POLYATOMIC IONS

POLY-ATOMIC IONS

Ions that contained atoms of more than one element is known as poly-atomic ions.

Polyatomic ions are ions that are composed of two or more atoms that are covalently bonded together, and they carry an overall electric charge. These ions can be either positively or negatively charged, and they play an important role in chemistry and biochemistry.

Some examples of commonly encountered polyatomic ions include sulfate (SO₄^-2), nitrate (NO₃^-), carbonate (CO₃^-2), ammonium (NH₄⁺), and phosphate (PO₄^-3).

Polyatomic ions are often involved in chemical reactions, where they act as reactants, products, or catalysts. For example, sulfate is often used as a reactant in the production of fertilizers, while phosphate is a key component of DNA and ATP (adenosine triphosphate), which is the primary energy source for most biological processes.

Polyatomic ions are also important in the context of acid-base chemistry, as they can act as either acids or bases depending on the situation. For example, nitrate can act as a base in the presence of a strong acid, while ammonium can act as an acid in the presence of a strong base.

Overall, polyatomic ions play an important role in many areas of chemistry and biology, and a good understanding of their properties and behaviors is essential for anyone studying these subjects.

NAME	SYMBOLS	VALENCY
HYDROXIDE	OH	-1
ACETATE	CH₃COO	-1
CYANIDE	CN	-1
CHLORATE	ClO3	-1
CHLORITE	ClO2	-1
NITRATE	NO3	-1
NITRITE	NO2	-1
SULPHATE	SO4	-2
SULPHITE	SO3	-2
PHOSPHATE	PO4	-3
PHOSPHITE	PO3	-3
PERMANGANATE	MnO4	-1
HYDROGEN CARBONATE	HCO3	-1
CARBONATE	CO3	-2
SILICATE	SiO3	-2
CHROMATE	CrO4	-2
DICHROMATE	Cr2O7	-2
AMMONIUM	NH4	+1

Examples of Compounds having hydroxide (OH) ions

 

Compound Name	Formula	Uses
Sodium Hydroxide	NaOH	It is also called Caustic Soda. Used in manufacturing of paper, textiles, soaps etc.
Potassium Hydroxide	KOH	Used in the manufacturing of soaps and detergents.
Calcium Hydroxide	Ca(OH)2	It is also called Slaked Lime. Used as a construction materials.
Aluminium Hydroxide	Al(OH)3	Used in Antacid to neutralize acidity in stomach and treat ulcers.
Magnesium Hydroxide	Mg(OH)2	Used in Antacid to neutralize acidity and indigestion, heartburn.
Ammonium Hydroxide	NH4OH	Used in as Cleaning agent.
Barium Hydroxide	Ba(OH)2	Used in the production of Lubricants.

 

Examples of Compounds having Acetate (CH₃COO) ions

 

Compound Name	Formula	Uses
Sodium Acetate	CH3COONa
Acetic Acid	CH3COOH

 

Examples of Compounds having Cyanide (CN) ions

 

Compound Name	Formula	Uses
Potassium Cyanide	KCN
Hydrogen Cyanide	HCN

 

Examples of Compounds having Chlorate (ClO₃) ions

 

Compound Name	Formula	Uses
Potassium Chlorate	KClO3
Barium  Chlorate	Ba(ClO3)2
Calcium Chlorate	Ca(ClO3)2
Iron(III) Chlorate	Fe(ClO3)3
Zinc Chlorate	Zn(ClO3)

EXAMPLE: SOME COMMON COMPOUNDS CONTAINING HYDROXIDE IONS

Sodium Hydroxide NaOH

Potassium Hydroxide KOH

Calcium Hydroxide Ca(OH)₂

Aluminium Hydroxide Al(OH)₃

Acetate      (CH₃COO) (-1)

Sodium Acetate CH₃COONa

Cyanide.  (CN) (-1)

Potassium Cyanide KCN

Hydrogen Cyanide HCN

Chlorate (ClO₃) (-1)

Potassium Chlorate KClO₃

Chlorite (ClO₂) (-1)

Nitrate.    (NO₃) (-1)

Nitric Acid HNO₃

Potassium Nitrate KNO₃

Sodium Nitrate NaNO₃

Nitrite.     (NO₂) (-1)

Nitrous Acid HNO₂

Sulphate (SO₄) (-2)

Sodium Sulphate Na₂SO₄

Barium Sulphate BaSO₄

Zinc Sulphate ZnSO₄

Copper Sulphate CuSO₄

Sulphite.  (SO₃) (-2)

