of electrolysis in which the anode diminishes in mass,
(d) 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 ………….. and Y at the ………………. of the electrolytic cell. (Provide the missing words)
Solution :

(c) (i) It’s used for electroplating metals, for example.
(ii) It’s also utilized in metal purification.
(d) Cathode, Anode

Question 2: What kind of particles will be found in a liquid compound which is a non–electrolyte?
(a) If HX is a weak acid, what particles will be present in its dilute solution apart from those of water?
(c) At ions are formed by …………….. (loss/gain) of electrons and anions are formed by …………………
(loss/gain) of electrons. (Choose the correct word to fill in the blanks).
(d) What ions must be present in a solution used for electroplating a particular metal?
(e) Explain how electrolysis is an example of redox reaction.
Solution 2:
(a) Non-electrolyte contains molecules.
(b) Molecules of HX and H+ and X ions.
(c) Loss
(d) The electrolyte used for the purpose must contain the ions of metal which is to be electroplated on the article.
(e) At the cathode, cations are reduced as they receive electrons and become neutral atoms, whereas at the anode, anions are oxidised as they lose electrons and become neutral.
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

Question : 1. Explain why:
(a) Cu, though a good conductor of electricity is a non electrolyte,
(b) Solid sodium chloride does not allow electricity to pass through?
Solution :
(a) Copper though a good conductor of electricity is a non electrolyte as copper has no mobile electrons in the solid state and an electrolyte should dissociate into oppositely charged ions to conduct electricity.
(b) Solid sodium chloride does not allow electricity to pass through because of high electrostatic forces of attraction, the Na+ and Cl – ions are not free in solid sodium chloride. As a result, when the electric field is disrupted, the ions are unable to migrate to any significant extent. As a result, there is no current.

Question 2: Name the gas released at cathode when acidulated water is electrolyzed.
Solution 2:
When acidulated water is electrolyzed, hydrogen gas is emitted at the cathode.

Question : Copper sulphate solution is electrolyzed using a platinum anode.
(a)Study the diagram given alongside and answer the following questions:
(i) Give the name of the electrodes A and B.
(ii) Which electrode is the oxidizing electrode?
(c) A strip of copper is placed in four different colourless salt solutions. They are KNO3, AgNO3, Zn(NO3)2, Ca(NO3)2. Which one of the solutions will finally turn blue?
Solution :
(a) (i) Electrode A is known as a platinum anode, whereas electrode B is known as a platinum or copper cathode.
(ii) The anode serves as an oxidizer electrode.
(b) AgNO3 solution will turn blue.

Question : Choose A, B, C or D to match the descriptions (i) to (v) below. Some alphabets may be repeated.
A. non-electrolyte
B. strong electrolyte
C. weak electrolyte
D. metallic conductor
(i) Molten ionic compound,
(ii) Carbon tetrachloride,
(iii) An aluminum wire,
(iv) A solution containing solvent molecules solute molecules and ions formed by the dissociation of solute molecules.
(v) A sugar solution with sugar molecules and water molecules.
Solution :
(i) Molten ionic compound: Strong electrolytes
(ii) Carbon tetrachloride: Non-electrolyte
(iii) An aluminum wire: Metallic conductor
(iv) A solution containing solvent molecules, solute molecules and ions formed by dissociation of solute molecules: Weak electrolyte
(v) A sugar solution with sugar molecules and water molecules: Non – electrolyte

Question : Here is an electrode reaction: Cu ⟶ Cu2+ + 2e
At which electrode (anode or cathode) would such a reaction take place? Is this an example of oxidation or reduction?
(a) A solution contains magnesium ions (Mg2+), iron (II) ions (Fe2+) and copper ions (Cu2+). On passing an electric current through this solution, which ions will be the first to be discharged at the cathode? Write the equation for the cathode reaction.
(b) Why is carbon tetrachloride, which is a liquid, of the following takes place?
Solution :
(a) The reaction occurs at the anode.
(b) Cu+2 will discharge easily at cathode. Reaction at cathode:
Cu+2 +2e ⟶Cu
(c) Carbon tetrachloride is a covalent molecule, it is a non-electrolyte. As it does not ionise, it could not conduct electricity.

Question 2: During the electrolysis of molten lead bromide, which of the following takes place?
A. Bromine is released at the cathode,
B. Lead is deposited at the anode,
C. Bromine ions gain electrons,
D. Lead is deposited at the cathode.
Solution 2:
During the electrolysis of molten lead bromide, lead is deposited at cathode.

Selina ICSE Class 10 Chemistry Solutions Chapter 6 Electrolysis