Class 6 back exercise

 Chapter 1 "Food : Where does it come from?"

Q. 3. Match the items given in column A with those in column B.

1. Milk , curd, paneer , ghee --> all are animal products

2. Spinach , Cauliflower, carrot --> are vegetables.

3. Lions and tigers --> eat other animals

4. Herbivores --> eat plants and plant products.

. 4. Fill up the blanks with the words given:
herbivore, plant, milk, sugarcane, carnivore.
(a) Tiger is a__________ because it eats only meat.
(b) Deer eats only plant products and so is called______________ .

(c) Parrot eats only__________

(d) The_________ that we drink, which comes from cows, buffaloes and goats is
an animal product.
(e) We get sugar from___________ .

Ans. (a) carnivore                                (b) herbivore            

(c) plant

(d) milk                             

(e) sugarcane

Chapter 2 " Components of food"

 1.Name the major nutrients in our food.
Ans: The major nutrients in our food are carbohydrates, proteins, fats, vitamins and minerals.

2. Name the following: 
(a) The nutrients which mainly give energy to our body.
(b) The nutrients that are needed for the growth and maintenance of our body.
(c) A vitamin required for maintaining good eyesight.
(d) A mineral that is required for keeping our bones healthy.

Ans:
(a) Carbohydrates
(b) Proteins
(c) Vitamin A
(d) Calcium

 3.Name two foods each rich in:
(a) Fats
(b) Starch
(c) Dietary fibre
(d) Protein
Ans:
(a) Ghee, butter,
(b) Raw potato, rice,
(c) Spinach, cabbage, carrot, ladies finger, (any two)
(d) Milk, egg, fish, meat, pulses (any two).

 4.Tick(✓) the statements that are correct, cross (X) those which dire incorrect.
(a) By eating rice alone, we can fulfill nutritional requirement of our body,
(b) Deficiency diseases can be prevented by eating a balanced diet.
(c) Balanced diet for the body should contain a variety of food items.
(d) Meat alone is sufficient to provide all nutrients to the body.

Ans:- (a) X (b) ✓ (c) ✓ (d) X

5.Fill in the blanks:
(a) ________ is caused by deficiency of Vitamin D. ,
(b) Deficiency of_________ causes a disease known as beri-beri.
(c) Deficiency of Vitamin C causes a disease known as________________ .
(d) Night blindness is caused due to deficiency of_______________ in our food.

Ans:
(a) Rickets
(b) Vitamin B1
(c) Scurvy
(d) Vitamin A

Chapter 3 Fibre to fabric

.2. State whether the following statements are ‘true’ or false’:
(a) Yam is made from fibres.
(b) Spinning is a process of making fibres.
(c) Jute is the outer covering of coconut.
(d) The process of removing seeds from cotton is called ginning.
(d) Weaving of yam makes a piece of fabric.
(e) Silk fibre is obtained from the stem of a plant.
(g) Polyester is a natural fibre.
Ans.
(a) True
(b) False
(c) False
(d) True
(e) True
(f) False
(g) False

Q.3. Fill in the blanks:
(a) Plant fibres are obtained from____________ and___________ .
(b) Animal fibres are___________ and___________ .
Ans.
(a) cotton plants, jute plants
(b) wool, silk

Chapter 4 Sorting Materials into groups

1. Name five objects which can be made from wood.

Ans.

(i) Table , (ii) Chair ,(iii) Doors ,(iv) Boat, (v) Bed

Q.2. Select those objects from the following which shine:

Glass bowl, plastic toy, steel spoon, cotton shirt

Ans. Glass bowl and steel spoon are shining objects.

Q.3. Match the objects given below with the materials from which they could be made. Remember, an object could be made from more than one material and a given material could be used for making many objects.

Book --> paper

Tumbler--> glass

Chair --> wood

Toy--> plastics

Shoes--> leather

Q. 4. State whether the statements given below are ‘true’ or ‘false’.

(i) Stone is transparent, while glass is opaque.

(ii) A notebook has lustre while eraser does not

(iii) Chalk dissolves in water.

(iv) A piece of wood floats on water.

(v) Sugar does not dissolve in water.

(vi) Oil mixes with water. 

(vii) Sand settles down in water.

(viii) Vinegar dissolves in water.

Ans.

(i) False , (ii) False , (iii) False , (iv) True , (v) False , (vi) False , (vii) True , (viii) True

Q. 5. Given below are the names of some objects and materials:

 Water, basket ball, orange, sugar, globe, apple and earthen pitcher Group them as:

(a) Round shaped and other shapes

(b) Eatables and non-eatables

Ans.

(a) (i) Round shaped: Basket ball, apple, orange, globe, earthen pitcher.

(ii) Other shapes: Water, sugar.

(b) (i) Eatables: Water, orange, sugar and apple.

(ii) Non-eatables: Basket ball, globe and earthen pitcher.

Q. 6. List all the items known to you that float on water. Check and see if they will float on an oil or kerosene.

Ans. (A) List of some items that float on water:

Paper, Wood, Thin plastic sheets, Wax, Ice ,Oil and Thermocol

(B) List of items that float on an oil:

Paper , Plastic sheet ,Wax, Thermocol, Wood

(C) List of items that float on kerosene:

Paper, Thermocol, Thin plastic sheet

Q. 7. Find the odd one out from the following:

(a) Chair, Bed, Table, Baby, Cupboard

(b) Rose, Jasmine, Boat, Marigold, Lotus

(c) Aluminium, Iron, Copper, Silver, Sand

(d) Sugar, Salt, Sand, Copper sulphate

Ans.

(a) Baby (all others are non-living)

(b) Boat (all others are flowers)

(c) Sand (all others are metals)

(d) Sand (all others are soluble in water)

Chapter 5

8. Fill in the blanks:
(a) The method of separating seeds of paddy from its stalks is called .
(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream (malai) is left behind on it. This process of separating cream from milk is an example of ______. 
(a) Salt is obtained from sea water by the process of ____________ .
(b) Impurities settled at the bottom when muddy water was kept overnight in a bucket. The clear water was then poured off from the top. The process of separation used in this example is called ____________.
Ans.
(a) threshing
(b)filtration
(b) evaporation
(d) sedimentation and decantation

 True or false?
(a) A mixture of milk and water can be separated by filtration.
(b) A mixture of powdered salt and sugar can be separated by the process of winnowing.
(c) Separation of sugar from tea can be done with filtration.
(d) Grain and husk can be separated with the process of decantation.
Ans.
(a) False
(b) False
(c) False
(d) False

Chapter 6 

1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

Ans: Yes, it can be reversed by unfolding the dress.

2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

Ans: No, this change (breaking of toy) cannot be reversed.

3.Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?

Ans: No, the change in POP cannot be reversed since it is a chemical change.

7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

Ans. No, these are irreversible chemical changes.