Phosphate (PO₄) (-3)

Phosphite. (PO₃) (-3)

Permanganate (MnO₄) (-1)

Hydrogen Carbonate (HCO₃) (-1)

Carbonate (CO₃) (-2)

Silicate (SiO₃) (-2)

Chromate (CrO₄) (-2)

Dichromate (Cr₂O₇) (-2)

Aluminate (AlO₃) (-3)

Ammonium (NH₄) (+1)

LECTURE 2: CHEMICAL EQUATIONS (CLASS X)

CHEMICAL EQUATIONS

The method of representing a chemical reaction with the help of symbols and formula of the substances involved in it, is known as a chemical equation. 

REACTANTS

The substances which take part in a chemical reaction are called reactants. 

The reactants are always written on the left hand side in an equation with a plus sign (+) between them. 

PRODUCTS

The new substances produced as a result of chemical reaction are called products. 

The products are always written on the right hand side in an equation with a plus sign (+) between them.

The arrow sign (→) is put in between the reactants and the products and always directed from left to right. 

A chemical equation is a short-hand method to represent a chemical reaction. 

TWO WAYS TO WRITE A CHEMICAL EQUATION

1. UNBALANCED CHEMICAL EQUATIONS. 

2. BALANCED CHEMICAL EQUATIONS. 

UNBALANCED CHEMICAL EQUATIONS

An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. 

Example:  H₂ + O₂ → H₂O

H atoms in Reactants = 2, in Products = 2

O atoms in Reactants = 2, in Products = 1

BALANCED CHEMICAL EQUATIONS

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. 

Example: Zn + H₂SO₄ → ZnSO₄ + H₂

Zn atoms in Reactants = 1, in Products = 1

H atoms in Reactants = 2, in Products = 2

S atoms in Reactants = 1, in Products = 1

O atoms in Reactants = 4, in Products = 4

BALANCING OF CHEMICAL EQUATIONS

The process of making the number of different types of atoms equal on both the sides of an equation is called balancing of chemical equation. 

(Steps are to be discussed in the class)

How to make a chemical equation more informative?

The chemical equation can be made more informative in three ways.

1. By indicating the physical states of the reactants and products.

2. By indicating the heat changes taking place in the reaction.

3. By indicating the conditions under which the reaction takes place. 

1. To indicate the Physical States of the Reactants and Products in an Equation.

We write 

For solids (s) , 

for liquids (l), 

for gas (g), 

for water solution or dilute (aq), 

for evolving gas ↑, 

for precipitates (insoluble solid product) ↓, 

Like 

Zn (s) + H₂SO₄(aq) → ZnSO₄ (aq) + H₂ (g) ↑

2. To indicate the heat changes in an equation

EXOTHERMIC REACTION

Those reactions in which heat is evolved are known as Exothermic Reactions.

Q. When calcium hydroxide reacts with carbon dioxide, white calcium carbonate precipitates and hydrogen gas evolved. Write the chemical reaction.

Ans. Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s)↓ + H₂O (l)

Q. What happens when we burn Methane ? Write its chemical reaction. 

Ans. When Methane (natural gas) burns in the presence of Oxygen from air, Carbon Dioxide and Water is formed along with a large quantity of heat. 

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (l) + Heat energy

Burning of natural gas is an exothermic reaction. Infact, all combustion (burning) is exothermic reaction. 

Q. What happens when respiration takes place?

Ans. When glucose undergoes a slow combustion by combining with oxygen in our cells to produce energy in a process called respiration, carbon dioxide along with water and Energy is produced. 

C₆H₁₂O₆ (aq) + 6O₂ (g) → 6CO₂ (g) + 6H₂O (l) + Enegy

Hence, Respiration is aalso an Exothermic process as energy is produced during the reaction. 

Q. Write the chemical equation of burning of Magnesium wire in air. Is it an exothermic process?

Ans. When Magnesium wire burns in wire, Magnesium Oxide is produced along with heat and light energy. Hence, it is an exothermic reaction. 

2Mg (s) + O₂(g) → 2MgO (s) + Heat Energy + Light Energy

Q. Fill in the blanks

Decomposition of vegetables into  compost is an example of ___________ reaction.

Ans. Exothermic

ENDOTHERMIC REACTION

Those reactions in which heat is absorbed are known as Endothermic reactions. 

Q. What happens when Nitrogen and Oxygen are heated to a very high temperature? What type of reaction it is?

Ans. When Nitrogen and Oxygen are heated to a very high temperature it forms Nitrogen monoxide which is an endothermic reaction. 

