Selina Concise Solutions for ICSE Class 10 Chemistry Chapter 6 Electrolysis

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 ……….......
Answer: (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.
In simple words: Solid salt cannot conduct electricity because its ions are stuck together. When we dissolve it in water or melt it, the ions become free to move and carry electric current.

📝 Teacher's Note: Use a simple demonstration with a battery, bulb, and salt solution to show conductivity. Compare with dry salt to emphasize the importance of free-moving ions for electrical conduction.

🎯 Exam Tip: Remember the key phrase "free mobile ions" - this is what examiners look for when explaining electrical conductivity in electrolytes.

Question 2. Define the following terms:
(a) Electrolysis,
(b) Non-electrolyte,
(c) Cation and anion,
(d) Weak electrolyte,
Answer: (a) Electrolysis: It is the process of decomposition of a chemical compound in aqueous solutions 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 and anion: Atoms which carry positive charge are called cations. Atoms which carry negative charge are called anions.
(d) Weak electrolyte: Electrolytes which allow small amount of electricity to flow through them and are partially dissociated in fused or aqueous solution are called weak electrolyte.
In simple words: Electrolysis breaks down compounds using electricity. Cations are positive ions that move to the negative electrode, while anions are negative ions that move to the positive electrode.

📝 Teacher's Note: Use the memory trick "CAT-ion goes to CAT-hode" and "AN-ion goes to AN-ode" to help students remember ion movement during electrolysis.

🎯 Exam Tip: Always mention "direct electric current" when defining electrolysis - it's a key marking point that distinguishes it from other chemical processes.

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,
Answer: (a) Difference between Modern explanation and Arrhenius explanation for the theory of electrolysis:
Arrhenius considered that water ionizes electrolytes but Modern theory explained that electrolytes are ionic even in solid state and their ions are held by strong electrostatic forces which make them immobile. Water renders these ions mobility by breaking the electrostatic forces.
(b) Difference between electrolytic dissociation and ionization :

(c) A cation and anion:

(d) Electrolytic dissociation and thermal dissociation:
Electrolytic dissociation is the dissociation of an electrovalent compound into ions in the fused state or in aqueous solution state.
Thermal dissociation: Reversible breakdown of a chemical compound into simpler substances by heating it. The splitting of ammonium chloride into ammonia and hydrogen chloride is an example. On cooling, they recombine to form the salt.
In simple words: Ionization creates new ions from molecules, while dissociation separates ions that already exist. Think of ionization as breaking a friendship to create enemies, and dissociation as separating friends who were already there.

📝 Teacher's Note: Use practical examples like sugar (ionizes) vs salt (dissociates) to make the distinction clear. Demonstrate with actual solutions to show the difference.

🎯 Exam Tip: Remember: HCl ionizes (forms new ions), NaCl dissociates (separates existing ions). This distinction often appears in exam questions.

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.
Answer: (a) Sodium carbonate
(b) \( NH_4OH \)
(c) An inert electrode: graphite and Active electrode: silver
(d) \( H^+ \)
(e) Electrode is cathode
(f) Graphite
In simple words: Weak electrolytes partially break into ions, inert electrodes don't react during electrolysis, and reduction (gaining electrons) always happens at the cathode.

📝 Teacher's Note: Emphasize that graphite is special among non-metals because of its unique structure that allows electron flow. Show students actual graphite from a pencil to make it relatable.

🎯 Exam Tip: Remember "RED CAT" (Reduction at Cathode) and "AN OX" (Anode Oxidation) to recall which process occurs at which electrode.

Question 5. Electrolysis is a redox process. Explain.
Answer: Electrolysis is a redox process. The reaction at the cathode involves reduction of cations as they gain of electrons while the reaction at anode involves oxidation of anions as they loss of electrons to become neutral.
Example: Dissociation of sodium chloride during electrolysis.
\( NaCl \leftrightarrow Na^+ + Cl^- \)
Cathode: \( Na^+ + e^- \rightarrow Na \) (reduction)
Anode: \( Cl^- - e^- \rightarrow Cl \) (oxidation)
\( Cl + Cl \rightarrow Cl_2 \)
Overall reaction: \( 2NaCl \rightarrow 2Na + Cl_2 \)
In simple words: During electrolysis, both reduction (gaining electrons) and oxidation (losing electrons) happen simultaneously at different electrodes, making it a complete redox process.

📝 Teacher's Note: Use the mnemonic "OIL RIG" (Oxidation Is Loss, Reduction Is Gain of electrons) and relate it to the anode and cathode respectively.

🎯 Exam Tip: Always write both half-reactions separately and then the overall reaction to show complete understanding of the redox process in electrolysis.

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.
Answer: (a) Glucose, Kerosene
(b) NaCl and NaOH
(c) \( CH_3COOH \) and \( NH_4OH \)
In simple words: Some substances have only molecules (like sugar), some have only ions (like salt), and some have both molecules and ions mixed together (like weak acids).

📝 Teacher's Note: Use everyday examples - sugar water (molecules only), salt water (ions only), and vinegar (both) to make this concept relatable to students' daily experience.

🎯 Exam Tip: Remember that weak electrolytes always contain both ions and molecules, while strong electrolytes contain only ions in solution.

Question 2. Explain the following:
(a) A solution of cane sugar does not conduct electricity, but a solution of 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.
Answer: (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.
In simple words: Sugar molecules don't break into charged particles, so no electricity flows. Salt and acids break into charged ions that can carry electric current. In competition between ions, hydrogen wins over sodium because it's easier to reduce.

📝 Teacher's Note: Demonstrate with a simple conductivity meter using sugar water vs salt water. Explain that the electrochemical series is like a "queue" where some ions get priority over others.

🎯 Exam Tip: Always mention "free mobile ions" when explaining electrical conductivity. For preferential discharge, refer to the electrochemical series and mention relative positions.

Question 3.
(a) Among Zn and Cu, which would occur more readily in nature as metal and which as ion?
(b) Why cannot we store \( AgNO_3 \) solution in copper vessel?
(c) Out of Cu and Ag, which is more active?
Answer: (a) Zn occurs readily as ion whereas Cu occurs more readily as metal in nature.
(b) Copper is above silver in the electrochemical series and is thus more reactive than silver. So, copper displaces silver from silver nitrate. Hence, we cannot store \( AgNO_3 \) solution in copper vessel.
\( Cu + AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag \)
(c) Copper is more active than Ag.
In simple words: Reactive metals like zinc exist as ions in nature, while less reactive metals like copper exist as pure metals. Copper can "steal" silver from its compounds because copper is more reactive.

📝 Teacher's Note: Connect this to real-life examples like why gold and silver are found as pure metals in nature, while iron is found as ores (compounds). Demonstrate displacement reactions using actual metal pieces if possible.

🎯 Exam Tip: Remember the reactivity series - more reactive metals displace less reactive ones. Always write the balanced chemical equation for displacement reactions.

Question 4.
(a) How would you change a metal like Cu into its ions?
(b) how would you change \( Cu^{2+} \) ion to Cu?
Answer: (a) By treating its salt with a more reactive metal.
(b) By supplying two electrons to \( Cu^{+2} \)
\( Cu^{+2} + 2e^- \rightarrow Cu \)
In simple words: To make metal ions from metals, use a more reactive metal to "kick out" the less reactive one. To get metal back from ions, just give the ions their missing electrons.

📝 Teacher's Note: Emphasize that this is the principle behind metal extraction from ores - we either use more reactive metals or provide electrons through electrolysis.

🎯 Exam Tip: For ion to metal conversion, always write the electron gain equation showing the exact number of electrons needed.

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?
Answer: 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 hydroxide 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.
In simple words: In both cases, the ions become free to move. Water helps separate the ions in solution, while high heat breaks the bonds in molten state.

📝 Teacher's Note: Use the analogy of people stuck in a crowded room - water acts like creating more space for movement, while heat acts like weakening the connections between people.

🎯 Exam Tip: The key similarity is "free mobile ions" - mention this phrase and explain how it's achieved differently in aqueous vs molten states.

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?
Answer: (a) Two anions are \( SO_4^{2-} \) and \( OH^- \).
(b) \( OH^- \) is discharged at anode and the main product of the discharge of \( OH^- \) is \( O_2 \)
Reaction is :
\( OH^- \rightarrow OH + e^- \)
\( 4OH \rightarrow 2H_2O + O_2 \)
(c) The product formed at cathode is hydrogen. The reaction is :
\( H^+ + e^- \rightarrow H \)
\( H + H \rightarrow H_2 \)
(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.
In simple words: Water splits into hydrogen and oxygen gases during this electrolysis. Sulphuric acid acts like a helper (catalyst) that makes water conduct electricity without getting used up itself.

📝 Teacher's Note: Explain that \( SO_4^{2-} \) ions are too stable to discharge, so \( OH^- \) ions (from water) discharge instead. This is a classic example of preferential discharge.

🎯 Exam Tip: Remember that this electrolysis essentially splits water into \( H_2 \) and \( O_2 \). The acid just helps conduction and doesn't get consumed - that's why it's catalysis.

Question 7. An electrolytic cell is set up using two platinum electrodes and an aqueous solution of copper (II) sulphate,
(a) draw a labelled 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.
Answer: (a) Labelled diagram of electrolytic cell is shown with current source connected to platinum electrodes (anode and cathode) immersed in \( CuSO_4 \) solution. Anions \( (SO_4^{2-}) \) migrate to anode, cations \( (Cu^{2+}) \) migrate to cathode.
(b) The ions present in the cell are \( Cu^{2+} \), \( H^+ \), \( SO_4^{2-} \), \( OH^- \).
(c) \( SO_4^{2-} \) and \( OH^- \) ions both migrate towards anode.
(d) Both \( Cu^{2+} \) and \( H^+ \) ions migrate towards cathode.
(e) \( SO_4^{2-} \) and \( H^+ \) will not discharge at electrodes.
(f) Reaction at cathode: \( Cu^{2+} + 2e^- \rightarrow Cu \)
(g) Reaction at anode: \( OH^- - e^- \rightarrow OH \)
2\( OH + 2OH \rightarrow 2H_2O + O_2 \)
(h) Sulphate ions are the spectator ions because they do not change in the reaction.
In simple words: During electrolysis, copper metal forms at the negative electrode while oxygen gas forms at the positive electrode. The sulphate ions just watch without participating in the reactions.

📝 Teacher's Note: Use the diagram to explain ion movement clearly — draw arrows showing positive ions moving to negative electrode and vice versa. Many students confuse which ions move where, so emphasize the "opposite attracts" rule.

🎯 Exam Tip: Always mention both possible ions at each electrode (Cu²⁺ and H⁺ at cathode, SO₄²⁻ and OH⁻ at anode) then explain which one actually discharges based on discharge potential.

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).
Answer: (a) Reaction at anode during the electrolysis of very dilute sulphuric acid:
\( OH^- \rightarrow OH + e^- \)
4\( OH \rightarrow 2H_2O + O_2 \)
(b) Reaction at anode during the electrolysis of aqueous copper sulphate solution:
4\( OH^- \rightarrow 4OH + 4e^- \)
4\( OH \rightarrow 2H_2O + O_2 \)
(c) Reaction at anode during the electrolysis of sodium chloride solution:
2\( Cl^- \rightarrow Cl_2 + 2e^- \)
(d) Reaction at anode during the electrolysis of fused lead bromide:
\( Br^- - e^- \rightarrow Br \)
\( Br + Br \rightarrow Br_2 \)
(e) Reaction at anode during the electrolysis of magnesium chloride (molten):
2\( Cl^- \rightarrow Cl_2 + 2e^- \)
In simple words: At the anode, negative ions lose electrons to form neutral atoms or molecules. Different solutions give different products — oxygen from water-based solutions, chlorine from chlorides, bromine from bromides.

📝 Teacher's Note: Help students remember that anodes attract anions (negative ions) and these ions lose electrons (oxidation). Use the mnemonic "OILRIG" — Oxidation Is Loss, Reduction Is Gain of electrons.

🎯 Exam Tip: For aqueous solutions, always consider both the salt ions and water ions. Write which ion discharges preferentially based on ease of discharge — hydroxide ions discharge more easily than sulphate ions.

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)________
Answer: (a) Electrolyte
(b) Nickel
(c) Cathode
(d) Anode
(e) Cations
In simple words: In electroplating, we need a conducting solution with metal ions, the object to be plated acts as the negative terminal, and a pure metal rod acts as the positive terminal.

