08 October 2014

8th Solved Chemical effects of electric current assignments

Q1. Do liquids also conduct electricity? Name two liquids which conduct electricity and two liquids which do not conduct electricity.

Ans: Two liquids which conduct electricity are : Lemon juice ,Vinegar, Tap water.
Two liquids which do not conduct electricity : Milk, Honey

Q2. Name a device which glows even when a weak electric current passes through it.

Ans: LED [Light Emitting Diode]

Q3.What is electrochemistry? 

Ans: Electrochemistry is defined as the branch of science that deals with chemical effect of electric current.

Q4. Which effect of electric current is utilized for detecting the flow of current through a solution:
a) When a torch bulb is used?    (b) When a compass is used?

Ans: (a) Heating effect              (b) Magnetic effect

Q5. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? .

Ans : No, This is because ordinary water is conductor of electricity and it will be fetal.

Q6. When electric current is passed through acidified water, then hydrogen and oxygen are formed. What type of effect of current is illustrated by this statement?

Ans: Chemical effect of current

Q7. State some of the characteristics of chemical changes brought about by the chemical effect of electric current.

Ans: (a) When electric current is passed through water, water dissociates into hydrogen and oxygen. Hydrogen is deposited over negative pole and oxygen is deposited over positive pole. Deposition of hydrogen and oxygen at different poles is visible in the form of bubbles.

(b) When electric current is passed through the solution of a metal salt, such as solution of copper sulphate, metal gets deposited at the negative pole, because metal is positively charged.

(c) Sometimes, the colour of solution also changes when electric current passes through it.

Q8. Name the metal which is usually electroplated on car parts such as bumpers and  bicycle handlebars made of steel.

Ans: Chromium

Q9. An iron key is to be electroplated with copper. Draw a labeled sketch of the experimental set up used for this purpose.

Ans: Iron rod made as cathode and copper rod as anode and dipped into copper sulphate electrolyte.

Credit: www.brighthubengineering.com
When current passes through copper sulphate split up into ions Cu+2 and SO4-2 Cu+2  move towards catode to gain electron and neutralize as cu and form layer over iron. Copper as anode losse electron and form  Cu+2 move to electrolyte to form CuSO4

Q10. Name two metals which are usually electroplated on cheaper metals for making jewellery (or ornaments).

Ans:chromium and silver and Gold

Q11. You are required to do electroplating of copper on an iron object. Name the positive electrode (anode) and  the electrolyte you will use for this purpose.

Ans: Copper as anode and cathode as a cathode and CuSO4 as electrolyte

Q12. During electroplating the copper deposited on the plate connected to negative terminal comes from the solution. How this loss of copper from solution compensated?

Ans:  From the other plate an equal amount of copper gets dissolved in the  solution. Thus the loss of copper from the solution gets compensated and the process keeps going. This means that copper gets transferred from one plate to another.

Q13. Why does compass needle show more deflection when you test sea water, compared to ordinary water?

Ans: Sea water is more conductor compared to ordinary water as they contain lot of dissolved salt 

Q15. Describe electrolysis of water?

Ans: When electricity passes through water it splits up into H+ and O- ions. H+ move toward cathode to gain electrons to became H2 and  O- move towards anode to lose electrons to became O2

Reduction at cathode: 2 H+(aq) + 2e → H2(g)

Oxidation at anode: 2 H2O(l) → O2(g) + 4 H+(aq) + 4e

Q16. What happens to the needle of a magnetic compass kept nearby when electric current is switched on in a wire? Why does this happen?

Ans:  The needle of a magnetic compass shows deflection when  kept nearby a wire caring current
 as wire behave like a magnet

Q17 Iron is used in bridges and  automobile to provide strength. Which metal is electroplated on iron to protect it from corrosion?

Ans: iron is plated with nickel, chromium, tin, zinc, or cadmium.
Iron used in constructing a building is coated with a layer of zinc. This protects iron from corrosion and rusting.

Q18. We should never handle electrical appliances with wet hands or while standing on a wet floor. Why?

Ans : This is because water  conduct electric current to body and we get shock as water is good conductor.

Q19. When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into the following solution, then in which solution or solutions the compass needle shows deflection. 
Solutions are: Lemon juice, Vinegar, Tap water, Vegetable oil, milk, Honey.

Ans: Lemon juice, Vinegar, Tap water.

Q20.Why does an electric bulb glow when a current passes through it?

Ans:The bulb glows because the electricity which is a form of energy which heats a wire inside of the bulb as it passes through. This gives a glow to the wire which is magnified by the curve of a bulb.

Solution for Basic Science Publication Bharati Bhawan  [Central public School]

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