N₂ (g) + O₂ (g) → 2NO (g)

"All the decomposition reactions are endothermic as they need energy to start the reaction"

(i). Like the decomposition of Calcium Carbonate is an endothermic reaction. 

(ii). Photosynthesis is also an endothermic reaction. 

(iii). Electrolysis of water to form hydrogen and oxygen is also a decomposition reaction. 

3. To indicate the conditions under which the reaction takes place. 

{If heat is required for a reaction to take place, then the heat sign delta (Δ) is put over the arrow of the equation. If the reaction takes place in the presence of a catalyst than the symbol or formula of the catalyst is also written above or below the arrow sign in the equation.}

1. When potassium chlorate (KClO₃) is heated in the presence of manganese dioxide (MnO₂) catalyst, it decomposes to form potassium chloride (KCl) and oxygen (O₂) gas.

2. Methanol (CH₃OH) is manufactured from carbon monoxide (CO) and hydrogen (H₂) under extreme pressure (300 atm) and temperature (300°C) and in the presence of ZnO + CrO₃

3. In photosynthesis, glucose is formed from Carbon Dioxide and Water under Sunlight and Chlorophyll as catalyst. 

Q. Convey the following information in the form of a balanced chemical equation:

On adding an aqueous solution of sodium hydroxide to an aqueous solution of copper sulphate copper hydroxide is precipitated and sodium sulphate remains in solution. 

Ans: NaOH (aq) + CuSO₄ (aq) ⟹ Cu(OH)₂ (s)↓ + Na₂SO₄ (aq)

It is an unbalanced equation. When balanced it becomes

2NaOH (aq) + CuSO₄ (aq) ⟹ Cu(OH)₂ (s)↓ + Na₂SO₄ (aq)

IRON OXIDES

There are two types of iron oxides. 

Iron (II) oxide FeO, and Iron (III) oxide Fe₂O₃

Iron (II) oxide FeO is known as Ferrous oxide.

Iron (III) oxide Fe₂O₃ is known as Ferric Oxide. 

Mixture of both the oxide is called Magnetic Iron Oxide (Fe₃O₄). 

Q. Write a balanced equation for the chemical reaction when heated iron metal reacts with steam to form iron (II, III) oxide and hydrogen. 

Ans. Fe (s) + H₂O (g) → Fe₃O₄ (s) + H₂ (g)

But it is an unbalanced equation, when balanced it becomes, 

3Fe (s) + 4H₂O (g) → Fe₃O₄ (s) + 4H₂ (g)

Q1. Translate the following statement into chemical equation and then balance the equation:

Hydrogen gas combines with nitrogen to form ammonia. 

Q2. Write the balanced chemical equation for the following reaction:

Sodium metal reacts with water to form sodium hydroxide and hydrogen. 

Q3. Write the balanced chemical equation for the following reaction:

(i) Aluminium reacts with copper chloride to form aluminium chloride and copper.

(ii) Aluminium hydroxide reacts with sulphuric acid to form Aluminium sulphate and water.

(iii) Manganese oxide reacts with hydrochloric acid to form manganese chloride, chlorine gas and water.

Q4. When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution. 

a. What do you think substance X is likely to be?

b. Name the substance which the yellow solid consists of. 

c. Which characteristic of chemical reactions is illustrated by this example?

d. Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation. 

Reference Solution Physics (LIGHT)

LECTURE 1: CHARACTERISTICS OF CHEMICAL REACTION (CLASS X)

CHEMICAL REACTIONS

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Chemical reactions are the processes in which new substances with new properties are formed. During a chemical reaction, atoms of one element do not change into those of another element. Only a rearrangement of atoms takes place in a chemical reaction. 

Example:

(i) When hydrogen combines with oxygen water is produced, which is different from hydrogen as well as oxygen, it is an example of chemical reaction.

(ii) The burning of magnesium in air to form magnesium oxide is an example of chemical reaction.

(iii) Souring of milk, Formation of curd from milk, Cooking of food, Digestion of food in our body, Process of respiration, Fermentation of grapes, Rusting of iron, Burning of fuels, Burning of candle wax, and Ripening of fruits are examples of chemical reactions. 

REACTANTS

The substances which take part in a chemical reaction are called reactants. 

PRODUCTS

The new substances produced as a result of chemical reaction are called products. 

CHARACTERISTICS OF CHEMICAL REACTION

The important characteristics of chemical reactions 

1. Evolution of a gas

When one of the products is a gas. 