📝 Teacher's Note: Demonstrate electroplating with a simple setup using copper sulphate solution and copper electrodes. Students can see the copper deposit forming on the cathode, making the concept concrete.

🎯 Exam Tip: Remember that the object being plated is always the cathode (negative electrode) and the pure metal source is always the anode (positive electrode) in electroplating.

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 undergoes electrolytic dissociation in the molten state but is a nonelectrolyte in the solid state.
(d) Aluminium is extracted from its oxide by electrolytic reduction and not by conventional 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.
Answer: (a) During electrolysis of lead bromide, there is loss of electrons at anode by bromine and gain of electrons at cathode by lead. Thus oxidation and reduction go side by side. Therefore, it is a redox reaction. \( PbBr_2 \rightleftharpoons Pb^{2+} + 2Br^- \)
(b) The blue colour of copper ions fades due to decrease in \( Cu^{2+} \) ions and finally the solution becomes colourless as soon as \( Cu^{2+} \) ions are finished.
(c) Lead bromide dissociate into ions in the molten state whereas it does not dissociate in solid state. The ions become free when lead bromide is in molten state but in the solid state the ions are not free since they are packed tightly together due to electrostatic force between them.
(d) Aluminium has great affinity towards oxygen, so it is not reduced by reducing agent. Therefore it is extracted from its oxide by electrolytic reduction.
(e) As per electrolytic reactions, 4\( H^+ \) are needed at cathode and 4\( OH^- \) at the anode and two molecules of water are produced at the anode. Hence for every two molecules of water, two molecules of hydrogen and one molecule of oxygen are liberated at the cathode and anode respectively. 2\( H_2O \rightarrow 2H_2 \) [cathode] + \( O_2 \) [anode]
(f) This is because \( HNO_3 \) is volatile.
(g) Ammonia is a covalent compound. Therefore, it is unionized in the gaseous state but in the aqueous solution it gives \( NH_4OH \) which is a weak electrolyte and dissociates into ions.
(h) Graphite is unaffected by the bromine vapours.
(i) Silver nitrate is not used as electrolyte for electroplating with silver because the deposition of silver will be very fast and hence not very smooth and uniform.
(j) Carbon tetrachloride is a liquid and does not conduct electricity because it is a covalent compound and there are no free ions present and contain only molecules.
In simple words: Different substances behave differently during electrolysis based on their chemical structure — some conduct electricity only when molten, others need water to form ions, and some never conduct at all.

📝 Teacher's Note: For part (e), use the water electrolysis equation to show the 2:1 ratio mathematically. Students often forget that the ratio refers to volumes, not molecules. Demonstrate with actual gas collection if possible.

🎯 Exam Tip: For redox questions, always mention both oxidation (loss of electrons) and reduction (gain of electrons) happening simultaneously. For conducting vs non-conducting, focus on presence or absence of free mobile ions.

Question 2. Classify the following substance 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 electrolyte: Dilute hydrochloric acid, dilute sulphuric acid, ammonium chloride, sodium acetate
(b) Weak electrolyte: Acetic acid, ammonium hydroxide
(c) Non-electrolyte: Carbon tetrachloride
In simple words: Strong electrolytes completely break into ions in solution, weak electrolytes only partially break into ions, and non-electrolytes don't form ions at all.

📝 Teacher's Note: Explain that salts are generally strong electrolytes, strong acids and bases are strong electrolytes, weak acids and bases are weak electrolytes, and covalent compounds like carbon tetrachloride are non-electrolytes.

🎯 Exam Tip: Remember that "dilute" doesn't mean "weak" — dilute HCl is still a strong electrolyte because it ionizes completely, there's just less of it in solution.

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.
Answer: (a) Molecules
(b) Will not
In simple words: Pure water contains only water molecules, no ions, so it cannot conduct electricity like a metal wire would.

📝 Teacher's Note: Emphasize the word "pure" — tap water conducts electricity because of dissolved salts, but pure distilled water does not. This is why we can safely handle pure water around electronics.

🎯 Exam Tip: Don't confuse "pure water" with "tap water" or "sea water" — only pure water is non-conducting. Always read the question carefully for such qualifiers.

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?
Answer: 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 \( SO_4^{2-} \) ions and help in dissociating water into \( H^+ \) and \( OH^- \), water being a polar solvent.
In simple words: Adding sulphuric acid creates ions in the water, which act like tiny carriers that allow electric current to flow through the solution.