Chapter 7 

1.Correct the following statements and rewrite them in your notebook.

(a) Stem absorbs water and minerals from the soil.

(b) Leaves hold the plant upright.

(c) Roots conduct water to the leaves.

(d) The number of sepals and petals in a flower is always equal.

(e) If the sepals of a flower are joined together, its petals are also joined together,

(f) If the petals of a flower are joined together, then the pistil is joined to the petal.

Ans:a) Roots absorb water and minerals from the soil.

(b) Roots hold the plant upright.

(c) Stem conducts water to the leaves.

(d) The number of petals and sepals in a flower is usually equal.

(e) If the sepals of a flower are joined together, its petals are not necessarily joined together.

(f) If the petals of a flower are joined together, then the pistil is not necessarily joined to the petal.

3. Can you find a plant in your house or in your neighbourhood which has a long but a weak stem? Write its name. In which category would you classify it?

Ans: Yes, we find a money plant in our house. It is a climber.

5.Which of the following leaves have reticulate venation?

Wheat, tulsi, maize, grass, coriander (dhania), china rose.

Ans: Tulsi, china rose.

6. If a plant has fibrous root, what type of venation are its leaves likely to have? 

Ans: Parallel venation.

7. If a plant has leaves with reticulate venation, what kind of roots will it have?

Ans:Tap root.

Chapter 8 

Fill in the blanks:

(a) Joints of the bones help in the_____________ of the body.

(b) A combination of bones and cartilages forms the_______________ of the body.

(c) The bones at the elbow are joined by a______________

(d) The contraction of the____________ pulls the   bones  during  

Ans: 

(a) movement, (b) skeleton, (c) hinge, (d) muscle

2. Indicate ‘true’ and false’ among the following sentences:

(a) The movement and locomotion of all animals is exactly the same.

(b) The cartilages are harder than bones.

(c) The finger bones do not have joints.

(d) The fore arm has two bones.

(e) Cockroaches have an outer skeleton.

Ans: 

(a) False , (b) False , (c) False , (d) True , (e) True

Match the items in column I with one or more items of column II:

Upper jaw--> is an immovable joint

Fish --> have a streamlined body and have find on the body

Ribs --> protect the heart

Snail--> shows very slow movement

Cockroach--> can fly in the air.

Chapter 9

Fill in the blanks:

(a) The presence of specific features which enables a plant or an animal to live in a particular habitat is called___________ .

(b) The habitats of the plants and animals that live on land are called _________________ habitats.

(c)The habitats of plants and animals that live in water are called ____________________ habitats.

(d) Soil, water and air are the____________ factors of a habitats.

(e) Changes in our surroundings that make us respond to them are called

Ans: 

(a) adaptation

(b) terrestrial

(c) aquatic

(d) abiotic

(e) stimuli

4. Which of the things in the following list are non-living?

Ans: Plough, Mushrooms, Sewing machine, Radio, Boat, Water, Hyacinth, Earthworm. Plough, Sewing machine, Radio, Boat and water are non-living.

6.Which of the following non-living things were once part of a living thing?

Butter, Leather, Soil, Wool, Electric Bulb, Cooking Oil, Salt, Apple, Rubber.

Ans: Butter, Leather, Wool, Cooking oil, Apple and Rubber are the non-living things which were once part of a living thing.

Chap 10 motion and measurement of distances

2. Fill in the blanks:

(i) One metre is___________

(ii) Five kilometre is___________

(iii) Motion of a child on a swing is_____________ .

(iv) Motion of the needle of a sewing machine is_______________ .

(v) Motion of wheel of a bicycle is_____________ .

Ans:

(i) 100

(ii) 5000

(iii) periodic (oscillatory) motion

(iv) periodic oscillatory (v) circular

4. Arrange the following lengths in their increasing magnitude :

1 metre, 1 centimetre, 1 kilometre, 1 millimetre.

Ans: Ascending order of length:

1 millimetre < 1 centimetre < 1 metre < 1 kilometre

Chap 11

1. Rearrange the boxes given below to make a sentence that helps us understand opaque objects.

Ans:-

2. Classify the objects or materials given below as opaque, transparent or translucent and luminous or non-luminous:

Air, water, a piece of rock, a sheet of aluminium, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the fame of a gas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh, kerosene stove, sun, firefly, moon.

Ans:

Chapter 12

1. Fill in the blanks:

(a) A device that is used to break an electric circuit is called_______________

(b) An electric cell has___________

Ans:

(a) switch , (b) two

2. Mark ‘True’ or ‘False’ for the following statements:

(a) Electric current can flow through metals.

(b) Instead of metal wires, a jute string can be used to make a circuit.

(c) Electric current can pass through a sheet of thermocol.

Ans:

(a) True , (b) False , (c) False

Chapter 13

Fill in the blanks in the following:

(i) Artificial magnets are made in different shapes such as_________ ,_______ and

(ii) The materials which are attracted towards a magnet are called_________

(iii) Paper is not a________

(iv) In olden days, sailors used to find direction by suspending a piece of 

(v) A magnet always has ________poles.

Ans:

(i) bar magnet, horse-shoe magnet and cylindrical magnet

(ii) magnetic materials

(iii) magnetic

(iv) bar magnet or lode stone

(v) two or a pair of

2. State whether the following statements are true or false:

(i) A cylindrical magnet has only one pole.

(ii) Natural magnets were discovered in Greece.

(iii) Similar poles of a magnet repel each other.

(iv) Maximum iron filings stick in the middle of a bar magnet when it is brought near them.

(v) Bar magnets always point towards North-South direction when suspended freely in air.

(vi) A compass can be used to find East-West direction at any place.

(vii) Rubber is a magnetic material.

Ans: 

(i) False

(ii) True

(iii) True

(iv) False

(v) True

(vi) True

(vii) False

4.  Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting action between them for each situation. Fill in the blanks.

10. A magnet was brought from different directions towards a toy boat that has been floating in water in a tub. Effect observed in each case is stated in Column I. Possible reason for the observed effects are mentioned in Column II. Match the statements given in Column I with those in Column II

Ans

Chapter 14

1.Fill up the blanks in the following:

(a) The process of changing of water into its vapour is called_______________ .

(b) The process of changing water vapour into water is called_____________ .

(c) No rainfall for a year or more may lead to _____________ in that region.

(d) Excessive rains may cause__________ .

Ans:

(a) evaporation or vaporisation , (b) condensation , (c) droughts , (d) flood

2. State for each of the following whether it is due to evaporation or condensation:

(a) Water drops appear on the outer surface of a glass containing cold water.

(b) Steam rising from wet clothes while they are ironed.

(c) Fog appearing on a cold winter morning.

(d) Blackboard dries up after wiping it.

(e) Steam rising from a hot girdle when water is sprinkled on it.