Examples:

a. When zinc granules (Zn) reacts with dilute sulphuric acid (H₂SO₄) then zinc sulphate (ZnSO₄) and hydrogen gas (H₂) is produced. Here, hydrogen gas is evolved. 

b. When sodium carbonate Na₂CO₃ reacts with dilute hydrochloric acid HCl it produces carbon dioxide CO₂ gas. It is also an example of evolution of gas. 

2. Formation of a precipitate

When one of the products is insoluble in water.

a. When carbon-di-oxide CO₂ is passed through lime water CaO, Calcium Carbonate CaCO₃ is precipitated. 

b. When Potassium Iodide (KI) reacts with lead nitrate PbNO₃ then Potassium nitrate KNO₃ is formed which is insoluble in water hence precipitated. 

c. When Barium Chloride BaCl₂ reacts with sulphuric acid (H₂SO₄), white Barium Sulphate BaSO₄ is produced, which is insoluble in water and hence precipitated. 

3. Change in colour

When the products have different colours than that of the reactants. 

a. When citric acid mixed with purple coloured Potassium Permanganate, the solutions turned to be colourless. 

b. When sulphur di oxide gas reacts with acidified orange coloured potassium dichromate, the solution turned to be green. 

4. Change in temperature

Some chemical reactions are characterized by a change in temperature. For example, when quicklime (CaO) reacts with water, then slaked lime  Ca(OH)₂ is formed and a lot of heat energy is produced. Therefore, it is a chemical reaction which produces change in temperature. 

Exothermic Chemical Reaction 

The chemical reaction which produces heat when reaction occurs is called an exothermic chemical reaction. The temperature always increases during an exothermic chemical reactions.

Example: (i). CaO + H₂O → Ca(OH)₂ 

Quicklime reacts with water to produce slaked lime and heat

                 (ii). Zn + H₂SO₄ → ZnSO₄ + H₂

Zinc granules reacts with dilute sulphuric acid to produce zinc sulphate and hydrogen and heat. 

Endothermic Chemical Reaction

The chemical reactions which absorb heat during the reaction are called endothermic chemical reactions. 

Example: 

(i). N₂ + 3H₂ → 2NH₃

Nitrogen reacts with hydrogen to produce ammonia by absorbing heat from surrounding.

(ii). Ba(OH)₂ + NH₄Cl → BaCl₂ + NH₃ + H₂O

Barium hydroxide reacts with ammonium chloride to produce Barium chloride ammonia and water by absorbing heat from surrounding.

5. Change in state

Some chemical reactions are characterized by a change in state.

Example: When wax is burned, then water and carbon dioxide are formed. Thus, the combustion of wax is characterized by a change in state from solid to liquid and gas. 

LECTURE 3: LIFE PROCESSES: NUTRITION IN ANIMALS

CLASS X   |    SCIENCE    |    LIFE PROCESSES

      Notes prepared by Subhankar Karmakar

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SCIENCE: CLASS X: CBSE (CLASS NOTES)

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• CLASSIFICATION OF ANIMALS ON THE BASIS OF FOOD HABITS

All the animals can be divided into three groups on the basis of their food habits or eating habits. These are:

• 1. Herbivores
• 2. Carnivores
• 3. Omnivores

• HERBIVORES
• Animals which eat only plants are called herbivores. 
• They are also called Herbivorous animals. 
• Some of the examples are goat cow buffalo horse etc. 

• CARNIVORES
• Those animals which eat only other animals as food are called Carnivores. 
• They eat only the flesh or meat of other animals.
• They are meat eaters.
• They are also called Carnivorous animals. 

• OMNIVORES
• Those animals which eat both, plants and animals, are called omnivores.
• They are also called omnivorous animals.
• Omnivores are plant eaters as well as meet eaters. 
• Human beings,  dog, are omnivorous animals.

Ultimately it is the energy of the Sun which provides food for plants and animals (herbivores, carnivores and omnivores).

• DIFFERENT STEPS IN THE PROCESS OF NUTRITION IN ANIMALS

There are five main processes concerned with the use of food by animals. They are as follows. 

• 1. Ingestion
• 2. Digestion
• 3. Absorption
• 4. Assimilation
• 5. Egestion
• INGESTION

The process of taking food into the body is called ingestion. When we put food into our mouth with hands we are ingesting. 

