Extra 20 important long questions and answers for the "Chemical Effects of Electric Current" chapter:11 of Class 8 CBSE Science:-
Q: Explain the process of electrolysis and describe the roles of the anode, cathode, and electrolyte.
A:
Electrolysis is the process of decomposing a chemical compound by passing an electric current through it.
The electrolyte is the liquid or solution that conducts electricity by the movement of ions.
The anode is the positive electrode, which attracts negatively charged ions (anions) and where oxidation occurs.
The cathode is the negative electrode, which attracts positively charged ions (cations) and where reduction occurs.
Ions in the electrolyte move towards the oppositely charged electrodes, resulting in chemical reactions.
These reactions lead to the decomposition of the compound and the deposition or release of substances at the electrodes.
Q: Describe the process of electroplating and explain its applications.
A:
Electroplating is the process of depositing a thin layer of one metal onto another using electrolysis.
The object to be plated is made the cathode, and the plating metal is made the anode.
The electrolyte contains ions of the plating metal.
When an electric current is passed, metal ions from the electrolyte are reduced and deposited onto the cathode.
Applications include corrosion prevention, decorative purposes, and improving wear resistance.
Examples include chromium plating on car parts and silver plating on
jewellery
.
Q: Explain why some liquids conduct electricity while others do not.
A:
Liquids that conduct electricity contain dissolved ions, which are charged particles.
These ions can move freely, allowing the flow of electric current.
Electrolytes, like salt solutions and acidic solutions, contain these ions.
Liquids like distilled water and pure organic solvents lack ions and are poor conductors.
The presence of impurities, especially dissolved salts, increases the conductivity of water.
The ability of a liquid to conduct electricity depends on the concentration and mobility of its ions.
Q: Describe the chemical effects of electric current and give examples.
A:
The chemical effects of electric current refer to the chemical changes caused by the passage of current through a conducting solution.
Electrolysis is a primary example, where compounds are decomposed.
Electroplating is another example, where metals are deposited.
The evolution of gases, like hydrogen and oxygen from water, is a chemical effect.
Changes in the
colour
or composition of the electrolyte can also occur.
The refining of metals through electrolysis is also a chemical effect.
Q: Explain how a magnetic compass can be used to detect the presence of an electric current in a solution.
A:
An electric current flowing through a conductor produces a magnetic field.
A magnetic compass placed near the conductor will show a deflection due to this magnetic field.
If the current is strong enough, the compass needle will deflect noticeably.
This deflection indicates the presence of an electric current.
The direction of the deflection depends on the direction of the current.
This method is useful for detecting weak currents that might not light an LED.
Q: Describe the process of electrolytic refining of metals.
A:
Electrolytic refining is used to purify impure metals using electrolysis.
The impure metal is made the anode, and a thin strip of pure metal is made the cathode.
The electrolyte contains a solution of the metal's salt.
During electrolysis, pure metal ions dissolve from the anode and deposit onto the cathode.
Impurities settle at the bottom as "anode mud."
This process yields a high purity of the metal.
Q: Explain the role of LEDs in electrical circuits and their advantages.
A:
LEDs (Light Emitting Diodes) are semiconductor devices that emit light when an
electric current passes
through them.
They are used to indicate the presence of current in circuits.
LEDs consume very little power compared to traditional bulbs.
They have a longer lifespan and generate less heat.
They are more durable and resistant to shock and vibration.
They are used in many electronic devices, and as indicator lights.
Q: Describe the electrolysis of water and the gases produced at the electrodes.
A:
Electrolysis of water involves passing an electric current through water containing a small amount of acid or salt.
Water molecules are decomposed into hydrogen and oxygen gases.
Hydrogen gas is produced at the cathode (negative electrode).
Oxygen gas is produced at the anode (positive electrode).
The volume of hydrogen gas produced is twice the volume of oxygen gas.
The process demonstrates the chemical breakdown of water by electricity.
Q: Explain the factors that affect the amount of metal deposited during electroplating.
A:
The strength of the electric current affects the rate of metal deposition.
The duration of electrolysis affects the thickness of the deposited layer.
The concentration of the electrolyte affects the availability of metal ions.
The surface area of the cathode affects the amount of metal deposited.
The temperature of the electrolyte can also influence the rate of deposition.
The type of electrolyte used, and the type of metal used for the anode, also
effect
the outcome
.