📝 Teacher's Note: Draw the process step by step: pure water → add H₂SO₄ → H⁺ and SO₄²⁻ ions form → these ions make the solution conductive → now electrolysis can happen. The acid doesn't get used up, it just enables conduction.

🎯 Exam Tip: Mention that we add only a small amount of acid — its main purpose is to provide ions for conduction, not to participate in the main reaction. The water molecules are what actually get decomposed.

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

Answer: The completed table shows the missing entries: For silver plating - Anode: Plate of pure silver, Cathode: Article to be electroplated. For copper purification - Anode: Impure copper, Cathode: Thin strip of pure copper.
In simple words: In electroplating, pure metal goes on the positive side and the object being coated goes on the negative side. In purification, impure metal goes on positive side and gets purified on the negative side.

📝 Teacher's Note: Help students remember that in electroplating, the metal always travels from anode to cathode. Draw arrows showing metal ions moving through the solution. For purification, impurities fall off as sludge.

🎯 Exam Tip: In both applications, the cathode receives the pure metal. The key difference is that in plating we coat an object, in purification we start with impure metal and get pure metal.

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.
Answer: Electricity, Chemical
In simple words: Electrolysis means passing electric current through a liquid, which breaks down the liquid into different substances — this is a chemical change, not just physical.

📝 Teacher's Note: Emphasize that electrolysis always involves breaking or forming chemical bonds — new substances are formed. This distinguishes it from just heating or cooling, which are physical changes.

🎯 Exam Tip: Remember the definition exactly — "passage of electricity through a liquid accompanied by chemical change." Both parts are essential for full marks.

Question 2004. Element X is a 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.
Answer: (a) \( X \rightarrow X^{2+} + 2e^- \), \( Y + 3e^- \rightarrow Y^{3-} \)
(b) \( Y_2 + 3X \rightarrow X_3Y_2 \)
(c) (i) It is used for the electroplating of metals. (ii) It is also used in purification of metals.
(d) Cathode, Anode
In simple words: Metals lose electrons to form positive ions, non-metals gain electrons to form negative ions. During electrolysis, positive ions go to the negative electrode and negative ions go to the positive electrode.

📝 Teacher's Note: Use the valency to determine the charges — valency 2 means X forms X²⁺, valency 3 means Y forms Y³⁻. For the compound formula, cross multiply the charges to get X₃Y₂.

🎯 Exam Tip: In electrolysis questions about anode mass decreasing, think of electroplating and purification — the anode metal dissolves into the solution, reducing its mass.

Question 2004(2).
(a) What kind of particles will be found in a liquid compound which is a non – electrolyte?
(b) If HX is a weak acid, what particles will be present in its dilute solution apart from those of water?
Answer: (a) Only molecules will be present in a non-electrolyte liquid compound, as it does not dissociate into ions.
(b) In a dilute solution of weak acid HX, the particles present apart from water molecules will be: HX molecules (mostly undissociated), \( H^+ \) ions, and \( X^- \) ions (in small amounts due to partial dissociation).
In simple words: Non-electrolytes don't break apart into ions, they stay as complete molecules. Weak acids only partially break apart, so you have both whole acid molecules and some ions.

📝 Teacher's Note: Contrast this with strong acids which completely ionize. For weak acids, draw an equilibrium showing HX ⇌ H⁺ + X⁻ with the equilibrium lying mostly to the left (more molecules than ions).

🎯 Exam Tip: For weak electrolytes, always mention that both the molecular form and the ionic forms are present simultaneously due to partial dissociation.

Question. Cations 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).
Answer: Cations are formed by loss of electrons and anions are formed by gain of electrons.
In simple words: When atoms lose electrons, they become positively charged (cations). When atoms gain electrons, they become negatively charged (anions).

📝 Teacher's Note: Use the memory device "PANIC" - Positive charges (cations) lose electrons, Negative charges (anions) gain electrons. Draw simple diagrams showing electron transfer.

🎯 Exam Tip: Remember that losing electrons makes atoms positive (like losing money makes you poorer), gaining electrons makes atoms negative.