• DIGESTION

The process in which the food containing large, insoluble molecules is broken down into small, water soluble molecules, which can be absorbed by the body is called digestion. Most animals use both physical like chewing, grinding in mouth and chemical methods like breaking the large molecules using digestive juices like enzymes for digesting. 

• ABSORPTION

The process in which the digested food passes through the intestinal wall into blood stream is called absorption. 

• ASSIMILATION

The process in which the absorbed food is taken in by body cells and used for energy, growth and repair, is called assimilation. 

• EGESTION

A part of the food animals consume remain undigested as they are insoluble in water. The process in which the undigested food is removed from the body is called egestion. 

• NUTRITION IN UNICELLULAR ORGANISMS
• Amoeba is a unicellular organism. It eats microscopic animals and plants as food. The mode of nutrition in Amoeba is holozoic. 
• The process of obtaining food by Amoeba is called Phagocytosis. 
• It also follows the five steps processes for nutrition. 

• INGESTION IN AMOEBA

As Amoeba has no mouth or a fixed place for intake of food, Amoeba injests food by using its Pseudopodia, which is a temporary finger-like projections on the surface of the body. 

When a food particle comes near Amoeba, the food is engulfed with a little surrounding water to form a food vacuole inside the Amoeba. This food vacuole can be considered to be a "temporary stomach" of Amoeba. 

• DIGESTION IN AMOEBA

In Amoeba, food is digested in the food vacuole by digestive enzymes. The enzymes from surrounding cytoplasm enter into the food vacuole and breakdown the food into small and soluble molecules by chemical reactions. Therefore digestion in Amoeba takes place inside the food vacuole due to which the food become soluble.

• ABSORPTION IN AMOEBA

The digested food present in the food vacuole of amoeba is absorb directly into the cytoplasm of amoeba cell by diffusion. Since Amoeba consists of only one small cell it does not required blood system to carry the digested food. The digested food just spreads out from the food vacuole into the whole Amoeba cell. After absorption of food the food vacuole disappears.

• ASSIMILATION IN AMOEBA

A part of the food absorbed in Amoeba cell is used to obtain energy through respiration. The remaining part of absorbed food is used to make the parts of amoeba cell which lead to the growth of amoeba. Thus on assimilating food Amoeba grows in size and then Amoeba can reproduce by dividing into two daughter cells. 

• EGESTION IN AMOEBA

Amoeba has no fixed place for removing the undigested part of food. When a considerable amount of undigested food collected inside amoeba, then it cell membrane suddenly ruptures at any place and the undigested food is thrown out of the body of amoeba. 

• PARAMECIUM

Paramecium is also a tiny unicellular animal which lives in water. Paramecium uses its hair like structures called Cilia to sweep the food particles from water and put them into its mouth. 

Unlike amoeba paramecium has a mouth and it has cilia all over its body. When the cilia present around the mouth region of paramecium move back and forth, they sweep the food particles present in water into the mouse a paramecium. This is egestion for paramecium. 

LECTURE 2: CLASS 10 : LIFE PROCESSES : PHOTOSYNTHESIS - I

CLASS X   |    SCIENCE    |    LIFE PROCESSES

      Notes prepared by Subhankar Karmakar

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SCIENCE: CLASS X: CBSE (CLASS NOTES)

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• NUTRITION IN PLANTS
• The process by which green plants make their own food like glucose from carbon di oxide and water by using sunlight energy in the presence of chlorophyll is called photosynthesis.
• Chlorophyll is present in the green coloured bodies called chloroplasts inside the plant cells. 
• The leaves of a plant are green because they contain tiny green coloured organelles called Chloroplasts. 
• The process of photosynthesis
• The chemical reaction of the photosynthesis

6CO₂ + 6H₂O + Light energy (in the presence of chlorophyll) ⟹ C₆H₁₂O₆ + 6O₂

• PHOTOSYNTHESIS

Plants prepare their food (glucose) in the green leaves of the plant by combining carbon-di-oxide and water in the presence of sunlight and chlorophyll. The process is known as Photosynthesis.

• CHLOROPHYLL:

Chlorophyll is a green pigment found in the mesosomes of cyanobacteria and in the chloroplasts of algae and plants. It is needed for the process of photosynthesis.

• CARBON-DI-OXIDE

The plants derive carbon-di-oxide from the air by the plant leaves. Carbon-di-oxide enters the leaves through the small pores in them called stomata. 

• WATER

Water required for food preparation is taken from the soil through the roots. Water is transported to the leaves from the soil through the roots and stem. 

• SUNLIGHT

The sunlight provides the energy required to carry out the chemical reactions involved in the preparation of the food. The energy in the sunlight is absorbed with the help of chlorophyll. 

