Chapter 11: Chemical Effects Of Electric Current 

1. Name a solid material that conducts electricity.

Copper wire, Iron nail. (Any metal).(Copper ka taar, Lohe ki keel).

2. Name a solid material that is an insulator.

Rubber, Plastic, Wood.(Rubber, Plastic, Lakdi).

3. Does distilled water conduct electricity?

No, it is a poor conductor/insulator.(Nahi, yeh heen chalak/kuchalak hai).

4. Does tap water conduct electricity? Why?

Yes, because it contains dissolved salts/minerals (ions).(Haan, kyunki ismein ghule hue namak/khanij (ions) hote hain).

5. Name a device used to detect weak currents.

LED or Magnetic Compass.(LED ya Chumbakiy Sui).

6. What are charged particles responsible for conduction in liquids called?

Ions.(Ions).

7. What is the chemical effect of electric current?

Passing current through a conducting liquid causes chemical reactions.(Conducting liquid se current guzarne par chemical reaction hona).

8. What is electrolysis?

Decomposition of an electrolyte by passing electric current.(Electric current se electrolyte ka tootna).

9. What is an electrode?

Metal rod/plate through which current enters/leaves electrolyte.(Dhatu ki chhad/plate jisse current electrolyte mein aata/jaata hai).

10. What is the positive electrode called?

Anode.(Anode).

11. What is the negative electrode called?

Cathode.(Cathode).

12. Name one effect observed during electrolysis of water.

Gas bubbles formed (H₂ at cathode, O₂ at anode).(Gas ke bulbule banna).

13. What is electroplating?

Depositing a layer of desired metal onto another material using electrolysis.(Electrolysis se ek dhatu ki parat dusre par jamana).

14. In electroplating, the object to be coated is made the:

Cathode (negative electrode).

15. Give one reason why electroplating is done.

For appearance (shininess) or Protection (from rust).(Sundarta ya Suraksha (jung se)).

16. Which metal is often plated on car parts for a shiny look?

Chromium.(Chromium).

17. Coating iron with zinc is called:

Galvanisation.(Galvanisation).

1. Explain why tap water conducts electricity whereas distilled water does not.

• Conductivity in liquids depends on presence of mobile ions.(Liquids mein conductivity mobile ions par nirbhar karti hai).
• Tap water contains dissolved salts and minerals which dissociate into ions when dissolved.(Nal ke paani mein ghule hue salts/minerals hote hain jo ions banate hain).
• These ions carry electric charge, allowing tap water to conduct electricity.
• Distilled water is pure water (H₂O) with almost no dissolved salts. It has very few ions. (Distilled water shuddh paani hai, usmein lagbhag koi salt nahi hota. Bahut kam ions hote hain).
• Therefore, distilled water is a poor conductor of electricity.

2. To test conductivity of a liquid, the bulb in the tester doesn’t glow. What could be the reasons and what can be done?

• Reason 1: The liquid might be an insulator or poor conductor (like distilled water, sugar solution).(Liquid insulator ho sakta hai).
• Reason 2: The current flowing through the liquid might be too weak to make the bulb filament glow. (Current bulb jalane ke liye bahut kamzor ho sakta hai).
• What to do:
  • Replace the bulb with an LED (Light Emitting Diode), which glows even on weak current.(Bulb ki jagah LED istemal karein).
  • Use a magnetic compass 🧭; even weak current produces magnetic effect causing needle deflection.(Magnetic compass istemal karein; kamzor current se bhi sui hilegi).

3. What are the common chemical effects when electric current passes through a conducting solution?

• Formation of gas bubbles 💨 at the electrodes (e.g., H₂/O₂ from water).
• Deposition of metal 🪙 on the cathode (negative electrode).
• Change in colour 🎨 of the solution due to chemical reaction.
• Dissolving of metal from the anode (positive electrode) into the solution.