Question. What ions must be present in a solution used for electroplating a particular metal?
Answer: The electrolyte used for the purpose must contain the ions of metal which is to be electroplated on the article.
In simple words: If you want to coat something with copper, your solution must have copper ions in it. The metal ions get deposited on the object during electroplating.

📝 Teacher's Note: Use practical examples like silver plating jewelry or chrome plating car parts. Students understand better when they see real-world applications.

🎯 Exam Tip: Always mention that the electrolyte must contain ions of the same metal that is being plated - this is the key point examiners look for.

Question. Explain how electrolysis is an example of redox reaction.
Answer: 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. Example: Dissociation of sodium chloride during electrolysis.
\( \text{NaCl} \rightleftharpoons \text{Na}^+ + \text{Cl}^- \)
At cathode: \( \text{Na}^+ + e^- \rightarrow \text{Na} \) (Reduction)
At anode: \( \text{Cl}^- - e^- \rightarrow \text{Cl} \) (Oxidation)
\( \text{Cl} + \text{Cl} \rightarrow \text{Cl}_2 \)
Overall reaction: \( 2\text{NaCl} \rightarrow 2\text{Na} + \text{Cl}_2 \)
In simple words: During electrolysis, reduction happens at the cathode (ions gain electrons) and oxidation happens at the anode (ions lose electrons), making it a redox reaction.

📝 Teacher's Note: Emphasize the memory device "RED CAT" (Reduction at Cathode) and "AN OX" (Anode Oxidation). Show both half-reactions separately before combining.

🎯 Exam Tip: Always write both the cathode and anode reactions separately, then the overall reaction. Mention the words "reduction" and "oxidation" explicitly.

Question. Explain why Cu, though a good conductor of electricity is a non electrolyte.
Answer: Because Copper is an electronic conductor as it is a metal.
In simple words: Copper conducts electricity through moving electrons (like water through pipes), not through moving ions. Electrolytes conduct through ion movement.

📝 Teacher's Note: Draw diagrams showing electron flow in metals vs ion movement in electrolytes. Use the analogy of different types of traffic - cars on roads vs people walking.

🎯 Exam Tip: Clearly distinguish between electronic conduction (metals) and ionic conduction (electrolytes). This difference is crucial for full marks.

Question. Solid sodium chloride does not allow electricity to pass through?
Answer: In solid sodium chloride, \( \text{Na}^+ \) and \( \text{Cl}^- \) 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 applied. Hence no current.
In simple words: In solid salt, the positive and negative ions are stuck tightly together like magnets. They cannot move freely to carry electric current.

📝 Teacher's Note: Use the analogy of people in a crowded room vs people in an open field. In solids, ions are "stuck" but in solutions, they can move freely.

🎯 Exam Tip: Mention both "strong electrostatic forces" and "ions cannot move freely" for complete answer. Movement of ions is essential for conduction.

Question. Name the gas released at cathode when acidulated water is electrolyzed.
Answer: Hydrogen gas is released at cathode when acidulated water is electrolyzed.
In simple words: When we pass electricity through acidified water, hydrogen gas bubbles form at the negative electrode (cathode).

📝 Teacher's Note: Demonstrate this with a simple electrolysis setup. Students can see the gas bubbles forming and test for hydrogen with a glowing splint.

🎯 Exam Tip: Remember that at cathode, hydrogen is released; at anode, oxygen is released during water electrolysis. The ratio is 2:1.

Question. Copper sulphate solution is electrolyzed using a platinum anode. Give the name of the electrodes A and B.
Answer: The name of electrode A is Platinum anode and that of electrode B is platinum or copper cathode.
In simple words: Electrode A (positive terminal) is the platinum anode, and electrode B (negative terminal) is the cathode which can be made of platinum or copper.

📝 Teacher's Note: Show actual electrodes and explain that the anode material affects what gets oxidized, while cathode material can be inert or reactive.

🎯 Exam Tip: Always specify the material and type (anode/cathode) when naming electrodes in electrolysis questions.

Question. Which electrode is the oxidizing electrode?
Answer: Anode acts as oxidizing electrode.
In simple words: The anode is where oxidation happens - substances lose electrons here, so it's called the oxidizing electrode.

📝 Teacher's Note: Connect this to the mnemonic "AN OX" (Anode Oxidation). Emphasize that the anode causes other substances to get oxidized.