• Oxygen gas is produced as a by-product during the preparation of food by photosynthesis. This oxygen gas goes into the air. 
• The food prepared by the green leaves of a plant is in the form of a simple sugar called glucose. Glucose thus produced is sent to the different parts of the plant.
• The extra glucose is changed into another food called starch. This starch is stored in the leaves of the plant. Glucose and starch are called carbohydrates. 
• Green plants convert sunlight energy into chemical energy by making carbohydrates. 

• THE PHOTOSYNTHESIS PROCESS
• 1. Absorption of sunlight energy
• 2. Conversion of light energy into chemical energy and splitting of water into hydrogen and oxygen by light energy.
• 3. Reduction of carbon dioxide by hydrogen to form carbohydrate like glucose by utilising the chemical energy obtained by the transformation of light energy. 

• Conditions necessary for photosynthesis by green plants as well as autotrophic nutrition
• 1. Sunlight
• 2. Chlorophyll
• 3. Carbon dioxide
• 4. Water

A. Describe an experiment to show that Sunlight is necessary for photosynthesis

We know that green leaves make starch as food. As starch gives a black-blue colour with iodine solution. Plants store starch in their leaves. The green leaves of a plant are destarched by keeping this plant in a completely dark place in a room for atleast three days. 

• 1. We take a potted plant having Green leaves and place it in a completely dark place for about 3 days to destarch its leaves.
• 2. We take a thin strip of aluminium foil and wrap it in the centre of one leaf on both the sides. The covered part will not receive sunlight.
• 3. We keep this potted plant in bright sunshine for 3 to 4 days. 
• 4. We pluck the partially covered leaf from the plant and remove its Aluminium foil then immerse this leaf in boiling water for a few minutes. This will break down the cell membranes of leaf cells and make the leaf more permeable to iodine solution.
• 5. We put the plucked leaf in a beaker containing some alcohol. Place the beaker containing alcohol and leaf in a water bath and starts to heat it till the leaf becomes colourless. The boiling water will remove the chlorophyll from the green leaf. 
• 6. We remove the colourless leaf from alcohol, wash it in hot water and keep it in a petridish. We drop iodine solution on the leaf. 
• 7. The part which was wrapped in aluminium foil will not turn blue-black but rest of the parts of the leaf will become blue-black. 
• 8. Since the wrapped part didn't get sunlight, it did not produce starch. We can now conclude that 
• (i) sunlight is necessary for the process of photosynthesis.
• (ii) leaves make starch as food by photosynthesis.

• Variegated leaves:

The leaves which are partly green and partly white are called variegated leaves. The white part of the leaves doesn't contain chlorophyll. 

B. Describe an experiment to show that Chlorophyll is necessary for photosynthesis.

• 1. We take a potted plant having variegated leaves like a croton plant. The white part of the leaves doesn't contain chlorophyll whereas the green part contains chlorophyll. 
• 2. We place the plant in a completely dark place for about three days. 
• 3. We take out the plant and keep it under bright sun for 3 to 4 days 
• 4. We pluck the variegated leaf from the plant , boil it in water for few minutes, and then remove its green colour  chlorophyll by boiling in alcohol. The green part of the leaf  get decolourised.
• 5. We wash the decolourised leaf with hot water to soften and remove left-over Chlorophyll. 
• 6. We now pour iodine solution over the colourless leaf and observe the change in colour of the leaf. 
• 7. The inner part of leaf which was originally green turns blue black on adding iodine. 
• Chlorophyll is necessary for the process of photosynthesis to take place. 

C. Describe an experiment to show that Carbon Dioxide is necessary for photosynthesis.

• 1. We take a potted plant having narrow leaves and place it in a completely dark place for about three days to destarch its leaves. 
• 2. Take a glass bottle having a wide mouth and put some potassium hydroxide solution in it. 
• 3. Take a rubber cork which fits tightly into the mouth of the glass bottle and cut it into two halves. 
• 4. We put the destarched leaves in such a way, that upper half of the leaf should remain outside the glass bottle and only the lower half of the leaf should be inside the glass bottle.
• 5. The potted plant is kept in sunlight for 3 to 4 days. Upper half gets the carbon dioxide from air but lower half didn't get carbon dioxide as potassium hydroxide absorbed the carbon dioxide of the inside jar. 
• 6. We pluck the leaf and boiled it in alcohol then wash it with water.
• 7. We pour iodine solution over the colourless leaf. We observe that lower part of the leaf doesn't turned blue-black but the upper part became blue-black. 
• The photosynthesis to make starch in the leaf does not take place without carbon dioxide. 