Ans: 

(a) condensation , (b) evaporation , (c) condensation ,(d) evaporation

3. Which of the following statements are “true”?

(a) Water vapour is present in air only during the monsoon.

(b) Water evaporates into air from oceans, rivers and lakes but not from the soil.

(c) The process of water changing into its vapour is called evaporation.

(d) The evaporation of water takes place only in sunlight.

(e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler.

Ans: 

(a) False , (b) False , (c) True , (d) False , (e) True.

Chapter 15

2. Which gas in the atmosphere is essential for respiration?

Ans: Oxygen.

6. The layer of air around the earth is known as………………….

Ans: Atmosphere

7. The component of air used by green plants to make their food, is………………….

Ans: Carbon dioxide.

Chapter 16

Do  Ques Ans

Class 7 NCERT Ques ans

 Chapter 1 "Nutrition in Plants" 

Q.1. Why do organisms need to take food?

Ans:- All organisms require energy for their life processes . Plants prepare their food and acquire nutrients from abiotic components like soil, air , water and sunlight. On the other hand animals need to get food from either plants or other animals to obtain nutrients. Hence animals need to take food to acquire nutrients and energy.

Q.2. Distinguish between a parasite and a saprotroph.

Ans:- 

Parasite:- Organisms which live either in or on the host body is called parasite.

Example :- lice, liver fluke.

Saprotroph:- Organisms which take their nutrients from dead and decaying matter. 

Example :- Fungi.

Q.3. How would you test the presence of starch in leaves?

Ans. The presence of starch in leaves can be tested by Iodine test. When we remove chlorophyll from leaf by boiling it in alcohol and then put 2 drops of iodine solution, its colour change to blue indicates the presence of starch.

Q.4. Give a brief description of the process of synthesis of food in green plants.

Ans. The green plants have chlorophyll in the leaves. The leaves use C02 and water to make food in presence of sunlight.

 Carbon dioxide + water (in the presence of sunlight and chlorophyll) ---> Glucose + Oxygen .

Q.5. Show with the help of a sketch that the plants are the ultimate source of food.

Chapter 2 Nutrition in animals

Q.5. What are villi? What is their location and function?
Ans. The finger like projections in the inner walls of the small intestine is called villi. These are found in small intestine.
Function: The villi increase the surface area for absorption of the digested food

Q.6. Where is the bile produced? Which component of the food does it help to digest?
Ans. Bile is produced in liver. The bile juice stored in sac called the gall bladder. It helps in the digestion of fats.

Q.7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Ans. Cellulose is the carbohydrate that can be digested by ruminants. Ruminants have large sac like structure between the small intestine and large intestine. The cellulose of the food is digested by the action of certain bacteria which are not present in humans.

Q.8. Why do we get instant energy from glucose?
Ans. Because it easily breaks down in the cell with the help of oxygen which provides instant energy to the organism. Glucose does not need digestion, it is directly absorbed into the blood.

10. Write one similarity and one difference between the nutrition in amoeba and human beings.
Ans. Similarity: The digestive juices in amoeba are secreted into food vacuole and in human beings the digestive juices are secreted in stomach and small intestine. Then the juices convert complex food into simpler soluble and absorbable substances. 

Difference: Amoeba captures the food with help of pseudopodia and engulf it. In human beings food is taken by the mouth

Q.13. Can we survive only on raw, leafy vegetables/grass? Discuss.
Ans. We know that the animals, fungi, bacteria, non-green plants and human being do not have the ability to make their own food. They depend upon autotrophs for their food directly or indirectly. The green plant (leafy vegetables/grass) trap solar energy and make their own food in the form of glucose. So, we can say that leafy vegetables and grass can provide sufficient energy to help us survive.

Chapter 3 :- Fibre to Fabric 

Q.4. What is meant by the following terms?
(i) Rearing (ii) Shearing (iii) Sericulture

REELING:-The process of taking out threads from the cocoon fro use as silk is called reeling of silk.

SHEARING:-The fleece of sheep along with a thin layer of skin is removed from its body. This process is called shearing.

SERICULTURE:-Rearing of silkworms for obtaining silk is called sericulture.

Q.6 Make sketches of the two stages in the life history of the silk moth which are directly related to the production of silk
Ans.

Chap 4 " Heat"

1. State similarities and differences between the laboratory thermometer and the clinical thermometer.
Ans. Similarities:

(i) Both thermometers consist of long narrow uniform glass tubes.
(ii) Both have a bulb at one end.
(iii) Both contain mercury in bulb.
(iv) Both use Celsius scale on the glass tube.

Differences:
(i) A clinical thermometer reads temperature 35°C to 42°C while the range of laboratory thermometer is -10°C to 110°C.

(ii) Clinical thermometer has a kink near the bulb while there is no kink in the laboratory thermometer.
Due to kink mercury does not fall down on its own in clinical thermometer.

.2. Give two examples each of conductors and insulators of heat.
Ans. Conductors—aluminium, iron Insulators—plastic, wood.

Q.5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing?

Ans.More layers of clothing keep us warm in winters as they have a lot of space between them. This space gets filled up with air. Air is a bad conductor, it does not allow the body heat to escape out.

Q.6. Look at figure 4.6. Mark where the heat is being transferred by conduction, by convection and by radiation

Q.7. In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Ans.In places of hot climate it is advised that the outer wall of houses be painted white because white colour reflects heat and the houses do not heat up too much

Chapter 5:- Acids , Bases and Salts 

Q.1:- State differences between acids and bases.

Ans:-Properties of acids :-

• Produce hydrogen ions [H+] ions in water.
• Sour taste
• Turn blue litmus red

Properties of base :- 

• Produce hydroxide ions [OH-] in water.
• Water soluble base are called alkalies.
• Bitter taste 

.3.Name the source from which litmus solution is obtained. What is the use of this solution?

Ans.Litmus solution is extracted from lichens. It is used to determine whether the given solution is acidic or basic.

.4.Is the distilled water acidic/basic/neutral? How would you verify it?

Ans.Distilled water will be neutral. We can verify it by showing that neither blue nor red litmus paper changes its colour when dipped in it.

Q.5.Describe the process of neutralisation with the help of an example.

Ans.The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.

Antacids like milk of magnesia (magnesium hydroxide), baking soda, etc. which contain a base are used for reducing acidity in stomach when excessive acid released by glands.

.7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are

not labelled. He has to serve the drinks on the demand of customers. One customer

wants acidic drink, another wants basic and third one wants neutral drink. How

will Dorji decide which drink is to be served to whom?

Ans.Dorji can decide with the help of litmus paper:

(i) The drink which would turn a red litmus blue would be basic.

(ii) If the drink turns a blue litmus to red would be acidic.

(iii) The drink which would not affect both red and blue litmus would be neutral.

