CHEMICAL EFFECTS OF ELECTRIC CURRENT Class 8 Chapter 14

 Introduction-Current is the flow of charges through a conducting wire or liquid. Those materials through which current can flow are called as conductors. e. g- Metal wires, Conducting liquids having electrolyte, . Those materials through which current cannot flow are called as poor conductors or insulators. e. g- Plastic, Dry wood, Paper, Distilled water, Edible oils, like Mustard oil, Coconut oil, Milk, Honey etc.

Do liquids conduct electricity?- Whether the liquid will conduct the current of not it depends on the minerals –salts dissolved in it. The mineral salts, acids and bases act as conductor of current in water or any similar liquid.

A simple electric circuit was prepared using battery, connecting wire, switch and magnetic compass. The compass was kept in a match box and connecting wire is wrapped around it. The two open ends of connecting wires were kept in a beaker having tap water. When current passes through the circuit, defection of needle of magnetic compass was seen. It showed that tap water is a conductor of current. Similarly, when beaker of tap water was replaced by distilled water, there was no deflection in the compass. It showed that distilled water is an insulator of current owing to the lack of mineral-salts.

S.N.	MATERIAL	DEFLECTION IN COMPASS NEEDLE   (YES/NO)	GOOD /POOR CONDUCTOR
1	Tap Water	Yes	Good Conductor
2	Milk	Yes	Good Conductor
3	Mustard Oil	No	Poor Conductor
4	Vinegar	Yes	Good Conductor
5	Lemon Juice	Yes	Good Conductor
6	Honey	No	Poor Conductor
7	Distilled Water	No	Poor Conductor
8	Salt+ Distilled Water	Yes	Good Conductor

LED-(Light Emitting Diodes) - The smaller L.E.Ds glow even at very less current of 0.3 V. They are available in form of bulb and tube lights also. They consume comparatively less current than bulbs and C.F.Ls. There are two wires attached to L.E.Ds called leads. One lead is longer than the other. Loner one is connected with positive terminal of the battery while smaller one is connected with negative terminal of the battery.

Chemical Effects of electric current- When current is allowed to passes through any solution, either current passes through it or not. The solutions behave as conductors when mineral-salts remain dissolved in them. Sometimes when an electrolyte (that dissociates into ions on passing current) is dissolved as solute, then also the solution behaves as a conductor. Ions are charged particles that are formed on dissociation of an electrolyte when current passes in its solution.

e.g.- The sodium chloride (common edible salt) is an electrolyte that dissociates into its ions on passing the current in its solution.

NaCl (Sodium Chloride) -----------> Na ⁺ (Sodium Ion)  +  Cl ^– (Chlorine Ion)

The positively charged ion is called cation and negatively charged ion is called as anion. This breaking of any electrolytic compound into their constituent ions is called as electrolysis. This happens when there are two plates in the electrolytic cell, connected to the positive and negative terminal of the battery.  The two metal plates are called as electrodes- Cathode and Anode. Cathode remains connected with negative terminal of the battery and anode remain connected to the positive terminal of the battery. During the electrolysis the cations go to cathode and anions go to anode electrode/terminal. Electrolysis is a chemical effect of electric current.

Electrolytes are solutions of acids, bases and salts. The ions help in carrying the charges.

Electroplating- The electrolysis has many scientific and industrial applications. One of the important applications is electroplating. Electroplating is a process of coating of a layer of desired metal on another material by means of electric current. Electroplating is done to protect the object from rusting, scratching or to make it more attractive.

The strip of metal whose coating is to be done is taken as anode. The metal to be electroplated is taken as cathode. The electrolyte is taken as the soluble salt of metal hose coating is to be done at anode. Generally, nickel, gold, silver, chromium, platinum like metals are coated over a relatively less expensive metal object.  The proper cleaning of metal object to be electroplated and supply of current of suitable strength is essential for long lasting electroplating.

Exercise Questions-

Q.1 Fill in the blanks

(a) Most liquids that conduct electricity are solutions of ………..and ……………

(b) The passage of an electric current through a solution causes ……………….. effects.

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

(d) The process of depositing a layer of any desired metal by means of electricity is called …………..