4. Describe the process of electroplating copper onto an iron key.

• Setup: Iron key is cleaned and made the Cathode (-ve). A pure copper plate is made the Anode (+ve). The electrolyte is Copper Sulphate (CuSO₄) solution. (Lohe ki chabi ko Cathode, Copper plate ko Anode, aur Copper Sulphate solution ko electrolyte banate hain).
• Process: When current passes: CuSO₄ dissociates into Cu²⁺ and SO₄²⁻ ions.
• Cu²⁺ ions (positive) move towards the Cathode (key).
• At the cathode, Cu²⁺ ions gain electrons and deposit as pure Copper metal layer onto the key ✨🔑.
• From the Anode (copper plate), an equal amount of copper dissolves into the solution as Cu²⁺ ions, replenishing the ions lost during deposition.

5. List three uses or applications of electroplating.

• Appearance ✨: Coating less expensive metals with gold/silver for jewellery. Chromium plating for shiny look on taps/car parts.
• Protection from Corrosion 🛡️: Coating iron with Zinc (galvanisation) or Chromium to prevent rusting. Coating food cans with Tin.
• Durability/Hardness: Plating objects with hard metals like chromium makes them scratch resistant.
• (Also: Used in electronics for coating connectors).

6. Why should we not handle electrical appliances with wet hands or while standing on a wet floor?

• Our body is a conductor, but normally resistance is high.
• Tap water (or water with impurities/sweat) is a good conductor of electricity due to dissolved salts (ions).(Nal ka paani/paseena bijli ka achha suchalak hai).
• Wet hands or standing on a wet floor provides an easy path for electric current to flow through our body to the earth if we touch a faulty appliance.(Geele haath ya farsh se current hamare sharir se aasani se zameen tak ja sakta hai).
• This can result in a severe electric shock ⚡💀, which can be very dangerous or fatal.(Isse zor ka bijli ka jhatka lag sakta hai, jo khatarnaak ho sakta hai).

7. What is an LED? Why is it often preferred over a bulb in testers?

• LED: Light Emitting Diode.🌟
• It’s a type of semiconductor diode that emits light when current passes through it.
• Why Preferred?:
  • LEDs can glow even when a very weak electric current flows through them.(LED bahut kamzor current par bhi jal sakti hai).
  • Ordinary bulbs require a relatively stronger current to heat up the filament enough to glow.(Saadharan bulb ko jalne ke liye zyada current chahiye).
  • Therefore, LEDs are better for testing the conductivity of liquids that might be poor conductors (allowing only weak current).
• LEDs have two terminals (leads); current flows only in one direction (+ to -).

8. Name three liquids which conduct electricity and three which do not.

• Conducting Liquids ✅:
  • Tap Water 🚰
  • Lemon Juice 🍋 (Acid solution)
  • Salt Solution 🧂 (e.g., Copper Sulphate)
  • Vinegar (Acetic acid solution)
• Non-Conducting (Poor Conductor/Insulator) Liquids ❌:
  • Distilled Water
  • Sugar Solution
  • Kerosene/Oil 🛢️
  • Alcohol
  • Honey 🍯

9. What happens when electric current is passed through copper sulphate solution using copper electrodes?

• Copper sulphate (CuSO₄) dissociates into Copper ions (Cu²⁺) and Sulphate ions (SO₄²⁻).
• Cu²⁺ ions move towards the negative electrode (Cathode).
• At Cathode: Cu²⁺ ions gain electrons and deposit as pure Copper metal (Cu) onto the cathode. Cathode becomes thicker.
• At Anode: Copper atoms from the copper anode lose electrons and dissolve into the solution as Cu²⁺ ions. Anode becomes thinner.
• The concentration of CuSO₄ in the solution remains roughly constant during the process. This is used in copper refining and electroplating.

10. What is galvanisation? Why is it done?

• Galvanisation is the process of depositing a layer of Zinc metal onto Iron objects.(Lohe ki vastuon par Zinc dhatu ki parat jamana).
• It is a type of electroplating (or sometimes done by dipping iron in molten zinc).
• Why done?: Zinc is more reactive than Iron but forms a protective oxide layer. This zinc layer prevents the underlying Iron from coming into contact with air and moisture.(Zinc layer Iron ko hawa/nami ke sampark mein aane se rokta hai).
• This protects the Iron object from rusting 🔗🛡️.(Isse lohe ki vastu jung lagne se bachti hai).
• Example: Galvanised Iron (GI) pipes used for water supply.