Q.8.Explain why:

(a) An antacid tablet is taken when you suffer from acidity.

(b) Calamine solution is applied on the skin when an ant bites.

(c) Factory waste is neutralised before disposing it into the water bodies.

Ans.(a) We take an antacid such as milk of magnesia to neutralises the excessive acid released in stomach.

(b) Ant injects an acidic liquid (Formic acid) into the skin on biting which causes inflammation, to the skin. The effect of the acid can be neutralised by rubbing. Calamine solution which contains zinc carbonate which is very weak base and causes no harm to the skin.

(c) The wastes of factories contain acids. If acids are disposed off in the water body, the acids will harm the organisms. So factory wastes are neutralised by adding basic substances.

.9. Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

Ans.Name of the substances Effect on turmeric indicator

1. Hydrochloric acid Yellow to blue

2. Sodium hydroxide Yellow to red

3. Sugar solution No change

Q.10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Ans. (i) It can be identified on the basis of the following observations : Bases change the colour of litmus paper to blue. As the colour of blue litmus paper is not affected, the solution must be basic.

(ii) If the solution is neutral, even then colour of litmus will not change.

Chapter 6

 Q.4. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Ans. The reaction between baking soda and lemon juice can be given as below:

Lemon juice + Baking soda ————-> C02 (bubbles) + Other substances

(Citric acid)   +  (Sodium hydrogen carbonate) --> (Carbon dioxide)

It is a chemical change

Q.5. When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Ans. When a candle burns, both physical and chemical changes occur:

(i) Physical change: melting of wax, vapourisation of melted wax.

(ii) Chemical change: Burning of vapours of wax to give carbon dioxide, heat and light.

LPG is another example in which physical change occurs when LPG comes out of cylinder and is converted from liquid to gaseous state and a chemical change occurs when gas burns in air.

Q.6. How would you show that setting of a curd is a chemical change?

Ans. We can say that setting of curd is a chemical change because we can not get the original substance, i.e., milk back and a new substance is formed with different taste, smell and other chemical properties

.7. Explain why burning of wood and cutting it into small pieces are considered as two different types of changes. ~

Ans. Burning of wood is a chemical change because in burning new substances are formed as

Wood + Oxygen ———–> Charcoal + Carbon dioxide + Heat + Light

But cutting it into small pieces is physical change because no new substance is formed. We can only reduce the size of wood.

Q.8. Describe how crystals of copper sulphate are prepared.

Ans. Take a cupful of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling, add copper sulphate powder slowly. Continue to add copper sulphate powder till no more powder can be dissolved. .During this process continuously stir the solution. Filter the solution. Leave it for cooling. Look it after some time, you can see the crystals of copper sulphate

9. Explain how painting of an iron gate prevents it from rusting?

Ans. It is known that for rusting the presence of oxygen and moisture is essential. Painting prevents the iron gate from coming in contact with oxygen and moisture.

Q.10. Explain why rusting of iron objects is faster in coastal areas than in deserts.

Ans. As content of moisture in the air in coastal areas is higher than in the air in deserts. So, the process of rusting is faster in coastal areas.

Chapter 7 

Q.1.Name the elements that determine the weather of a place.

Ans. The temperature, humidity, rainfall, wind-speed, etc. are called the elements that determine the weather of a place.

Q.2. When are the maximum and minimum temperature likely to occur during the day?

Ans.The maximum temperature of the day occurs generally in the afternoon and the minimum temperature occurs in the early morning.

Q.7. The tropical rainforests has a large population of animals. Explain why it is so.

Ans. Because of continuous warmth and rain, the tropical region supports an enormous number and a wide variety of animals

Q.8.Explain with examples, why we find animals of certain kind living in particular climatic conditions.

Ans. Animals are adapted to survive in the conditions in which they live. 

Features and habits which help them to adapt to their surroundings are the result of evolution.

 So, to survive in a particular type of climate the animals must have certain adapted features.

 This is the reason we find animals of certain kind living in particular climatic conditions. 

For example, animals in the polar region are adapted to the extremely cold climate.

 They have special characteristics, such as white fur, strong sense of smell, a layer of fat under the skin, wide and large paws for swimming and walking in snow etc

Q.9. How do elephants living in the tropical rainforests adapt themselves?

Ans. The elephant has adapted to the conditions of rainforest in many remarkable ways. 

It has a trunk that it uses as a nose because of this it has a strong sense of smell.

 The trunk is also used by it for picking up food.

 Its tusks are modified teeth. 

These can tear the bark of trees that an elephant loves to eat. 

So, the elephant is able to handle the competition for food very well. 

Large ears of the elephant help it to hear even very soft sounds.

 They also help the elephant to keep cool in the hot and humid climate of the rainforest.

Chap 8

.2. Suggest two methods to find out wind direction at a given place.
Ans.(i) Take a piece of a paper in your hand. Allow it to fall from your hand. It will flow in the direction in which wind is blowing.
(ii) You can also use a wind-pane which helps us to know accurate wind direction.

Q.3.State two experiences that made you think that air exerts pressure.
Ans.(i) Balloons and balls can be used only when they are inflated with air. When balloon is overfilled with air it bursts due to excessive air pressure.
(ii) Compressed air is used in the brake system for stopping trains.

Q.4.You want to buy a house. Would you like to buy a house having windows but no ventilators? Explain your answer.
Ans.No, a house which has no ventilators is not a safe or healthy house to live in. The air circulation is not there in such a house. So, it has no fresh air. Because warm air rises up and goes out through ventilators and fresh air comes in through windows.

Q.5.Explain why holes are made in hanging banners and hoardings.
Ans.Air exerts pressure. Due to this pressure banners and hoarding flutter and torn when wind is blowing fast. Holes are made in banners and hoardings so that wind passes through the holes and they do not become loose and fall down.

Q.6.How will you help your neighbours in case cyclone approaches your village/town?
Ans. (i) I will make them aware of cyclone forecast and warning service.
(ii) Rapid communication of warning to the government agencies and all the important places.
(iii) Construction of cyclone shelters in the cyclone prone areas.
(iv) Helping them to shift essential goods, domestic animals etc. to safer places.

Q.7.What planning is required in advance to deal with the situation created by a cyclone?
Ans.To deal with cyclone, it is important to follow the following points :
(i) carefully listening the warnings transmitted on T.V. and radio.
(ii) moving to the safer places.
(iii) keeping an emergency kit ready.
(iv) store food in waterproof bags. .
(v) not venturing into sea.
(vi) keeping all the emergency numbers.

.8. Which one of the following places is unlikely to be affected by cyclone?
(i) Chennai (ii) Mangalore
(iii) Amritsar (iv) Puri
Ans.(iv) Amritsar

Q.9.Which of the statements given below is correct?
(i) In winter the winds flow from the land to the ocean.
(ii) In summer the winds flow from the land towards the ocean.

(iii) A cyclone is formed by a very high-pressure system with very high-speed winds revolving around it.

(iv) The coastline of India is not vulnerable to cyclones.
Ans.(i) In winter the winds flow from the land to the ocean.

Chapter 9 "Soil"

Q4. Explain how soil is formed.

Answer:Soil is formed through the process of weathering. Weathering is a process of physical breakdown and chemical decomposition of rocks and minerals near or at the surface of the earth. This physical and chemical decomposition is primarily done by wind, water, and climate. As a result of these processes, large rock pieces are converted into smaller pieces and eventually to soil.

Q5. How is clayey soil useful for crops?

Answer:

Following are the properties of clayey soil:

It has very good water holding capacity.

It is rich in organic matter.

For growing crops such as wheat, gram, and paddy, the soil that is good at retaining water and rich in organic matter is suitable. Therefore, clayey soils having these characteristics are useful for such kind of crops.

Q6. List the differences between clayey soil and sandy soil.

Answer:

Clayey Soil -

(i) It has much smaller particles

(ii) It can hold good amount of water.

(iii) It is fertile

(iv) Air content is low.

(v) Particles are tightly packed

(vi) Good for growing various crops.

Loamy Soil:-

(i) It has much larger particles.

(ii) It cannot hold water

(iii) It is not fertile

(iv) Air get trapped between the particles.

(v) Particles are loosely packed

(vi) Not suitable for growing crops.

Q8. Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.

Answer:

9. Explain how soil pollution and soil erosion could be prevented.

Answer:

Prevention of soil pollution:

The persistent build-up of toxic compounds in the soil is defined as soil pollution. To prevent soil pollution, its causes must be controlled.

Reduce the use of plastics: Plastics and polythene bags destroy the fertility of soil. Hence, these should be disposed off properly and if possible, their use should be avoided.

Industrial pollutants: Some waste products from industries and homes pollute soil. These pollutants should be treated chemically to make them harmless before they are disposed off.

Insecticides: Other pollutants of soil include pesticides and insecticides. Therefore, excessive use of these substances should be avoided.

Chapter 10 :- Respiration in organisms

Q1. Why does an athlete breathe faster and deeper than usual after finishing the race?

Answer:

During the run, the demand of energy is high but the supply of oxygen to produce energy is limited. Therefore, anaerobic respiration takes places in the muscle cells to fulfill the demand of energy. After finishing the race, an athlete breathe faster and deeper than usual so that more oxygen is supplied to the cells.

Q2. List the similarities and differences between aerobic and anaerobic respiration.

Answer:

Similarity:

(i) In both aerobic and anaerobic respiration, food is broken down to release energy.

(ii) Both takes place inside cells.

(iii) Both produces byproducts.

Differences:

Aerobic Respiration

(i) It takes place in the presence of oxygen.

(ii) Energy is released in higher amount.

(iii) Carbon dioxide and water are produced as byproducts.

(iv) It is a slow process.

(v) Examples: Animals and plants cells.

Anaerobic Respiration

(i) It takes place in the absence of oxygen.

(ii) Energy is released in lesser amount

(iii) Carbon dioxide and water are produced as byproducts.

(iv) It is a fast process.

(v) Examples: Human cells, yeast, Bacteria etc.

Q3. Why do we often sneeze when we inhale a lot of dust-laden air?

Answer:

We often sneeze when we inhale a lot of dust-laden air to expel out these foreign particles. These particles get past the hair in the nasal cavity and irritate the lining of the cavity which results in sneezing.

Q4. Take three test-tubes. Fill each of them with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO2 ?

Answer:

Test-tube A will have the highest concentration of CO2 because snail will take in oxygen and gives out CO2.

In test-tubes B and C, the CO2 will be utilized by the water plant for synthesizing food and hence there will be less concentration of CO2 in these.

Chapter 11 " Transportation in animals and plants"

Q.4.Why is transport of materials necessary in a plant or an animal? Explain.

Ans.Transport of materials is necessary for plants or animals because due to it the nutrients and oxygen are made available to all the parts of the body. If the transport of necessary nutrients and oxygen does not take place in the body, the body will not be able to survive.

Q.5.What will happen if there are no platelets in the blood?

Ans.The blood platelets are responsible for the clotting of the blood. When some injury occurs blood starts flowing. But it clots on its own. If there are no platelets, the blood will not be able to clot and keep on flowing. Huge loss of blood ultimately causes death.

Q.6.What are stomata? Give two junctions of stomata.

Ans.There are small openings on the lower surface of the leaves. These pores are called stomata. These openings are surrounded with guard cells.

Functions of stomata:

1. It helps in the transpiration of water, i.e., the loss of excess water from the plant.

2. Loss of water from the stomata creates an upward pull, i.e., suction pull which helps in absorption of water from the roots.

3. They help in exchange of gases.

Q.7.Does transpiration serve any useful function in plants? Explain.

Ans.(i) It helps to enhance the absorption of water and dissolved minerals by creation of a suction pull.

(ii) It helps in getting rid of the excess water.

(iii) It helps in transport of water and minerals to leaves and leaves use the water for photosynthesis. ‘

(iv)It produces a cooling effect on the plant

Q.8.What are the components of blood?

Ans.There are four components of blood:

(i) Plasma is a liquid part of blood which is yellowish in colour and contain 90% water. It contains food, enzymes, wastes and proteins etc

(ii) Red blood cells are disc shaped cells containing red coloured pigment called haemoglobin in it. Haemoglobin helps in transportation of oxygen.

(iii) White blood cells are the fighting cells which protect us against bacteria and foreign materials causing infections.

(iv) Platelets help in clotting of the blood

Q.9.Why is blood needed by all the parts of a body?

Ans. Blood is needed by all the parts because it contains the digested food and oxygen in it. It supplies the oxygen and digested food to various parts of the body to provide essential energy to them which helps the body to perform various functions

Q.10.What makes the blood look red?

Ans. A red pigment called haemoglobin gives the blood its red colour. This pigment helps in carrying oxygen to various parts of the body by blood

Q.11.Describe the function of the heart.

Ans. The right auricle and ventricle receive blood with carbon dioxide from all parts of the body. The collected blood is then pumped to the lungs for the purification. In lungs, the exchange of gases takes place and purified blood is sent back to left auricle. It pumps it to the left ventricle, which in turn pumps off the purified blood to all parts of body through arteries

Q.12.Why is it necessary to excrete waste products?

Ans. Certain waste and toxic products are formed during functioning of body cells. The waste products like urea etc. are toxic. When these toxic materials are not removed from the body, they get mixed with blood and can damage the cells of body. It is necessary to remove such poisonous waste materials from our body.

Q.13.Draw a diagram of the human excretory system and label the various parts.

Ans.

Chemical reactions and equations

 What we will study:-

- Chemical reactions

- Chemical equations

- Types of chemical reactions.

Why study chemical reactions?

Because it occurs in our day to day life.

For example:- Food left at room temperature during summer starts melting.( Because chemical reaction happen in food )

Medicines taken react in body and we feel better.

Trees derive it's food by photosynthesis that is nothing but chemical reactions.

We respire (food + oxygen--> energy)

Remote cells

Rusting of iron (Fe + O2 ---> rust)

Digestion of food

In vehicle, fuel burns and produces energy and heat.

Observations:- following observations helps us to determine whether a chemical reaction has taken place:-

• Change of state
• Change of colour
• Evolution of a gas
• Change of temperature.

Activity:-

• Clean a magnesium ribbon about 2 cm long by rubbing it with sand paper.
• Hold it with a pair of tong.
• Burn it using a spirit lamp or burner and collect the ash.

Observations:- 

• Magnesium ribbon burns with a dazzling white flame and changes into a white powder.
• Magnesium + Oxygen (heat ) -----> Magnesium oxide
• Mg(s) + O2 (g) ∆ ---> MgO (s)

Reactant :- The substances that undergo chemical change in the reaction.

Product :- The new substance, formed during the reaction is the product.

Mg + O2 are reactant and MgO is product.

Writing chemical equation:- 

Mg + O2 ∆ --> MgO

CO (g) + 2H2(g) (340 atm) --- > CH3OH (l)

6CO2 (aq) + 6H2O (l) [sunlight and chlorophyll] ----> C6H12O6 (aq) + 6O2(aq)

This is the reaction of photosynthesis.

States of chemicals (Reactants and Products) :-

aq -> aqueous solution (dissolved in water)

l -> liquid

s -> insoluble solid or precipitate

g -> gas

Balanced chemical equation:-

According to law of conservation of mass , mass can neither be created nor be destroyed in a chemical reaction. That means total mass of elements presents in products of a  chemical reaction has to be equal to total mass  of elements present in reactants.

Number of atoms of each element remains the same before and after a chemical reaction.

Example :-

2Mg + O2 ----> 2MgO

Zn + H2SO4 -----> ZnSO4 + H2

Balanced chemical equation:- Exercise:- Is the equation balanced?

Zn + H2SO4 ----> ZnSO4 + H2 

YES

Fe + H2O -----> Fe3O4 + H2

NO

CO (g) + H2 -----> CH3OH

NO

6CO2 + 6H2O (SUNLIGHT + CHLOROPHYLL) --> C6H12O6 + 6O2

YES

Balance a chemical equation:- rule:-

Priority :-

• Balance polyatomic (if exist in both reactants and products)
• Balance metals 
• Balance non metals (hydrogen and oxygen at last)
• No fraction should exist in final equation.
• Note:- formula should not be changed.

Exercise :- Balance it

1. N2 + H2 --> NH3

Balanced :- N2 + 3H2 ---> 2NH3

2. CH4  + O2 --> H2O + CO2

Balanced :- CH4 + 2O2 ---> 2H2O + CO2 

3. C4H10 + O2 --> CO2 + H2O 

Balanced:- 2C4H10 + 13O2 --> 8CO2 + 10H2O

4. AgNO3 + MgCl2 --> AgCl + Mg(NO3)2

Balanced:- 2AgNO3 + MgCl2 ---> 2AgCl + Mg(NO3)2

5. K(ClO3) + KCl ---> KCl + O2

Balanced:- 2K(ClO3) + 2KCl ---> 4KCl + 3O2

6. HNO3 + Ca(OH)2 ---> Ca(NO3)2+ H2O

Balanced:- 2HNO3 + Ca(OH)2 ---> Ca(NO3)2+ 2H2O

7. NaOH + H2SO4 ---> Na2SO4 +H2O

Balanced:- 2NaOH + H2SO4 ---> Na2SO4 + 2H2O

8. NaCl + AgNO3 --> AgCl + NaNO3

Balanced:- NaCl + AgNO3 --> AgCl + NaNO3

9. BaCl2 + H2SO4 ---> BaSO4 +HCl

Balanced:- BaCl2 + H2SO4 ---> BaSO4 +2HCl

10. H2SO4 + KOH ---> K2SO4 + H2O

Balanced:- H2SO4 + 2KOH ---> K2SO4 + 2H2O

11.H3(PO4) + Ca(OH)2 ---> H2O + Ca(PO4)2

Balanced:- 2H3(PO4) + 3Ca(OH)2 ---> 6H2O + Ca(PO4)2

Now write balance chemical equation for:-

1. Hydrogen + Chlorine -->  Hydrogen chloride

S.Eq :- H2 + Cl2 --> HCl

B.Ch. Eq:- H2 + Cl2 --> 2HCl

2. Barium chloride + Aluminium sulphate ----> Barium sulphate + Aluminium chloride 

S.Eq:- BaCl2 + Al2(SO4)3 ---> BaSO4 + AlCl3

B. Ch. Eq:- 3BaCl2 + Al2(SO4)3 ---> 3BaSO4 + 2AlCl3

3. Barium chloride + potassium sulphate ---> Barium sulphate + potassium chloride

S. Eq:- BaCl2 + K2SO4 ---> BaSO4 + KCl 

B. Ch. Eq - BaCl2 + K2SO4 --> BaSO4 + 2KCl

4. Calcium hydroxide + Carbon dioxide --> calcium carbonate + water

S.eq:- Ca(OH)2 + CO2 ---> CaCO3 + H2O

B. Ch. Eq:- Ca(OH)2 + CO2 ---> CaCO3 + H2O

5. Zinc + Silver nitrate ---> Zinc nitrate + Silver

S.eq:- Zn + AgNO3 ---> Zn(NO3)2 + Ag

B. Ch. Eq:- Zn + 2AgNO3 ---> Zn(NO3)2 + 2Ag

6. Aluminium + Copper chloride --> Aluminium chloride + copper

S.eq:- Al + CuCl2 --> AlCl3 + Cu

B.ch. eq.:- 2Al + 3CuCl2 --> 2AlCl3 + 3Cu

Write a balanced chemical equation with state symbols for following reactions:- 

1. Sodium hydroxide (in water) reacts with Hydrochloric acid (in water) to produce sodium chloride solution and water.

S.eq:- NaOH (l) + HCl (l) ---> NaCl (aq) + H2O

B.ch. eq:- NaOH (l) + HCl (l) ---> NaCl (aq) + H2O

2. Solutions of Barium Chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride 

S.eq:- BaCl2(aq) + Na2SO4 (aq)---> BaSO4 (s) + NaCl(aq)

B.ch.eq:- BaCl2(aq) + Na2SO4 (aq)---> BaSO4 (s) + 2NaCl(aq)

Type of chemical reaction:-

1. Combination reaction

2. Decomposition reaction

3. Displacement reaction

4. Double displacement reaction

5. Combustion reaction

Other types of chemical reaction:-

1. Redox reaction

2. Acid base reaction (neutralisation reaction)

3. Acid metal reaction

4. Exothermic and endothermic reaction

5. Precipitation reaction

6. Catalysis reaction

7. Biochemical (enzyme) reaction

8. Organic chemistry reactions

9. Photochemical reaction (light)

10. Solid state reactions

11. Corrosion reaction

12. Rancidification reaction.

Note:- other types of reactions are involved in above 5 types.