Ans- (a) acids, bases (alkali) and salts      (b) chemical      (c) negative    (d) electroplating

Q.2 When the free end of a tester is dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

A

 

 

 

 

 

 

 

Electro-refining- The metals are extracted from their ores. For extraction of metal, such metal ores are taken in which metal is found in comparatively maximum percentage.

GREEN Olympiad - Responsibility Towards the Planet

Please Watch This Video Pertaining to Environment Related Issues 

RESPIRATION IN ORGANISMS Class 7 Chapter 10

 Key Learning Points- Respiration, Breathing, Breathing rate, Inhalation, Exhalation, Respiratory system, Cellular(Internal) Respiration, Aerobic respiration, Anaerobic Respiration, Transpiration, Gills, Spiracles, Trachea(Wind Pipe)

Introduction- We need energy to do every kind of work. This energy is obtained from oxidation i.e. burning of digested food in presence of oxygen inside the cells. In oxidation of food oxygen is taken, carbon dioxide gas is released and biological energy A.T. P.s (Adenosine triphosphate) are generated.

The process by which the digested and absorbed food (glucose) is oxidized to release the energy is called respiration.

Respiration occurs in two phases-

1. Breathing/ External respiration

2. Cellular/ Internal Respiration

1. Breathing / External respiration- The taking of oxygen rich air inside the lungs is called inhalation. The releasing of carbon-dioxide rich fowl air from the lungs is called exhalation. Breathing comprises both inhalation and exhalation.

Breathing Rate- The number of inhalation and exhalation per minute by a person is called breathing rate. In infants and children, the breathing rate is higher than an old person. During sleeping the breathing rate is less than the breathing rate during any activity like playing.

The average breathing rate in an adult person is 15-18 times.

2. Cellular/ Internal Respiration- The glucose is raw material for oxidation inside the cell. Here the enzymes and oxygen helps in synthesis of biological energy A.T.Ps. It is done in the mitochondria of cells. So, mitochondria are called ‘power house of the cell.’

BREATHING	RESPIRATION
It is a physical process.	It is a biochemical process.
It occurs outside the cells.	It occurs inside the cells.
Inhalation and exhalation occurs.	Oxidation of digested food occurs.
No energy is released.	Energy (A.T.P.) is released.

Types of cellular Respiration- There are two types of cellular respiration-

(a) Aerobic Respiration- The respiration that takes place inside the cells in presence of oxygen is called as aerobic respiration. The glucose is broken into carbon dioxide gas, water and ATPs.

Glucose + Oxygen -----> Carbon dioxide + Water + 36 A.T.Ps

(b)Anaerobic Respiration- The respiration that takes place in absence or partial presence is called as anaerobic respiration. On this basis there are two types of anaerobic respiration-

(b.1) Anaerobic Respiration in absence of oxygen/Fermentation-- The yeast cells in absence of oxygen prepare ethyl alcohol, carbon dioxide and little amount of A.T.Ps. Due to formation of carbon dioxide gas yeast is used in bakery to make bread.

Glucose ---Absence of Oxygen -----> Ethyl alcohol (or Ethanol) + Carbon dioxide + 2 A.T.Ps

This type of reaction is also called as fermentation. The alcohol production is called brewing. It is a very old method of wine preparation.

(b.2) Anaerobic Respiration in partial presence of oxygen-When muscles are working very actively and supply of oxygen upto the fatigue muscles becomes limited then anaerobic respiration occurs. As a result the lactic acid is formed in fatigue painful muscles cramps are caused.

Glucose ---Partial presence of Oxygen -----> Lactic Acid + 2 A.T.Ps

AEROBIC  RESPIRATION	ANAEROBIC RESPIREATION
Occurs in presence of oxygen	Occurs in absence or partial presence of oxygen
Carbon dioxide gas and water are produced.	Ethyl alcohol, carbon dioxide gas or lactic acid are produced
36 A.T.Ps are released from one glucose.	2 A.T.Ps are released from one glucose.
Takes place all the time in living organisms.	Takes place for a short duration on living organisms.

Human Respiratory System – It consist of nose having nostrils, pharynx- common  passage for food and air and having muscular flap called epiglottis, trachea having larynx /Adam’s apple, bronchi, bronchioles and alveoli.

Mechanism of Respiration- The mechanism of respiration consists of inhalation and exhalation of air. During inhalation, the volume of chest cavity increases due to downward movement of diaphragm and upward and outward movement of ribs. The air pressure inside the chest gets reduced than the outside atmosphere. So, the oxygen rich air is inhaled.

During exhalation, the volume of chest cavity decreases due to back movement of diaphragm and ribs.

The air pressure inside the chest cavity is increased than the outer atmosphere as a result the carbon dioxide rich fowl air comes out.

Respiratory Gases percentage

Breathing form Gas Percentage	Inhalation	Exhalation
% of Oxygen	20.14 %	16.3 %
% of Carbon Dioxide	0.04 %	4.4%

 

Activity- To prove that CO2 Gas is released during exhalation- Requirements- Lime Water (Calcium hydroxide), blowing glass/steel pipe, dropper and test tube Procedure- In a test tube, lime water was gently taken with the help of a dropper. The air to be breath out is passed to lime water by blowing pipe. It was repeated about 10-15 times. Result- The light blue coloured lime water turned into milky white colour. It is due to formation of calcium carbonate. Lime water + Carbon dioxide (from exhalation) ----> Calcium carbonate (milky white) Ca(OH)2 + CO2 ---> CaCO3

Respiration in other organisms-

1. Insects- The insects have tracheal system as their respiratory system. The air is inhaled and exhaled through small pores ‘spiracles’ present on the side of their body.

2. Earthworm- The exchange of respiratory gases like oxygen and carbon dioxide occurs through thin and moist skin by diffusion. It is an example of cutaneous respiration.

3. Fish- Many of the bony fishes have ‘Gills’. The gills help in taking of oxygen dissolved in water and carbon dioxide is released through mouth.

4. Plants- The leaves have minute pores called ‘stomata’. Through stomata exchange of oxygen and carbon dioxide gas takes place. In the roots the exchange of gases occurs through the root has and outer epidermal cells by diffusion.

EXERCISE QUESTIONS-

Q.1 Why does an athlete breathe faster and deeper than usual after finishing the race?

Ans-

 

 

 

 

 

 

 

 

 

SOUND CHAPTER 13 CLASS 8

Key Learning Points- Vibrations, Larynx (Voice box), Medium of sound propagation, Human ear, Properties of sound- Amplitude, Time period and Frequency, Audible range of sound, Noise and music , Noise pollution

Introduction- In our surrounding we hear sound of different varieties. Some of them are sweet and pleasant while some others are loud and irritating. The chirping of birds, ringing of bell, sound of flute etc. are all sounds. Some sounds are louder and some others are shrill. The voice box (larynx) in humans produces sound. The sound is produced because of vibration of any object. Sound has different properties and uses. Sound propagates maximum in solids, then in liquids and least in gases.

Sound is produced by vibration- Vibrations are the to and fro movement of any membrane or object. It is a periodic motion. When rubber band is plucked, striking of a steel disc by spoon, striking a pan, Jaltarang etc. sound is produced.

The musical instruments have their vibrating parts which produce sound on striking.

The musical instruments are classified in three types on the basis of their type of sound producing part-

1. Stretched/Vibrating String- Veena, Sitar, Guitar, Violin, Ektara etc.

2. Stretched/Percussion membrane- Tabla, Drums, Pakhawaj etc.

3. Vibrating air column- Flute, harmonium, Mouth organ, Ghatam, Jaltarang, Pepa etc.

Sound Produced by Humans- When we speak whisper, buzz or scream we can feel the vibrations by keeping our hand on throat. These vibrations are produced by our voice box (larynx) when we speak. The voice box is found in neck as protruded hard bump. It is the upper end of wind pipe. Voice box is a thin slit of trachea (windpipe) through which air passes. On both side of the voice box, vocal cords are found. They vibrate on passing of air. The muscles attached to vocal cords also help in its vibration. The thin and tight vocal cords produce high pitch shrill sound. The loose and thick vocal cords produce low pitch hoarse voice.

 

Medium of Propagation of sound- The sound is a mechanical wave that requires any medium to travel from one place to other. Through any medium it transfers it’s energy. Sound cannot travel through vaccum. The density of solids is more than liquids and gases; therefore, sound propagates easily in solid medium.  Similarly, it propagates comparatively faster in liquids than gases.

