COMBUSTION AND FLAME CLASS 8 SCIENCE NCERT IMPORTANT QUESTIONS

 COMBUSTION AND FLAME

 IMPORTANT QUESTIONS

combustion and flame

Fill in the blanks:

1. The substance which has a very low ignition temperature and can easily catch fire are called ----------.

2. The calorific value of a fuel is expressed as -----------.

3. ---------- is the only non-metal which catch fire if exposed to air.

4. The fire produced by oil and petrol cannot be extinguished by --------.

5. The burning of fuels like wood and cow dung cake releases unburnt ------- particles in the air.

MCQ

6. Light and heat are produced in the Sun by:

        a. burning wood

        b. oxygen

        c. nuclear reaction

        d. boiling water

7. The lowest temperature at which a substance catches fire is known as:

        a. burning temperature

        b. flaming temperature

        c. lowest temperature

        d. ignition temperature

8. Which among these are required for the production of a fire?

        a. fuel, water, heat

        b. fuel, oxygen, heat

        c. heat, burner, water

        d. heat, water, oxygen

9. During the explosion, there is an evolution of:

        a. light

        b. heat

        c. sound

        d. all of these

10. When we heat a paper cup containing water, it does not catch fire because:

        a. paper is inflammable

        b. water makes it wet

        c. ignition temperature of paper is not reached due to the presence of water

        d. none of these 

ASSERTION-REASON QUESTIONS

In the following questions, a statement of assertion(A) and a statement of the reason(R) are given. Select the correct option for the following assertion-reason questions:

a. Both A and R are true and R is the correct explanation of A.

b. Both A and R are true and R is not the correct explanation of A.

c. A is true but R is false.

d. A is false and R is true.

e. Both A and R are false.

11. Assertion(A)-Kerosene oil catches fire easily.

    Reason(R)-The ignition temperature of kerosene is very high.

12. Assertion(A)- Goldsmiths usually blow at the inner zone of a flame for melting gold.

    Reason(R)- The innermost zone of a flame is the hottest part.

13. Assertion(A)- Water is not suitable for fires involving oil and petrol.

    Reason(R)- Water sinks below the oil layer and oil keeps on burning on the top.

14. Assertion(A)- Charcoal does not form a flame.

    Reason(R)- Charcoal is a combustible substance.

15. Assertion(A)- CNG is a cleaner fuel.

    Reason(R)- CNG produces a very small amount of harmful products and is less polluting.

ANSWERS

1. Inflammable substances

2. kJ/kg

3. Phosphorus

4. Water

5. Carbon

6. nuclear reaction

7. ignition temperature

8. fuel, oxygen, heat

9. all of these

10. ignition temperature is not reached due to the presence of water

11. c

12. e

13. a

14. b

15. a

ATOMS AND MOLECULES CHAPTER 3 CLASS 9 NCERT NOTES AND STUDY MATERIALS -part 1

 ATOMS AND MOLECULES CHAPTER 3 CLASS 9

In our previous classes, we have studied matter and its different forms. The matter is something that has mass and they need space to occupy. In this chapter, you will learn about atoms and molecules.

many Indian and Greek philosophers have contributed much to the discovery of atoms by which matter is made up.

If we go on dividing any matter, we will reach a stage where no more further division is possible. Democritus called these particles atoms which means indivisible.

At the end of the 18th century, scientists were interested in studying how and when elements are combining with each other. That laid the foundation for establishing two important laws of chemistry called the laws of chemical combination by Lavoisier and Proust.

LAWS OF CHEMICAL COMBINATIONS

1. LAW OF CONSERVATION OF MASS

The Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.

Example- We can consider the reaction of Barium chloride with Sodium sulphate. Weigh them separately before the reaction. We can observe that the weight remains the same after the reaction. Here a chemical reaction has taken place and produced a white precipitate of barium sulphate and colourless sodium chloride. But the mass remains the same before and after the reaction.

2. LAW OF CONSTANT PROPORTIONS

The law was stated by Proust as " In a chemical substance, the elements are always present in definite proportions by mass."

Example- In water(H2O), the ratio of the mass of Hydrogen to the mass of Oxygen is always 1:8. Similarly in Ammonia(NH3), