Electrolysis Class 10 ICSE — Selina Chapter 6
Electrolysis Class 10 ICSE chemistry centres on one idea: electrical energy can drive a chemical change. This Selina Chapter 6 page explains the textbook section by section, in the book’s own order. You will find every definition, every electrode reaction, and the chapter PDF for revision. Worked patterns here use fresh numbers, never the textbook’s own examples.
Download Electrolysis Class 10 ICSE Chemistry Chapter 6 PDF
Download the Electrolysis Class 10 ICSE Chemistry chapter PDF from the Selina Concise textbook to revise offline or print for practice. It is the full chapter as printed in the book — 16 pages, 17 sections, 28 questions.
What is inside Chapter 6
16 pages · 17 sections · 4 worked examples · 28 exercise questions
| Section | Title |
|---|---|
| 6.1 | INTRODUCTION |
| 6.2 | SOME IMPORTANT TERMS |
| 6.3 | THEORY OF ELECTROLYTIC DISSOCIATION |
| 6.4 | CONDUCTION IN COMPOUNDS |
| 6.5 | CHARACTERISTICS OF ELECTROLYSIS |
| 6.5.1 | Electrolytic Dissociation |
| 6.5.2 | Ionisation |
| 6.5.3 | Comparison of ionisation and dissociation |
| 6.6 | ELECTROCHEMICAL (EC) SERIES |
| 6.6.1 | Electrochemical Series of metals |
| 6.7 | PREFERENTIAL OR SELECTIVE DISCHARGE OF IONS AT ELECTRODES |
| 6.8 | EXAMPLES OF ELECTROLYSIS |
| 6.9 | APPLICATIONS OF ELECTROLYSIS |
| 6.9.1 | Electroplating |
| 6.9.2 | Electrolytic refining of metals |
| 6.9.3 | Electrometallurgy |
| 6.10 | ACIDS, BASES AND SALTS AS ELECTROLYTES |
- Intext Questions: 5 questions
- Intext Questions: 9 questions
- EXERCISE: 14 questions
6.1 INTRODUCTION
Electrolysis joins two Greek roots. “Electro” means a flow of electrons or electricity. “Lysis” means separating, or bringing about a chemical change by passing electricity.
Not every conductor changes chemically. Metals like copper, aluminium and iron pass current without any change. They are conductors. Non-metals, apart from graphite, do not conduct. They are insulators.
Some compounds decompose when current passes. Copper chloride solution, for example, breaks into copper and chlorine. Such compounds are electrolytes. They conduct only in aqueous or molten state. Sugar solution never conducts and is a non-electrolyte.
The table below sets out the chapter’s first core distinction. This page sits inside the broader Class 10 Chemistry books collection.
| Metallic conductors | Electrolytic conductors |
|---|---|
| Single stream of electrons flows from negative to positive pole | Two streams: cations to cathode, anions to anode |
| Conduct in solid and molten state | Conduct only in aqueous solution or molten state |
| No change in form or composition; a physical process | New products form at electrodes; a chemical change |
6.2 SOME IMPORTANT TERMS
Electrolysis is the decomposition of a compound in aqueous solution or molten state using direct current. Electrolytes are compounds that conduct in these states and are decomposed. Examples include acids like H_2SO_4, HNO_3 and HCl, bases like NaOH, KOH and NH_4OH, and salts like NaCl, CuSO_4 and PbBr_2.
Non-electrolytes never conduct in any state. Distilled water, alcohol, kerosene, cane sugar, benzene, glucose and urea are examples. They contain only molecules, no ions.
Electrolytes split into two types. Strong electrolytes dissociate almost completely and let a bulb glow brightly. Weak electrolytes dissociate only partially and let it glow dimly.
| Strong electrolytes | Weak electrolytes |
|---|---|
| HCl, H_2SO_4, HNO_3 | Carbonic, acetic, oxalic acids |
| NaOH, KOH | Ca(OH)_2, NH_4OH |
| NaCl, PbBr_2, CuSO_4 | Sodium carbonate and bicarbonate |
An electrolytic cell (voltameter) converts electrical energy into chemical energy. An electrochemical cell does the reverse. The anode is the electrode connected to the positive terminal. The cathode connects to the negative terminal.
Ions are atoms or groups of atoms carrying charge. Cations are positive and migrate to the cathode. Anions are negative and migrate to the anode. The memory aid “A to A and C to C” fixes the direction: Anion to Anode, Cation to Cathode.
| Rule | Meaning |
|---|---|
| Anode → ADD = positive | Anode is the positive electrode |
| A to A | Anion (negative) goes to Anode |
| C to C | Cation (positive) goes to Cathode |
Oxidation in the electronic concept means losing electrons, as in \mathrm{Zn} - 2\mathrm{e}^- \rightarrow \mathrm{Zn}^{2+}. It also means gaining oxygen or losing hydrogen. Reduction means gaining electrons, as in \mathrm{Cu}^{2+} + 2\mathrm{e}^- \rightarrow \mathrm{Cu}. It also means losing oxygen or gaining hydrogen.
A worked pattern: in 2\mathrm{Mg} + \mathrm{O}_2 \rightarrow 2\mathrm{MgO}, magnesium is oxidised because it gains oxygen. Oxygen is the oxidising agent.
6.3 THEORY OF ELECTROLYTIC DISSOCIATION
Svante Arrhenius proposed his ionic theory in 1887. It rests on six points. An electrolyte dissociates into free mobile ions in water. Ions carry charge and conduct current. Conductivity depends on ion concentration. Positive and negative charges balance, keeping the solution electrically neutral. Non-electrolytes contain only molecules. Degree of dissociation measures how far an electrolyte breaks up.
The modern view differs. Arrhenius said water creates the ions. The modern concept says ions already exist in the solid, but electrostatic forces hold them immobile. Water breaks those forces and lets ions move.
6.4 CONDUCTION IN COMPOUNDS
Electrovalent compounds are aggregates of oppositely charged ions. Strong electrostatic forces lock these ions in place. Solid sodium chloride therefore cannot conduct, even though it contains ions.
Melting or dissolving breaks those forces. The ions become mobile and the compound conducts. Polar covalent compounds behave differently. HCl, NH_3 and water ionise in aqueous solution and conduct electricity.
6.5 CHARACTERISTICS OF ELECTROLYSIS
Eight characteristics define electrolysis. Cations migrate to the cathode; anions to the anode. Electrons gained at one electrode equal electrons lost at the other. Products form only at the electrode surfaces. Metals and hydrogen are liberated at the cathode; non-metals at the anode. The mass of product is proportional to the quantity of electricity, a statement called Tandey’s law. Electrolysis is a redox reaction. Only direct current causes electrolysis.
Sodium chloride shows the redox nature. In solution it dissociates as \mathrm{NaCl} \rightleftharpoons \mathrm{Na}^+ + \mathrm{Cl}^-. At the cathode, \mathrm{Na}^+ + \mathrm{e}^- \rightarrow \mathrm{Na}, a reduction. At the anode, \mathrm{Cl}^- - \mathrm{e}^- \rightarrow \mathrm{Cl}, then \mathrm{Cl} + \mathrm{Cl} \rightarrow \mathrm{Cl}_2, an oxidation.
6.5.1 Electrolytic Dissociation
Electrolytic dissociation is the process by which an ionic compound breaks into ions in the fused state or in aqueous solution. Sodium chloride is the standard example.
Solid NaCl contains Na^+ and Cl^-, but electrostatic attraction holds them fixed. No conduction occurs. In water, the polar water molecule pulls them apart. The slightly negative oxygen end pulls Na^+; the slightly positive hydrogen ends pull Cl^-. In the molten state, heat weakens the bonds and frees the ions.
6.5.2 Ionisation
Some covalent molecules form ions only when dissolved in water. That process is ionisation. Hydrogen chloride is the example.
In gas or pure liquid form, HCl does not conduct. It is polar covalent, with charge separation written \mathrm{H}^{\delta+} - \mathrm{Cl}^{\delta-}. In water, the negative oxygen of water pulls the positive hydrogen of HCl. The result is a hydronium ion and a chloride ion: (\mathrm{H}_3\mathrm{O})^+ + \mathrm{Cl}^-. No ions exist before water acts.
6.5.3 Comparison of ionisation and dissociation
These two processes differ in their starting material. Ionisation makes ions from neutral molecules. Polar covalent compounds like HCl, H_2CO_3 and NH_4OH show it. \mathrm{HCl} \xrightarrow{\mathrm{H}_2\mathrm{O}} \mathrm{H}^+ + \mathrm{Cl}^-.
Dissociation separates ions already present in an ionic compound. Electrovalent compounds like KCl and PbBr_2 show it. \mathrm{KCl} \rightarrow \mathrm{K}^+ + \mathrm{Cl}^-.
6.6 ELECTROCHEMICAL (EC) SERIES
Metal elements lose electrons from their outermost shell to form cations. For example, \mathrm{K} \rightarrow \mathrm{K}^+ + \mathrm{e}^-, \mathrm{Ca} \rightarrow \mathrm{Ca}^{2+} + 2\mathrm{e}^-, and \mathrm{Al} \rightarrow \mathrm{Al}^{3+} + 3\mathrm{e}^-.
The tendency to lose these valence electrons varies from metal to metal. The electrochemical series arranges metals in decreasing order of that tendency.
6.6.1 Electrochemical Series of metals
The series runs K, Ca, Na, Mg, Al, Zn, Fe, Ni, Sn, Pb, H, Cu, Hg, Ag, Au, Pt. Five rules follow. A higher metal displaces a lower one. Metals above hydrogen displace hydrogen from acids; those below cannot. Lower metals discharge more easily at the cathode. The easiest ion formers accept electrons back with most difficulty. Hydrogen sits with the metals because it forms a positive ion.
Anions also form a series: SO_4^{2-}, NO_3^-, Cl^-, Br^-, I^-, OH^- in increasing ease of discharge. Lower in the anion series means easier discharge at the anode.
A worked pattern: can iron displace copper from copper sulphate solution? Iron is above copper in the series, so it is more electropositive. The reaction \mathrm{Fe} + \mathrm{CuSO}_4 \rightarrow \mathrm{FeSO}_4 + \mathrm{Cu} produces a red precipitate of copper. For the same reason, zinc reacts with dilute acid but silver does not. Zinc sits above hydrogen; silver sits below it.
6.7 PREFERENTIAL OR SELECTIVE DISCHARGE OF IONS AT ELECTRODES
Selective discharge happens when two or more ions of the same charge compete at one electrode. One ion gets discharged in preference. Three factors decide the winner: position in the electrochemical series, concentration of ions, and nature of the electrodes.
The series usually wins. In dilute CuSO_4, Cu^{2+} discharges at the cathode before H^+ because copper sits lower. At the anode, OH^- discharges before SO_4^{2-}. The same pattern holds for dilute H_2SO_4 and dilute NaCl.
Concentration can override the series. In concentrated NaCl, the sheer number of Na^+ and Cl^- ions beats their position. Sodium and chlorine are produced instead of hydrogen and oxygen.
Electrode nature matters too. A copper anode dissolves as Cu^{2+} instead of letting OH^- discharge. A platinum anode is inert, so OH^- gives oxygen.
6.8 EXAMPLES OF ELECTROLYSIS
(I) Molten lead bromide uses a silica crucible with graphite electrodes, heated above 380°C, at 3 amperes. At the cathode, \mathrm{Pb}^{2+} + 2\mathrm{e}^- \rightarrow \mathrm{Pb}. At the anode, \mathrm{Br}^- - \mathrm{e}^- \rightarrow \mathrm{Br}, then \mathrm{Br} + \mathrm{Br} \rightarrow \mathrm{Br}_2. Grey-white lead forms; dark reddish-brown bromine fumes evolve.
(II) Acidified water in a Hoffman’s voltameter uses platinum electrodes. H^+ discharges at the cathode: \mathrm{H}^+ + \mathrm{e}^- \rightarrow \mathrm{H}, then \mathrm{H} + \mathrm{H} \rightarrow \mathrm{H}_2. OH^- discharges at the anode: \mathrm{OH}^- \rightarrow \mathrm{OH} + \mathrm{e}^-, then \mathrm{OH} + \mathrm{OH} \rightarrow \mathrm{H}_2\mathrm{O} + \mathrm{O}, and \mathrm{O} + \mathrm{O} \rightarrow \mathrm{O}_2. The gas ratio is 2:1 hydrogen to oxygen by volume. Acidity rises at the anode and falls at the cathode.
Dilute sulphuric acid is used because it is non-volatile.
(III) Copper sulphate with a platinum anode and a copper or platinum cathode. \mathrm{Cu}^{2+} + 2\mathrm{e}^- \rightarrow \mathrm{Cu} at the cathode. OH^- discharges at the anode to give oxygen. The blue colour fades as Cu^{2+} is used up.
(IV) Copper sulphate with copper electrodes. \mathrm{Cu}^{2+} + 2\mathrm{e}^- \rightarrow \mathrm{Cu} at the cathode. \mathrm{Cu} - 2\mathrm{e}^- \rightarrow \mathrm{Cu}^{2+} at the anode. The blue colour stays because the anode replaces every Cu^{2+} deposited. H^+, SO_4^{2-} and OH^- are spectator ions.
| Setup | Electrolyte | Electrodes | Cathode reaction | Anode reaction | Products |
|---|---|---|---|---|---|
| Molten lead bromide | PbBr_2 | Graphite | Pb^{2+} + 2e^- \rightarrow Pb | Br^- - e^- \rightarrow Br, then Br + Br \rightarrow Br_2 | Lead, bromine |
| Acidified water | H_2O + dil H_2SO_4 | Platinum | H^+ + e^- \rightarrow H, then H + H \rightarrow H_2 | OH^- \rightarrow OH + e^-, then O + O \rightarrow O_2 | Hydrogen (2 vol), oxygen (1 vol) |
| CuSO₄, platinum anode | CuSO_4 + H_2SO_4 | Pt anode, Cu/Pt cathode | Cu^{2+} + 2e^- \rightarrow Cu | OH^- \rightarrow OH + e^-, then O + O \rightarrow O_2 | Copper, oxygen |
| CuSO₄, copper electrodes | CuSO_4 | Copper both | Cu^{2+} + 2e^- \rightarrow Cu | Cu - 2e^- \rightarrow Cu^{2+} | Copper only |
6.9 APPLICATIONS OF ELECTROLYSIS
Electrolysis has three commercial applications. First, electroplating coats one metal with another. Second, electrorefining purifies metals. Third, electrometallurgy extracts reactive metals from their ores. Each gets its own section below.
6.9.1 Electroplating
Electroplating deposits a thin film of one metal on another using electricity. Two reasons drive it: decoration and protection from rusting. Brass objects get silver-plated for appearance. Iron tools get nickel, chromium or zinc to prevent rust.
Five conditions govern the process. The article sits at the cathode. The plating metal forms the anode and is replaced periodically. The electrolyte must contain ions of the plating metal. A low current over a longer time gives an even, thick deposit. Only direct current works.
Silver plating uses sodium argentocyanide, not silver nitrate. The double cyanide forms in two steps: \mathrm{AgNO}_3 + \mathrm{NaCN} \rightarrow \mathrm{AgCN} \downarrow + \mathrm{NaNO}_3, then \mathrm{AgCN} + \mathrm{NaCN} \rightarrow \mathrm{Na}[katex display="true"]\mathrm{Ag}(\mathrm{CN})_2[/katex]. At the cathode, \mathrm{Ag}^+ + \mathrm{e}^- \rightarrow \mathrm{Ag}. At the anode, \mathrm{Ag} - \mathrm{e}^- \rightarrow \mathrm{Ag}^+. Silver nitrate alone would deposit silver too fast and unevenly.
Nickel plating uses nickel sulphate. \mathrm{NiSO}_4 \rightleftharpoons \mathrm{Ni}^{2+} + \mathrm{SO}_4^{2-}. At the cathode, \mathrm{Ni}^{2+} + 2\mathrm{e}^- \rightarrow \mathrm{Ni}. At the anode, \mathrm{Ni} - 2\mathrm{e}^- \rightarrow \mathrm{Ni}^{2+}.
6.9.2 Electrolytic refining of metals
Electrolytic refining purifies metals electrolytically. Copper is the main example. Impure copper forms the anode, a thin strip of pure copper the cathode, and copper sulphate with dilute sulphuric acid the electrolyte.
At the cathode, \mathrm{Cu}^{2+} + 2\mathrm{e}^- \rightarrow \mathrm{Cu}. At the anode, \mathrm{Cu} - 2\mathrm{e}^- \rightarrow \mathrm{Cu}^{2+}. The deposited copper reaches 99.9% purity. Insoluble impurities like silver and gold collect near the anode as anode mud and are recovered.
6.9.3 Electrometallurgy
Electrometallurgy extracts metals by electrolysis. Reactive metals come from their fused salts. K, Na, Ca, Mg and Al sit high in the activity series and have strong affinity for oxygen. Less reactive metals like Zn, Fe, Pb, Cu, Hg and Ag are extracted with reducing agents. Pt and Au come by thermal decomposition.
Four examples follow the same pattern. Fused KBr gives K at the cathode and Br_2 at the anode. Fused NaCl gives Na and Cl_2. Fused MgCl_2 gives Mg and Cl_2. Alumina (Al_2O_3) with cryolite and fluorspar gives Al at the carbon-lined cathode and O_2 at the graphite anode.
6.10 ACIDS, BASES AND SALTS AS ELECTROLYTES
Acids and alkalis ionise when dissolved in water. Bases and salts dissociate when fused or dissolved. The degree of dissociation decides whether an electrolyte is strong or weak.
\alpha = \frac{\text{number of molecules dissociated}}{\text{total number of molecules}} \times 100Strong electrolytes include HCl, HNO_3, H_2SO_4, KOH, NaOH, LiOH, PbBr_2, CuCl_2 and AgNO_3. Weak electrolytes include acetic, formic and carbonic acids, Ca(OH)_2, Mg(OH)_2, NH_4OH, Na_2CO_3, KHCO_3 and lead acetate.
What to practise from Electrolysis Class 10 ICSE
The chapter carries three practice blocks. Work through them in order.
- Intext Questions: 5 questions on key terms, electrolysis definitions and the redox nature of the process.
- Intext Questions: 9 questions on electrolysis setups, ion discharge and electroplating terms.
- EXERCISE: 14 questions, including past board questions from 2004, 2005, 2007 and 2008.
The exercise map below links each EXERCISE question to the section that answers it.
| Exercise question | Section that answers it |
|---|---|
| Q1 (reasons a–j) | 6.8, 6.9.1, 6.10, 6.5.1, 6.9.3 |
| Q2 (classify substances) | 6.10 |
| Q3 (pure water) | 6.4 |
| Q4 (adding H_2SO_4) | 6.8 II |
| Q5 (complete the table) | 6.9.1, 6.9.2 |
| Q6 (electrolysis definition) | 6.1 |
| 004 Q1 (X and Y ions) | 6.2, 6.9 |
| 004 Q2 (particles in solution) | 6.2, 6.10 |
| 005 Q1 (Cu non-electrolyte, solid NaCl) | 6.2, 6.5.1 |
| 005 Q2 (gas at cathode) | 6.8 II |
| 006 Q1 (platinum anode, CuSO_4) | 6.8 III |
| 006 Q2 (copper in salt solutions) | 6.6.1 |
| 2007 Q1 (classify A–D) | 6.2, 6.10 |
| 2008 Q1–2 (electrode reactions, PbBr_2) | 6.2, 6.6.1, 6.7, 6.8 I |
Watch for three common mistakes. Sodium metal is not deposited from aqueous sodium chloride; hydrogen discharges first. Pure water does not conduct electricity; it needs an acid like dilute H_2SO_4 to ionise. Copper sulphate keeps its blue colour only when copper electrodes replace every Cu^{2+} ion.
You can also explore the wider Class 10 textbooks hub for other subjects.
Electrolysis Class 10 ICSE frequently asked questions
Why is hydrogen discharged at the cathode instead of sodium during electrolysis of aqueous sodium chloride?
Hydrogen sits much lower than sodium in the electrochemical series. Lower metals discharge more easily at the cathode. So H^+ gains electrons before Na^+. Sodium metal never deposits; hydrogen gas evolves instead.
What is the difference between ionisation and electrolytic dissociation?
Ionisation creates ions from neutral molecules of polar covalent compounds like HCl. Dissociation separates ions already present in electrovalent compounds like KCl. Water acts on both, but only ionisation forms the ions in the first place.
Why does the blue colour of copper sulphate fade with platinum electrodes but stay unchanged with copper electrodes?
With platinum, Cu^{2+} deposits at the cathode and nothing replaces it at the anode, so the blue colour fades. With copper electrodes, the copper anode dissolves as Cu^{2+} and replaces every ion deposited. The Cu^{2+} count stays constant, so the colour holds.
Why is silver nitrate not used directly as the electrolyte for silver electroplating?
Silver nitrate deposits silver too fast. The coating comes out uneven and rough. Sodium argentocyanide releases Ag^+ slowly and evenly, giving a smooth firm coat.
Which electrolysis class 10 icse questions should I practise from this chapter?
Start with the 5 Intext Questions on key terms. Then the 9 Intext Questions on electrolysis setups. Finish with the 14 EXERCISE questions, which include past board questions from 2004 to 2008. The exercise map above links each one to the section that answers it.
You can verify the syllabus requirements for this chapter on the official CISCE website.
Reference: ICSE Class 10 Chemistry textbook material, chapter 6: Electrolysis — CISCE-aligned.
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