Combination / synthesis chemical reaction:- 

General form :- A + B --> AB

Description:- Two chemical species combine to produce a single compound.

Example:- Quick lime +  water --> slaked lime

CaO(s) + H2O(l) --> Ca(OH)2 (aq)

Hydrogen + Oxygen --> Water

2H2(g) + O2(g) --> 2H2O (l)

Sodium + Chlorine --. Sodium chloride

2Na(s) + Cl2(g) --> 2NaCl (s)

Magnesium + Oxygen --> Magnesium oxide

2 Mg (s) + O2(g) --> MgO (s)

Carbon monoxide + Oxygen ---> Carbon dioxide

2CO (g) + O2(g) --> 2CO2

Sulphur dioxide + Oxygen --> Sulphur trioxide

2SO2 (g) + O2(g) ---> 2SO3(g)

Activity:-

Take a small amount of CaO in a Beaker.

Slowly add water to this.

Beaker gets hot.

CaO + H2O --> Ca(OH)2 + heat

Two substances combine to form product.

Decomposition chemical reaction:- 

General form:- AB --> A + B 

Description :- A single compound decomposes to produce two or more chemical species.

Example:- 

1. Water --> Hydrogen + oxygen 

2H2O(l) ---> 2H2(g) + O2(g)

2. Hydrogen peroxide ----> water + oxygen

2H2O2 (aq) --> 2H2O(l) + O2(g)

3. Copper carbonate --> copper oxide + Carbon dioxide

CuCO3 (s) --> CuO(s) + CO2(g)

4. Ammonia ---> Nitrogen + Hydrogen

2NH3(g) ---> N2(g) + 3H2(g)

5. Nitrogen triiodide --> Nitrogen + Iodine

2NI3 (s) --> N2(g) + 3I2(s)

Activity:-

Take about 2 gram ferrous sulphate crystals in a dry boiling tube.

Note the colour of the ferrous sulphate crystals.(greenish blue)

Heat the boiling tube over the flame of a burner.

Observe the colour of crystals (red) after heating and pungent smell.

2FeSO4 (s)[ferrous sulphate] ---> Fe2O3(s)[ferric oxide]+ SO2(g) +SO3(g)

Activity 2:- 

Take about 2g silver chloride in a dish and note the colour.

Place this dish in sunlight for some time 

Observe the colour of silver chloride after some time.

2AgCl (s) [in the presence of sunlight] ---> 2Ag(s) + Cl2

Displacement chemical reaction:- 

General form:- AB + C --> CB + A

Description :- An element displaces another element from its compound.

Example:- 

1.Hydrochloric acid + Magnesium ---. Magnesium chloride + hydrogen

2HCl + Mg ---> MgCl2 + H2

2. Sulphuric acid + iron ---> Iron sulphate + Hydrogen

H2SO4 (aq) + Fe(s) ---> FeSO4(aq) + H2(g)

3. Nitric acid + Magnesium --> Magnesium nitrate + hydrogen

2HNO3 + Mg --> Mg(NO3)2 + H2

4. Zinc + hydrochloric acid ---> zinc chloride + hydrogen

Zn(s) + 2HCl (aq) --> ZnCl2(aq) + H2(g)

5. Lead + Sulphuric acid --> Lead sulphate + Hydrogen

Pb(s) + H2SO4 (aq) ---> PbSO4 + H2(g)

Activity:- 

Take 2 iron nails and two test tubes marked as A and B.

In each test tube , take about 10mL copper sulphate solution.

Immense one nail in copper sulphate solution in test tube B for about 20 minutes.

After 20 mins, take out the iron nails from copper sulphate solution.

Compare the intensity of blue colour of CuSO4 solution in test tubes.

Also , compare the colour of iron nail dipped in copper sulphate solution with one kept aside.

Fe(s) + CuSO4(aq) --> FeSO4 (aq) + Cu(s)

Double displacement chemical reaction:- 

General form:- AB + CD ---> AD + CB

Description:- Two different atoms or group of atoms are exchanged in double displacement reaction.

Example :- precipitation and acid base reaction

1. HCl(aq) +NaOH (aq) --> NaCl (aq) + H2O(l)

2. AgNO3 (aq) + NaCl (aq) ---> AgCl + NaNO3(aq)

3. Ba(OH)2 + 2Cu(CNS) ---> Ba(CNS)2 + Cu(OH)2

4. FeS + HCl --> FeCl2 + H2S

Activity:- 

Take about 3 mL sodium sulphate solution in a test tube.

In another test tube, take about 3mL of barium Chloride solution.

Mix the two solutions

Observations:-  NaCl precipitate out.

Reaction:- Na2SO4 (aq) + BaCl2 (aq) ---> BaSO4 (s) + 2NaCl(aq)

Combustion Chemical reaction:-

C +O2 ---> CO2 + H2

Precipitation chemical reaction:-

General form:-

Solution A + Solution B ---> Insoluble solid C + Solution D

Description:- In a precipitation reaction two solutions are mixed together to produce an insoluble solid which is called the precipitate.

It is a type of double displacement reaction:-

Solubility :- Two solutions can be:-

- Soluble ( Milk + water)

- Moderately Soluble (NaCl + H2O)

- Insoluble [ sand + water]

Solubility is a Physical property of a pure substance . many observations over time have led to some rules about solubility of certain salts. 

1. Solubility is dependent on temperature. The solubility of most, but not all salts increases as temperature increases.

Example:- Potassium nitrate has a solubility of 31.2g per 100g of water at 20°C.

A solution that contains the maximum amount of a dissolved solute is said to be saturated.

As it cools , the Solution can no longer hold as much salt so excess amount separates as solid.

If the solution is cooled slowly enough the solid separates as crystals. The process of recrystallization is used to purify substances.

Neutralisation (Acid - Base) chemical reaction :-

 General form:- Acid + Base --> salt + water.

Description:- Reactants are a base and an acid and water. The positive charge of the hydrogen ion of acid and negative charge of the hydroxyl group lose their electric charge and become covalent molecules of water.

It is a type of double displacement reaction generally.

Example:- HCl + NaOH --> NaCl + H2O

Exothermic and endothermic chemical reaction:- 

Reactions in which heat is given out along with the products are called exothermic reactions.