11. Write any two harmful chemical effects of electric current if not handled properly.

• Electric Shock ⚡💀: Passing current through human body (a conductor, especially when wet) can cause severe shock, burns, muscle contraction, or even death. (Insani sharir se current guzarne par zor ka jhatka, jalna, ya maut ho sakti hai).
• Fires 🔥: Short circuits or overloading can cause excessive heat due to electric current, leading to fires in wiring or appliances. (Short circuit ya overload se current zyada garmi paida karke aag laga sakta hai).
• (Also potentially harmful decomposition products during electrolysis of certain substances, but shock/fire are more direct dangers).

1. Explain with an experiment how we can test whether a liquid conducts electricity or not, using a bulb or LED.

Aim:

Materials Required:

Procedure:

1. Make a simple tester circuit: Connect one terminal of the battery to one terminal of the bulb/LED using a wire. Connect the other terminal of the bulb/LED to one free end of another wire. Connect the other terminal of the battery to the free end of a third wire.
(Ek simple tester circuit banayein: Battery ke ek terminal ko wire se bulb/LED ke ek terminal se jodein. Bulb/LED ke dusre terminal ko ek aur wire ke free end se jodein. Battery ke dusre terminal ko teesre wire ke free end se jodein).
2. Clean the two free ends of the wires thoroughly (remove insulation if needed, sandpaper helps).
3. Pour the liquid to be tested into the clean, dry beaker.
4. Dip the two free ends of the tester wires into the liquid, ensuring they do not touch each other, but are reasonably close (e.g., 1 cm apart).
(Tester wires ke dono free ends ko liquid mein duboye, dhyaan rahe ki ve ek doosre ko na chhuein, lekin kareeb hon).
5. Observe if the bulb/LED glows.

Observation & Conclusion:

• If Bulb/LED glows 💡: It means the circuit is complete, and the liquid allowed current to pass. The liquid is a **conductor** of electricity. Example: Lemon juice, tap water, salt solution.
• If Bulb/LED does not glow: It means the circuit is incomplete, and the liquid did not allow current to pass (or the current was extremely weak). The liquid is a **poor conductor (insulator)**. Example: Distilled water, sugar solution, oil.
• Note: If bulb doesn’t glow, repeating with an LED is advisable as it detects weaker currents.

Precautions:

• Use a low voltage battery (like from a torch).
• Do not test liquids connected to household mains supply!
• Clean wire ends properly.

2. What are chemical effects of electric current? Describe an activity to show one such effect, like deposition of metal.

Chemical Effect: Passing electric current through a conducting liquid (electrolyte) causes chemical reactions, like decomposition or deposition. This phenomenon is called the chemical effect of current.

Activity: To Show Deposition of Copper

• Materials: Beaker, Copper Sulphate (CuSO₄) solution, Two copper plates (approx. 10cm x 4cm), Battery 🔋, Connecting wires.
• Procedure:
  1. Dissolve about two teaspoons of copper sulphate in 250mL distilled water in a clean beaker. Add a few drops of dilute sulphuric acid to make it more conducting.
  2. Clean the copper plates with sandpaper, rinse with water, and dry them.
  3. Connect the copper plates to the terminals of a battery using connecting wires.
  4. Immerse the plates in the copper sulphate solution, ensuring they don’t touch.
  5. Allow current to pass for about 15-20 minutes.
  6. Observe the plates carefully after removing them.
• Observation: You will notice a layer of reddish-brown copper deposited on the copper plate connected to the **negative terminal (Cathode)**. The copper plate connected to the **positive terminal (Anode)** might become slightly thinner. ✨➡️➖
• Explanation: CuSO₄ dissociates into Cu²⁺ and SO₄²⁻ ions. Cu²⁺ (positive ions) move to the negative cathode, gain electrons, and deposit as copper metal. Copper from the positive anode dissolves into the solution as Cu²⁺ ions, replenishing those deposited. This shows deposition of metal, a chemical effect.

3. What is electroplating? Explain the process with the help of an example like plating an iron object with chromium.

Electroplating: Depositing a thin layer of a desired metal onto another material using electrolysis.