Q: Describe the uses and importance of coating iron with zinc (galvanization).
A:
Galvanization involves coating iron with a layer of zinc.
Zinc acts as a sacrificial metal, corroding before iron.
This prevents iron from rusting, extending its lifespan.
Galvanized iron is used in construction, pipes, and other outdoor applications.
It is cost-effective and provides long-term protection against corrosion.
This process is important for maintaining infrastructure, and products that are exposed to the elements.
Q: Explain the differences between conductors and insulators and give examples.
A:
Conductors are materials that allow electric current to flow through them easily.
They contain free electrons or ions that can move.
Examples include metals like copper, silver, and iron, and electrolytes.
Insulators are materials that resist the flow of electric current.
They lack free electrons or ions.
Examples include rubber, plastic, wood, and glass.
Q: Describe the process of how a LED emits light.
A:
LEDs are semiconductor devices.
When an
electric current passes
through the LED, electrons recombine with holes within the semiconductor material.
This recombination releases energy in the form of photons, which is light.
The
color
of the emitted light depends on the semiconductor material used.
LED's are very efficient, because most of the energy is turned into light, instead of heat.
The longer lead of the LED is the positive side, and the shorter lead is the negative side.
Q: Explain the importance of using electrolytes in batteries.
A:
Electrolytes are essential components of batteries.
They provide the medium for ion movement, enabling the flow of electric current.
Electrolytes facilitate the chemical reactions that produce electricity.
Different types of batteries use different electrolytes.
The choice of electrolyte affects the battery's voltage and capacity.
Without an electrolyte, the battery would not be able to generate electricity.
Q: Describe the process of copper purification using electrolysis.
A:
Impure copper is used as the anode.
A thin sheet of pure copper is used as the cathode.
A solution of copper
sulfate
is used as the electrolyte.
When current is applied, copper ions dissolve from the anode and deposit on the cathode.
Impurities fall to the bottom of the tank.
This process produces high purity copper.
Q: Explain why it is dangerous to handle electrical appliances with wet hands.
A:
Water is a good conductor of electricity.
Wet hands reduce the body's resistance to electric current.
This increases the risk of electric shock.
Electric current can easily flow through wet skin to the body.
Severe electric shock can cause burns, muscle spasms, and cardiac arrest.
It is essential to keep electrical appliances away from water.
Q: Describe the chemical changes that occur when an electric current is passed through copper
sulfate
solution.
A:
Copper
sulfate
solution is an electrolyte.
When an electric current is passed, copper ions move to the cathode.
Copper metal is deposited on the cathode.
Sulfate
ions move to the anode.
Oxygen gas is released at the anode.
The blue
color
of the copper
sulfate
solution fades over time.
Q: Explain how the strength of an electric current affects the chemical effects observed.
A:
A stronger electric current increases the rate of chemical reactions.
In electrolysis, a
stronger current leads
to faster decomposition of the electrolyte.
In electroplating, a
stronger current results
in a faster rate of metal deposition.
A stronger current can produce more intense chemical changes, such as greater gas evolution.
The strength of the current is directly proportional to the rate of the chemical effects.
Too much current however, could cause unwanted side reactions, or damage the equipment.
Q: Describe the process of tin plating food cans and its importance.
A:
Tin plating involves coating iron cans with a thin layer of tin.
Tin is less reactive than iron, preventing food from reacting with the iron.
This prevents corrosion and preserves the food's quality.
Tin is non-toxic, making it safe for food storage.
Tin plating extends the shelf life of canned foods.
This process is vital for food safety and preservation.
Q: Explain the relationship between the concentration of an electrolyte and its conductivity.
A:
Higher concentration of electrolyte means more ions.
More ions result in higher conductivity.
Diluted electrolytes have fewer ions and lower conductivity.
The conductivity is directly proportional to the concentration of ions.
The mobility of ions also affects conductivity.
Very high concentrations of some electrolytes could decrease the mobility of the ions, and therefore decrease the conductivity.
Q: Describe how to safely test if a liquid conducts electricity.
A:
Use a battery, LED, and connecting wires.
Connect the LED and wires to the battery.
Place the free ends of the wires into the liquid.
Observe if the LED lights up.
If the LED lights up, the liquid conducts electricity.
Ensure the voltage is low to prevent electric shock, and do not touch the liquid while the current is flowing.