Speed of Sound in Iron- Approximately 5000 m/s

Speed of Sound in water- Approximately 1400 m/s

Speed of Sound in Gases/ Air- 332 m/s

Speed of Sound in Solids > Speed of Sound in Liquids > Speed of Sound in Gases   

Human ear- We hear the sound through our ears. The shape of ear pinna is like a funnel. When sound enters in ear, it goes into the ear (auditory) canal. At the end of auditory canal a tightly stretched thin membrane called eardrum (tympanic membrane) is found. The eardrum vibrates due to sound vibrations. Then vibrations go to inner ear. The 3 smallest bones (malleus, incus and stapes) help in increasing the vibrations. These vibrations are changed into electric impulses/signals that go to brain through auditory nerves.

Cleaning of ear and safety of eardrum is essential. The injured eardrum is not repairable. It causes leakage of pus.

Properties of sound- There are three main characteristics of a sound wave. These are Amplitude, Time period and Frequency.

The to and fro motion is called as vibration or oscillatory or periodic motion or simple harmonic motion. The time taken to complete one oscillation is called as time period. Sound wave is also a vibration. The two sounds are different from each other due to their qualities like amplitude and frequencies.

A. Amplitude-Amplitude of a sound wave is the maximum displacement of medium’s particles.  It is represented by symbol ‘A’. Since, it a displacement of particles therefore it’s S.I. unit is meter ‘m’. The loudness of sound is determined by amplitude of sound. Higher is the amplitude, louder is the sound. When the amplitude is smaller , sound will be feeble.

Loudness of the sound is proportional to the square of the amplitude of the vibration producing the sound. Loudness is directly proportional to the square of amplitude - Loudness ∝A². It means when amplitude becomes twice, the loudness of sound increases by four times. The unit of loudness of sound is decibel (dB). Sounds above 80 dB are painful to hear by humans.

B. Frequency – Number of oscillations per second is called frequency. The S.I. unit of sound is Hertz (Hz) / Cycle per second. Frequency of sound determines the shrillness or pitch of the sound. The shrill sounds have more frequencies. The hoarse sounds have less frequency. The sound of drum has low frequency and high amplitude but the sound of whistle has very high frequencies and comparatively low amplitude. The roar of lions has low frequencies and chirping of birds has high frequencies. Galton’s Whistle

AUDIBLE AND INAUDIBLE SOUNDS- For humans, the range of audible frequencies is between 20 Hz to 20,000 Hz. The sound below 20 Hz is called as infrasonic sound and sound above 20, 000 Hz is called ultrasonic sound. Both, infrasonic and ultrasonic sound cannot be listened by human ear. Dogs can listen sound above 20 K Hz (or 20 ,000 Hz). So, police uses Galton’s Whistle to keep dogs away or give command. Ultrasound is used in medical diagnosis. Infrasonic sound is produced by Whale, Elephant, Rhinoceros, Hippopotamus etc. Ultrasonic sound is produced by Bat, Grasshopper, Frog, Whale, Dolphins etc.

Music- Pleasant sound is called music. It is melodious and pleases us.  It has certain vibrations that have particular and repeated sound. These sounds have fixed amplitude generally and frequencies.

Noise- Unpleasant sound is called noise. It disturbs us. It has different amplitude and different frequencies.

NOISE POLLUTION- The presence of excessive undesirable sound in the environment is called as noise pollution. The sources of noise pollution are- speakers, aeroplanes, jet planes, machines, crackers etc. The noise pollution may become deaf, causing anxiety, sleeplessness, hypertension (high blood pressure) and health disorders are caused.

The silencing devices in machines, vehicles, home appliances, aircrafts etc must be installed to reduce noise pollution. The sound absorbing wood panels and cotton curtains, clothes etc. are good to reduce noise pollution. This is the reason why empty room causes echo on speaking while room with clothes, curtain and wooden furniture does not produce echo.

The reduce hearing impairment can be improved by hearing aids.

 EXERCISE QUESTIONS-

Q.1 Choose the correct answer- Sound can travel through

(a) gases only                 

(b) solids only

(c) liquids only               

(d) solids, liquids and gases

Ans- (d) solids, liquids and gases

Q.2 Which of the following voices is likely to have minimum frequency?

(a) Baby girl

(b) Baby boy

(c) A man 

(d) A woman

Ans- (c) A man 

Q.3 I which of the following statements, tick T against those which are true, and F against those which are false:

(a)