Purpose:

Process (Example: Chromium Plating on Iron):

• Setup:
  • Clean the Iron object thoroughly. Make it the **Cathode** (-ve terminal).
  • Use a plate/rod of pure **Chromium** metal as the **Anode** (+ve terminal).
  • Use a solution containing Chromium salt (e.g., Chromic acid solution) as the **Electrolyte**.
• Mechanism:
  • When current passes, electrolyte provides Chromium ions (Cr³⁺).
  • Positive Cr³⁺ ions are attracted towards the negative Cathode (Iron object).
  • At the Cathode, Cr³⁺ ions gain electrons and deposit as a thin, shiny layer of Chromium metal on the Iron object.
  • Chromium metal from the Anode dissolves into the solution to replace the deposited ions.
• The result is an iron object coated with a bright, hard, scratch-resistant, and corrosion-resistant layer of chromium.

4. Differentiate between conductors and insulators, giving examples of solids and liquids for each.

Materials are classified based on their ability to conduct electricity:

Conductors (Suchalak) ✅⚡:

• Materials that allow electric current to pass through them easily.
• They have free electrons (in solids) or mobile ions (in liquids) that can carry charge.
• Solid Examples: Metals like Copper (Cu), Aluminium (Al), Iron (Fe), Silver (Ag – best conductor). Graphite (a form of Carbon) is also a conductor.
• Liquid Examples: Tap water, Salt water, Lemon juice (acids), Soap solution (bases), Copper sulphate solution (salt solutions).

Insulators (Kuchalak / Poor Conductors) ❌⚡:

• Materials that do NOT allow electric current to pass through them easily (or at all).
• They lack free electrons or mobile ions to carry charge.
• Solid Examples: Rubber, Plastic, Wood, Glass, Cotton 솜, Pure Mica.
• Liquid Examples: Distilled water, Sugar solution, Alcohol, Kerosene, Vegetable oil 🛢️, Honey 🍯.

5. Describe an activity to show that lemon juice or vinegar conducts electricity.

Aim:

Materials:

Procedure:

1. Set up the tester circuit: Battery connected to LED, LED to one free wire, other battery terminal to another free wire.
2. Ensure the LED lights up when the free wire ends are touched together briefly (circuit works).
3. Pour some lemon juice (or vinegar) into the clean beaker.
4. Clean the free ends of the tester wires.
5. Dip the wire ends into the lemon juice/vinegar, keeping them apart but close.
6. Observe the LED.

Observation:

Conclusion:

Reason: Lemon juice (citric acid) and vinegar (acetic acid) are acids. Acids dissociate in water to produce mobile ions (H⁺ ions etc.) which conduct electricity.

6. List some common applications of electroplating in daily life and state the purpose for each.

Electroplating Uses:

• Chromium Plating ✨🛡️:
  • Done on bath taps 🚿, car bumpers, bicycle handlebars, kitchen gas burners.
  • Purpose: Gives a shiny appearance, resists scratches, prevents corrosion (rusting).
• Gold/Silver Plating 💍💰:
  • Done on less expensive metals (like brass, copper) to make jewellery.
  • Purpose: Makes ornaments look attractive like real gold/silver at a lower cost.
• Tin Plating 🥫:
  • Iron cans used for storing food are coated with Tin.
  • Purpose: Tin is less reactive than iron, so it prevents food from coming into contact with iron and getting spoiled/corroded.
• Zinc Plating (Galvanisation) 🔗🛡️:
  • Coating Iron objects (like bridges, automobile bodies, pipes) with Zinc.
  • Purpose: Protects iron from rusting, as zinc forms a protective layer.
• Copper Plating:
  • Used in electrical components, sometimes as a base layer for other plating.
  • Purpose: Improve conductivity, corrosion resistance, base for further plating.