Reactions in which energy is absorbed are known as endothermic reactions.

Example:- Mg  + O2 + heat---> MgO (endothermic reaction)

CaO + CO2 --> CaCO3 + heat (exothermic reaction)

Why is respiration considered as an exothermic reaction? Explain.

Because food we eat combines with oxygen present in atmosphere to produce energy and heat . Since heat is given out . So the reaction is exothermic.

Food + O2 --> energy + heat.

Redox reaction :- Oxidation and Reduction : Reaction that involves gain or loss of oxygen or hydrogen by substances is called redox reaction.

Oxidation is the gain of oxygen or loss of hydrogen.

Reduction is the loss of oxygen or gain of hydrogen.

2Cu + O2 + heat ---> 2CuO

Copper is oxidised

CuO + H2+ heat --> Cu + H2O 

Copper is reduced and hydrogen is oxidised.

Corrosion:- redox reaction in daily life.

When a metal is attacked by substances around it such as moisture, acid etc. It is said to corrode and the process is called corrosion. 

Example:- black coating on silver

Green coating on copper

Rusting of iron (4Fe + 3O2 --> 2Fe2O3)

Methods to prevent corrosion:-

By applying paints

By oiling

By electroplating

Rancidification:- Redox reaction in daily life :- 

When fats and oils are oxidised, they become rancid and their smell and taste change.

Method to prevent rancidification:-

Keeping food in air tight containers help to slow down oxidation.

Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.

By preserve it in fridge.

Surface chemistry and catalyst MSc 1sem

 Surface chemistry MSc previous

Introduction

• Residual unbalanced forces exist on the surface of solid.
•  As a result of these residual forces, the surface of solid has a tendency to attract and retain molecules of other species with which it is brought into contact.
•  As these molecules remain only at the surface, their concentration is more at the surface than in the bulk of the solid is known as adsorption.
• Solids when finely divided have a large surface area shows adsorption to a large extent.
• Solid that takes up a gas or vapour or a solute from a solution is called the adsorbent while the gas or vapour or the solute, which is held to the surface of the solid is called adsorbate.
• Collides such as charcoal, silica gel, alumina gel, clay, etc. Are good adsorbents. 
• Reason:- this is because they have extremely small dimensions, possess enormous surface area per unit mass .

Differentiate between adsorption and absorption :-

• 1. Adsorption is a surface phenomenon ,i.e. , it occurs only at the surface of the adsorbent.
• Where as absorption is a bulk phenomenon, i.e. , occurs throughout the body of the material.
• 2. In adsorption, the concentration on the surface of adsorbent is different from that in the bulk.
• Where as in absorption, the concentration is same throughout the material.
• 3.Rate of adsorption is high in the beginning and then decreases till equilibrium is attained.
• Whereas rate of absorption remain throughout the process.

Absorption implies that a substance is uniformly distributed throughout the body of a solid or a liquid.

Example :- water vapours are absorbed by anhydrous calcium chloride.

 Water vapour are adsorbed by charcoal.

 When a hot crucible is cooled in atmosphere, a film of moisture collects at its surface.  (Adsorption of water vapour on the material of the crucible)

Charcoal when mixed with a coloured solution of sugar, adsorbs the colouring matter and is used as a decoloriser. 

Sorption :- a process in which both adsorption and absorption take place simultaneously.

Type of adsorption :- Two types 

1. Physical adsorption (physisorption)

2. Chemical adsorption (chemisorption) 

Physisorption :- When a gas is adsorbed on the surface of a solid by van Der Waals forces without resulting into the formation of any chemical bond between the adsorbate and the adsorbent, it is called physical adsorption or van Der waals adsorption or physisorption.

Chemisorption:- Chemical process involving chemical interaction between the surface atoms of the adsorbent and the atoms of the adsorbate.

Example :- Oxygen is chemisorbed by carbon ;

Hydrogen is chemisorbed by nickel under suitable conditions.

In each case, a stable surface compound is formed called surface complex.

Differentiate between chemisorption  and physisorption :-

• Physisorption occurs only at very low temperature falling below the boiling point of the adsorbate. Chemisorption can occur at all temperature.
• Magnitude of chemisorption increase with rise in temperature.
• Magnitude of physisorption decrease with rise in temperature.
• Heat evolved in chemisorption is very high varying generally between 40-400 KJ /mol.
• Heat evolved in physisorption is quite low, varying generally between 4 - 40 KJ / mol.
• Chemisorption is irreversible as the gas adsorbed cannot be recovered from the adsorbent as such on lowering the pressure of the system at the same temperature. 
• Physisorption is reversible as the gas adsorbed can be recovered from the adsorbent easily on lowering the pressure of the system at the same temperature.
• Chemisorption operate within short distances only and does not extend beyond a monolayer of gas molecules or atoms on the surface of the solid. 
• Physisorption may extend beyond a monolayer also.
• In chemisorption, the adsorbate molecules are held by comparatively strong Valence forces. Hence the activation energy of desorption is very high.
• In physisorption, the adsorbate molecules are held by comparatively weak van Der Waals forces. Hence , the activation energy of desorption, in physisorption  is very low. 

Applications of adsorption:-

1. A very good method of creating a high vacuum is to connect a bulb of charcoal cooled in liquid air to a vessel which has already been exhausted as far as possible by a vacuum pump. 

Since the magnitude of adsorption at such a low temperature is quite high, the remaining trace of air , in spite of the low pressure, are adsorbed by the charcoal almost completely.

2. Activated charcoal is used in gas masks in which all toxic gases and vapours are adsorbed by the charcoal while pure air passes through its pores practically unchanged .

3. Silica and alumina gels are used as adsorbent for removing moisture and for controlling humidity of rooms.

4. Animal charcoal is used as a decoloriser in the manufacture of cane sugar.

5. Soil contains small amounts of colloidal fractions in the form of very fine particles of clay. It can always adsorb and retain certain amount of moisture in which nutrients, such as compounds of nitrogen, phosphorus and potassium can dissolve and pass up to the plant through the roots.

6. Adsorption also plays an important role in heterogeneous catalysis .

 Example:- role of finely divided iron in the manufacture of ammonia and that of finely divided nickel in the hydrogenation of oil.

Adsorption of gases by solids:- Several methods for determining adsorption of gases on solid adsorbents under the given conditions have been devised .

In one such method , the gas is contained in a vessel of known volume at a given temperature. 

The pressure of the gas is measured on a manometer attached to the vessel. 

The adsorbent is then introduced into the vessel by a suitable device.

Adsorption takes fairly quickly and the pressure of the gas falls . 

This is noted on the manometer.

Knowing the fall of pressure, the quantity of the gas adsorbed by the solid can be calculated, assuming Boyle's law to hold good.

It is necessary to apply correction due to the volume of the adsorbent added.