Raw Materials for photosynthesis

The preparation of carbohydrates by plants by the process of photosynthesis requires two materials a. Carbon dioxide and b. Water

HOW THE PLANTS OBTAIN CARBON DIOXIDE

• STOMATA

There are large number of tiny pores called stomata on the surface of the leaves of plants. and green stem. The green plants take carbon dioxide from air for photosynthesis. The carbon dioxide gas enters the leaves of the plant through the stomata present on their surface. 

• STOMATAL PORES AND GUARD CELLS

STOMATAL PORES & GUARD CELL

• Each stomatal pore is surrounded by a pair of guard cells. The opening and closing of stomatal pore is controlled by the guard cells. 
• • When water flows into the guard cells, they swell, become curved and cause the pore to open. 
• • When guard cells lose water, they shrink, become straight and close the stomatal pore. 
• Plant losses water through the open stomatal pores hence when carbon dioxide is not needed by the plants, these pores are closed. 
• Oxygen gases produced during photosynthesis also goes out through the stomatal pores. 
• In most of the broad-leaved plants, stomata occur only on the lower surface of the leaf but in narrow-leaved plants, stomata are equally distributed on the both sides of the leaf. 
• Aquatic plants use the carbon dioxide gas dissolved in water for carrying out photosynthesis. 

HOW THE PLANTS OBTAIN WATER FOR PHOTOSYNTHESIS

• The water required by the plants for photosynthesis is absorbed by the roots of the plants from the soil through the process of osmosis. The water is absorbed by the roots of the plants is transported upward through the xylem vessels to the leaves. 
• Other nutrients like nitrogen, phosphorus, iron and magnesium etc. by the plants for its growth are taken by the plants from the soil through the roots of the plants. 

SITE OF PHOTOSYNTHESIS: CHLOROPLASTS

• Chloroplasts are the disc-like cell organelles of the photosynthetic cells of green plants which contain chlorophyll. At Chloroplasts photosynthesis take place. 
• The middle layer of the leaves are palisade layer and spongy layer and they contain photosynthetic cells which are called mesophyll cells. 
• Carbon dioxide enters through stomata and diffuses into the mesophyll cells and reaches the Chloroplasts. 
• Water is carried to the leaf by xylem and passes into the mesophyll cells by diffusion and reaches the Chloroplasts. 
• To reduce the water loss, there is a thin waxy protective layer called cuticle above and below a leaf. 

LECTURE 1 : CLASS XII: PHYSICS : ELECTRIC CHARGE & FIELD

CLASS XII   |    PHYSICS    |    ELECTRIC CHARGE

      Notes prepared by Subhankar Karmakar

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ELECTRIC CHARGE

Electric charge is an intrinsic property of elementary particles of matter which gives rise to electric force between various objects.

• Electric charge is a scalar quantity.
• SI unit of electric charge is coulomb (C).
• There are two types of charges- a. Positive charge and b. Negative charge.
• A proton has a positive charge (+e) and an electron has a negative charge (-e).
• Magnitude of charge of a proton and an electron are same.
• Charge of a proton = + 1.6 x 10⁻¹⁹ C
• Charge of an electron = - 1.6 x 10⁻¹⁹ C

POLARITY OF CHARGE

• The property which distinguishes the two kinds of charges is called the polarity of charge.

FUNDAMENTAL LAW OF ELECTROSTATICS: 

• Like charges repel and unlike charges attract each other.

• The charge developed on a glass rod when rubbed with silk is called positive charge.
• The charge developed on a plastic rod rubbed with wool is called negative charge. 

CONDUCTORS AND INSULATORS

• Conductors: The substances through which electric charges can flow easily are called conductors. 
• Insulators: the substances through which electric charges cannot flow easily are called insulators.
• When some charge is transferred to a conductor, it really gets distributed over his entire surface. 
• If some charge is put on an insulator, It stays at same place. 
• The process in which a body shares its charges with the earth is called grounding or earthing.

ELECTROSTATIC INDUCTION

• It is the phenomenon of temporary electrification of a conductor in which opposite charges appear at its closure and and similar charges appear at its further and in the presence of a nearby charged body. 
• When two conductors one or both are charged are in contact with each other total charge is divided into two equal parts. 
• Suppose a conductor A has charge Q and another conductor B has charged q and they are connected with each other, then each of them will have a charge equal to (Q + q)/2.
• Suppose a conductor A has charge Q and another uncharged conductor B are connected with each other, then each of them will have a charge equal to (Q/2).

