Untitled Flashcards Set

CHEMICAL EFFECTS OF ELECTRIC CURRENT

CLASS TASK 1

Q1- Differentiate between conductors and Insulators.

Answer-

Q2-Do liquids conduct electricity?

Answer- There are many liquids that conducts electricity. They are called ELECTROLYTES. All acids, bases and salts are good electrolytes. In liquids electricity is conducted by charged particles called ions (negatively or positively charged atoms).

The liquids that do not conduct electricity are called NON-ELECTROLYTES. EX. Distilled water, Sugar solution, Kerosene.

Q3- Why it is not safe to touch electrical appliances with wet hands?

Answer-Tap water is a good conductor because the dissolved salts in the tap water increases the conductivity of water. So when we touch electrical appliances with wet hands the current easily passes through it and gives an electric shock. Hence it is not safe to touch electrical appliances with wet hands.

Q4- Write an activity to check various liquids for conduction of electricity.

AIM-  To check various liquids for conduction of electricity.

Material required- Battery and battery holder, copper strips.LED bulb.

Procedure- Set up a simple circuit using  battery, a bulb or LED, and two copper strips connected to electric wires. Place different liquids like distilled water, saltwater, sugar water, and tap water in separate beakers. Dip the strips into each liquid one by one.

Observation- The liquid in which bulb lights up is the good conductor of electricity while the liquids in which bulb did not glow are poor conductors of electricity.

Conclusion- The liquids like Salt solution, tap water or any acid or base are the good conductors of electricity while distilled water and sugar solution are poor conductors.

CLASS TASK 2

Q1 How does something become charged?

Answer- An atom is the smallest unit of matter. It contains neutrons ( no charge), protons( +)  and electrons( -). In an atom, the number of electrons is equal to the number of protons hence an ATOM HAS NO CHARGE , IT IS ELECTRICALLY NEUTRAL. As electrons are revolving around the nucleus in an atom some of the elements tend to lose or gain electrons and develop charge to form ions (Charged atom).

Q2- Explain the following terms.

Electrolysis :– A process in which a substance in a liquid state gets decomposed into its constituent ions on passage of electric current.

Electrolyte :– A liquid which gets dissociated into ions and  conducts electricity is called an electrolyte. The liquid which does not get dissociated is called Non-Electrolyte.

Electrodes : – The rods, plates or wiresof good conductors that are partially immersed in the solution during electrolysis are called electrodes. Ex. copper or graphite.

Anode :– The electrode that is connected to the positive terminal of a battery is called anode. Anions-  Negative charge ions that move (attracted) towards anode (+ve terminal).

Cathode :- The electrode that is connected to the negative terminal of battery  is called cathode.

Cations-  Positively  charged ions that move  (attracted) towards cathode (-ve terminal).

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Q3- Write an activity to show Electrolysis of water with the help of a diagram. Give Chemical equation.

AIM : To show electrolysis of water
Materials Required : A Beaker, two sharpened pencils, water, a battery and a switch

PROCEDURE : i) Take water in a glass tumbler. Add a few drops of acid in it to make it conducting.

ii) Take two pencils sharpened from both the ends that will act as electrodes.

iii)Fix them with the help of a cardboard.

iv) Connect the circuit as shown in the figure.
v) Turn on the switch.
OBSERVATION : When current is passed through acidulated water, it gets dissociated into hydrogen and oxygen ions. It is observed that Hydrogen bubbles get deposited at  the cathode and Oxygen bubbles get deposited at  the anode.

CONCLUSION : The chemical change is due to electrolysis of water, in which water gets decomposed into hydrogen and oxygen. First, water splits into hydrogen (H⁺) and hydroxide (OH^–) ions. These lose charge to form hydrogen and oxygen gas at the electrodes.

The following changes take place during electrolysis of water.

H2O   →   H+ + OH-

At cathode: 2H+ + 2e-   →  H2 

At anode: 4OH- - 4e-→  O2 + 2H2O

Overall reaction –2H2O   →  2H2 + O2

CLASS TASK 3

Q1- Give few uses of electrolysis.

ANSWER-

Q2- Explain catalytic refining of copper.

Answer- It is the process of getting pure copper from its mixed state ( pure copper) based on the principle of electrolysis.

1. In the electrolytic refining of copper, the thick rod of impure metal is made the anode and a thin strip of pure metal is made the cathode.

2. The acidified solution of copper sulphate (CuSO4) is used as an electrolyte.

3. Place both the electrodes in the copper sulphate solution. A copper sulphate solution dissociates in to  copper and sulphate ions.

CuSO₄ → Cu²⁺ + SO₄^2-

4. When electricity is passed through the solution, the positively charged copper ions move to the cathode. There the copper ions gain electrons and get deposited as copper metal.

Cu²⁺ + 2e^– → Cu

5. The sulphate ions remain in solution. From the copper anode, copper goes into solution by giving up two electrons, leaving the impurities as anode mud. Thus the strength of the solution remains unchanged.

Cu → Cu²⁺ + 2e^–

CLASS TASK 4

Q1- What is electroplating? Give its advantage.

The process of coating or depositing a thin layer of any desired metal over another metal by the process of electrolysis is called electroplating. Generally objects made of metals  like iron are coated with nickel, chromium, silver and gold by the methods of electroplating.

ADVANTAGES OF ELECTROPLATING

1.     Electroplating is mainly done to prevent metals from corrosion.

2.     It improves the appearance of metals and gives the object a rich look.

3.     It makes the object economical.

Q2- Write an activity to show electroplating of copper over carbon rod.

Answer-

 AIM – To observe Electroplating

4.     MATERIALS  REQUIRED– Glass trough, Copper sulphate solution, A pure copper strip, A carbon rod, Battery, Wires.

5.     PROCEDURE – i)Take copper sulphate solution in a glass trough.

6.     ii) Dip a carbon rod in the solution and use it as the cathode, i.e. connect it to the negative terminal of the battery.

7.     iii) Take a pure copper strip, dip it in the solution and use it as anode, i.e. connect it to the positive terminal.

8.     iv) Pass electricity through the solution by closing the circuit.

9.     Since copper sulphate is an ionic compound, it constitutes ions.

OBSERVATION - When electricity is passed through the solution, the cations from the solution  get attracted and move towards the carbon rod which is acting as the negative electrode, cathode. Here they gain electrons and get deposited as copper metal.

At cathode : Cu2+ + 2e–  → Cu

 At anode : Cu → Cu2+ + 2e –

CONCLUSION -Copper gets electroplated on carbon rod.

( DRAW FIGURE 15.11 of your book)

Q3- Name the factors over which thickness of electroplating depands on.

ANSWER- The thickness of the plating on the articles to be electroplated depends on 

Q4- Give uses of electroplating.