🎯 Exam Tip: Remember that anode = oxidation = oxidizing electrode. This is a direct relationship that appears frequently in exams.

Question. A strip of copper is placed in four different colourless salt solutions. They are \( \text{KNO}_3 \), \( \text{AgNO}_3 \), \( \text{Zn(NO}_3)_2 \), \( \text{Ca(NO}_3)_2 \). Which one of the solutions will finally turn blue?
Answer: \( \text{AgNO}_3 \) solution will turn blue.
In simple words: When copper reacts with silver nitrate, copper goes into solution as blue copper ions while silver metal gets deposited on the copper strip.

📝 Teacher's Note: Explain the reactivity series - copper can displace silver but not zinc, potassium, or calcium. The blue color comes from \( \text{Cu}^{2+} \) ions.

🎯 Exam Tip: Look at the reactivity series - copper can only displace metals below it. Blue color always indicates presence of \( \text{Cu}^{2+} \) ions.

Question. Choose A, B, C or D to match the descriptions 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 aluminium 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.
Answer:
(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 dissociation of solute molecules: C. Weak electrolyte
(v) A sugar solution with sugar molecules and water molecules: A. Non-electrolyte
In simple words: Molten salts conduct very well (strong), metals conduct through electrons, partial ionization means weak conduction, and molecular compounds like sugar don't conduct at all.

📝 Teacher's Note: Create a classification chart showing examples of each type. Use everyday examples like table salt (strong), vinegar (weak), and sugar water (non-electrolyte).

🎯 Exam Tip: Remember the key indicators: complete ionization = strong, partial ionization = weak, no ionization = non-electrolyte, metals = electronic conduction.

Question. Here is an electrode reaction: \( \text{Cu} \rightarrow \text{Cu}^{2+} + 2e^- \). At which electrode (anode or cathode) would such a reaction take place? Is this an example of oxidation or reduction?
Answer: The reaction takes place at anode. This is an example of oxidation.
In simple words: When copper loses electrons to form copper ions, it's oxidation, which always happens at the anode (positive electrode).

📝 Teacher's Note: Emphasize that loss of electrons = oxidation = anode. Use "LEO the lion says GER" - Lose Electrons Oxidation, Gain Electrons Reduction.

🎯 Exam Tip: Look at the equation direction - if electrons are being lost (products side), it's oxidation at anode. If gained (reactants side), it's reduction at cathode.

Question. A solution contains magnesium ions (\( \text{Mg}^{2+} \)), iron (II) ions (\( \text{Fe}^{2+} \)) and copper ions (\( \text{Cu}^{2+} \)). 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.
Answer: \( \text{Cu}^{2+} \) will discharge easily at cathode. Reaction at cathode: \( \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \)
In simple words: Copper ions get reduced first because copper is the least reactive metal among the three, so it gets deposited first at the cathode.

📝 Teacher's Note: Teach the order of discharge - less reactive metals get discharged first. Use the reactivity series: Mg > Fe > Cu, so Cu discharges first.

🎯 Exam Tip: Always refer to reactivity series for order of discharge. Less reactive metals discharge first at cathode, more reactive non-metals discharge first at anode.

Question. Why is carbon tetrachloride, which is a liquid, a non-electrolyte?
Answer: Carbon tetrachloride is a non-electrolyte because it is a covalent compound. It does not ionize and hence does not conduct electricity.
In simple words: Carbon tetrachloride molecules stick together as whole units - they don't break into ions, so there are no charged particles to carry electric current.

📝 Teacher's Note: Contrast ionic compounds (which break into ions) with covalent compounds (which remain as molecules). Use ball-and-stick models if available.

🎯 Exam Tip: For covalent compounds, always mention "does not ionize" and "no free ions" as the reason for non-conduction. Being liquid doesn't automatically mean it conducts.

Question. 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.
Answer: (d) Lead is deposited at the cathode
In simple words: During electrolysis, metal ions (lead) always go to the negative electrode (cathode) where they gain electrons and get deposited as metal.

📝 Teacher's Note: Reinforce that metals always deposit at cathode, non-metals at anode. Lead ions are positive, so they go to negative cathode.

🎯 Exam Tip: Remember: positive ions → negative electrode (cathode), negative ions → positive electrode (anode). Lead is a metal, so it deposits at cathode.