CHARGING OF TWO SPHERES BY INDUCTION

Steps for charging of two spheres by induction.

1. We hold the two metal spheres on insulating stands and place them in contact.
2. We bring a positively charged glass rod near the left sphere. The left sphere then becomes negatively charged and the right sphere becomes positively charged.
3. We separate the spheres and they now have opposite charges. 
4. We remove the glass rod. The charges on the spheres get redistributed. Positive and negative charges now face each other. 
5. When the spheres are separated quite apart, the charges on them get uniformly distributed. 

CHARGING OF A SPHERE BY INDUCTION

Steps for charging of a sphere by induction

1. We take a metal sphere on an insulating stand and keep a negatively charged plastic rod near it. The near end of the sphere becomes positively charged and far end of the sphere becomes negatively charged.
2. Far end of the sphere is connected to the ground by a connecting wire to the ground. 
3. When the sphere is disconnected from the ground, the positive charge remain in the near end. 
4. When the plastic rod is removed, the positive charge is uniformly distributed on the sphere. 

BASIC PROPERTIES OF CHARGE:

• There are three basic properties of charge. They are 1. Additivity, 2. Quantization and 3. Conservation of Charge. 
• Additivity: Additivity of electric charge means that the total charge of a system is the algebraic sum of all the individual charges located at different points inside the system.
• Quantisation: The quantization of electric charge means that the total charge (q) of a body is always an integral multiple of a basic quantum of charge (e).

∴ q = ne, where n = ±1, ±2, ±3, ±4,.........

• Conservation: The laws of conservation of charge states that 
• The total charge of an isolated system remains constant. 
• The electric charges can neither be created nor destroyed, they can only be transferred from one body to another body. 

COULOMB'S LAW OF ELECTRIC FORCE:

Coulomb's law states that the force of attraction or repulsion between two stationary point charges is

1. Directly proportional to the product of the magnitude of the two charges.
2. Inversely proportional to the square of the distance between them and the force acts along the line joining the two charges. 

q₁ ⁕--------------- r ------------------⁕ q₂

If two point charges q₁ and q₂ are separated by a distance r, then the force F of attraction or repulsion between them is such that

 F ∝ q₁q₂  and  F ∝ 1 /r²

F = k q₁q₂/r²

[ Electrostatic force constant (k) ]

Where k is a constant of proportionality and it is called electrostatic force constant. 

The value of k depends on the nature of the medium between the two charges and the system of units used to represent the physical quantities. 

For the two charges located in free space and in SI units, 

 k = 1/(4πεₒ) = 9 x 10⁹ Nm²/C²

Where εₒ is called permittivity of free space. 

εₒ =  8.85 x 10⁻² C² N⁻¹m⁻²

Dimension of εₒ = [M⁻¹L⁻³T⁻⁴A²]

UNITS OF CHARGE

1. The SI unit of charge is Coulomb and denoted by C. 

2. CGS unit of Charge is two types

(i) in electrostatic CGS unit: statcoulomb or e.s.u. 

1 C = 3 x 10⁹ e.s.u. of charge. 

(ii) in electromagnetic CGS unit: abcoulomb or e.m.u. of charge.

1 C = 0.1 abcoulomb or e.m.u. of charge.

COULOMB'S LAW IN VECTOR FORM

RELATIVE PERMITTIVITY AND DIELECTRIC CONSTANT 

Permittivity

Permittivity is a property of a medium which determines the electric force between two charges situated in that medium. It is denoted by ε. Permittivity of vacuum or free space is minimum and it is denoted by εₒ. Permittivity of other medium are greater than εₒ. 

Relative Permittivity

The ratio (ε/εₒ) of the permittivity (ε) of a medium to the permittivity (εₒ) of free space is called relative permittivity (εᵣ ) of the given medium. 

Dielectric Constant (κ) 

Dielectric constant is defined as the ratio of the force between two charges placed some distance apart in free space to the force between the same two charges placed at same distance apart but in another medium. It is equal to relative permittivity. κ = εₒ. 

Dielctric constant for air = 1.00054

Dielctric constant for water = 80.

SUPERPOSITION OF ELECTROSTATIC FORCES

The principle of superposition states that when a number of charges are interacting, the total force on a given charge is the vector sum of the forces exerted on it due to all other charges. The force between two charges is not affected by the presence othe other charges.