7. Explain why an LED is used in a tester instead of an electric bulb when testing liquids which may be poor conductors.

• Electric current causes a heating effect. An ordinary electric bulb glows only when its filament gets heated to a high temperature by the current passing through it. (Saadharan bulb tabhi jalta hai jab uska filament current se bahut garam ho jaata hai).
• If the current flowing through the circuit (and the liquid) is weak, it may not be sufficient to heat the filament enough to make it glow, even though the liquid might be conducting slightly. (Agar current kamzor hai, toh filament shayad itna garam na ho paye ki bulb jale, bhale hi liquid thoda conduct kar raha ho).
• An LED (Light Emitting Diode) works on a different principle (related to semiconductors) and requires very little current to glow 🌟. (LED alag siddhant par kaam karta hai aur bahut kam current par bhi jal jaata hai).
• Therefore, an LED can detect even weak currents that might pass through poor conducting liquids (like tap water with low salt content, or very dilute acid/base solutions), which an ordinary bulb might fail to detect. (Isliye, LED kamzor conductors se guzarne wale kamzor current ka bhi pata laga sakta hai, jise saadharan bulb miss kar sakta hai).
• This makes LED testers more sensitive for checking the conductivity of various liquids.

8. During electrolysis of water (acidified), what gases are produced and at which electrodes?

When electric current is passed through water (with a few drops of acid like sulphuric acid added to make it conducting), water (H₂O) decomposes.

• The process is called Electrolysis of Water.
• At the Cathode (-ve electrode): Bubbles of Hydrogen gas (H₂) are produced 💨. (Water breaks down, H⁺ ions gain electrons: 2H⁺ + 2e⁻ → H₂)
• At the Anode (+ve electrode): Bubbles of Oxygen gas (O₂) are produced 💨. (Water breaks down, hydroxide ions/water molecules lose electrons: 2H₂O → O₂ + 4H⁺ + 4e⁻)
• The volume of hydrogen gas produced is typically twice the volume of oxygen gas produced (because water molecule has H₂O ratio). 📊 H₂ : O₂ = 2 : 1

9. List some precautions to be taken while handling electrical circuits or appliances, especially concerning water.

• Never touch electrical switches or appliances with wet hands 🚫💧🖐️. Water (especially impure/tap water) makes our hands conducting, increasing the risk of electric shock. (Geele haathon se switch/appliance na chhuein).
• Never operate electrical appliances while standing on a wet floor or in water. This provides an easy path for current to flow through the body to the ground. (Geele farsh par khade hokar appliance na chalayein).
• Never use water to extinguish an electrical fire 🚫💧🔥⚡. Use a CO₂ fire extinguisher or sand. (Bijli ki aag bujhane ke liye paani istemal na karein).
• Keep electrical appliances away from water sources (like sinks, bathrooms) unless they are specifically designed for wet conditions.
• Never insert fingers or metal objects into electrical sockets.
• Use proper wiring and insulation. Replace frayed or damaged wires immediately. (Sahi wiring aur insulation ka istemal karein. Kharab taaron ko turant badlein).
• Use testers with low voltage cells/batteries for experiments, never connect directly to mains.

10. Besides electroplating, name and briefly describe another application of the chemical effect of electric current.

Another important application is the Purification or Refining of Metals, especially Copper.

Refining of Copper (Example):

• Setup:
  • A thick block of **impure copper** metal is made the **Anode** (+ve). (Ashuddh Copper ka mota block Anode banaya jaata hai).
  • A thin strip of **pure copper** metal is made the **Cathode** (-ve). (Shuddh Copper ki patli patti Cathode banayi jaati hai).
  • The **Electrolyte** is a solution of Copper Sulphate (CuSO₄) acidified slightly.
• Process:
  • When current passes, pure copper from the impure anode dissolves into the electrolyte as Cu²⁺ ions. (Current guzarne par, Anode (ashuddh copper) se shuddh copper Cu²⁺ ions ke roop mein electrolyte mein ghulta hai).
  • An equivalent amount of pure Cu²⁺ ions from the electrolyte gets deposited onto the pure copper cathode. (Electrolyte se utna hi shuddh Cu²⁺ ion Cathode (shuddh copper) par jama ho jaata hai).
  • The impurities from the anode either remain dissolved in the solution or settle down below the anode as **’Anode Mud’**. (Anode ki ashuddhiyan ya toh solution mein ghul jaati hain ya Anode ke neeche ‘Anode Mud’ ke roop mein jama ho jaati hain).
• Result: Pure copper gets transferred from the impure anode to the pure cathode, leaving impurities behind. This process yields very high purity copper. ✨