Lakhmir singh solutions science class 8 Solutions for Chapter 14 chemical effect of electric current

Do liquids also conduct electricity?

Name two liquids which conduct electricity and two liquids which do not conduct electricity.

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

Write the full form of LED.

How would you classify lemon juice- a good conductor or a poor conductor of electricity?

Vinegar is a sour liquid. State whether vinegar will conduct electricity or not.

What effect does electric current produce when flowing through a conducting liquid (or conducting solution)?

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

Acidified water is electrolyzed by using carbon electrodes. What is produced at: (a) Positive carbon electrode?

(b) Negative carbon electrode?

Give one example of the chemical effect of electric current.

What should be done to decompose water into hydrogen and oxygen?

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

Name two metal objects which have a coating of another metal.

Name the most common application of the chemical effect of electric current.

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

Which is the polluting waste generated by electroplating factories?

Name two metals which are purified by using the chemical effect of current (or electrolysis).

Name two metals which are produced (or extracted) by using the chemical effect of electric current.

Name one chemical compound which is produced by using the chemical effect of electric current.

Name one compound which is decomposed into hydrogen and oxygen by using the chemical effect of electric current.

State whether the following statements are true or false:

(a) Rainwater is a non-conductor of electricity.

(b) A piece of fresh potato does not conduct electricity at all.

Fill in the following blanks with suitable words:

(a) Most liquids that conduct electricity are solutions of ________, ________ and ________

(b) The LED glows even when a ________ electric current passes through it.

(c) The passage of an electric current through a conducting solution causes ________ effect.

(d) When an electric current is passed through acidified water, then ________ and ________ are formed.

(e) The process of depositing a layer of any desired metal on another metal by means of electricity is called ________

(f) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ________ terminal of the battery.

Which of the following liquids conduct electricity and which do not conduct electricity?

Lemon juice, Milk, Vinegar, Common salt solution, Sulphuric acid solution, Sugar solution, Distilled water, Honey, Seawater, Rainwater.

Why is it dangerous to touch a working electrical appliance with wet hands?

What is the advantage of using LED in testing the electrical conductivity of liquids?

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?

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

Explain why distilled water does not conduct electricity but tap water conducts some electricity.

Distilled water does not conduct electricity. What substances can be added to distilled water in small amounts to make it a good conductor of electricity? Why?

Which of the two is a better conductor of electricity: drinking water (tap water) or seawater?

Give the reason for your answer.

Why does a brand new bicycle have shining handlebar and wheel rims? What will happen if these are accidentally scratched?

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

When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into a solution, the magnetic needle shows deflection. Can you give the reason for this deflection?

A beaker contains an acidified copper sulphate solution. A copper plate and a carbon rod are kept in this copper sulphate solution. The copper plate is connected to the positive terminal of a battery whereas the carbon rod is connected to the negative terminal of the battery. What will you observe when an electric current is passed through this set-up for a considerable time?

Does pure water conduct electricity? If not, what can we do to make it conducting?

In case of a fire, before the firemen use the water hoses to throw water to douse a fire, they shut off the electricity supply for the area. Explain why this is done.

(a) Which effect of electric current is utilized when a thin layer of chromium metal is deposited on an iron tap? What is this process known as?

(b) For electroplating copper on an iron object, which terminal of the battery (positive or negative) is connected to the iron object? Also, name the electrolyte you will use for this purpose.

Inactivity to check the conduction of electricity through two liquids labelled A and B by using a bulb, it is observed that the bulb glows brightly for liquid A while it glows very dimly for liquid B.

(a) Liquid A is a better conductor than liquid B

(b) Liquid B is a better conductor than liquid A

(c) Both liquids are equally conducting

(d) Conducting properties of liquids cannot be compared in this manner.

Which of the following does not conduct electricity?

(a) Vinegar solution

(b) Sugar solution

(c) Lemon juice solution

(d) Caustic soda solution

Which of the following metals should be electroplated on a tiffin box made of steel?

(a) Copper

(b) Chromium

(c) Silver

(d) Tin

Which of the following metal are produced by the electrolysis of their molten compounds?

A. Copper B. Silver C. Aluminium D. Sodium

Which of the following types of energy can be used to decompose water into its elements?

(a) Heat energy

(b) Light energy

(c) Chemical energy

(d) Electrical energy

Which of the following objects should not be chrome-plated?

(a) Car bumper

(b) Gas stove

(c) Frying pan

(d) Bicycle bell

Which of the following is a weak electrolyte:

(a) Carbonic acid.

(b) Sodium hydroxide.

(c) Copper sulphate.

(d) Nitric acid.

Non-metals are generally non-conductors of electricity. The non-metal whose one of the forms can be used to make electrodes in electrolysis experiment is:

(a) Iodine

(b) Carbon

(c) Silicon

(d) Phosphorus

The decomposition produced by passing a current through a conducting liquid is called:

(a) Dialysis

(b) Hydrolysis

(c) Electrolysis

(d) Electroplating

Which of the following is not an application of the chemical effect of electric current?

(a) Electroplating of metals

(b) Purification of metals

(c) Decomposition of elements

(d) Decomposition of compounds

One of the following is not used for electroplating metal articles. This one is:

(a) Nickel

(b) Chromium

(c) Sodium

(d) Silver

An arrangement having two carbon rods kept in a conducting liquid in a vessel known as:

(a) Rechargeable cell

(b) Storage cell

(c) Biological cell

(d) Electrolytic cell

Which of the following effects is not produces by the chemical reactions brought about by electric current?

(a) Bubbles of gases on electrodes

(b) Deposits of metal on electrodes

(c) Change in colour of the solution

(d) Formation of a precipitate

Which of the following can be electroplated with chromium?

A. Bakelite B. Graphite C. Steel D. Teflon

(a) A and B

(b) B and C

(c) Only C

(d) B and D

To obtain a coating of silver metal on a flower vase made of copper, the electrolyte has to be:

(a) Silver nitrate solution

(b) Copper nitrate solution

(c) Sodium nitrate solution

(d) Copper sulphate solution

If plus sign (+) denotes the positive electrode and minus sign (-) denotes the negative electrode, then which of the following statement is correct for an iron spoon to be copper-plated?

(a) Iron spoon (+), copperplate (-), Iron sulphate electrolyte

(b) Iron spoon (-), copperplate (+), Iron sulphate electrolyte

(c) Copperplate (-), iron spoon (+), copper sulphate electrolyte

(d) Copperplate (+), iron spoon (-), copper sulphate electrolyte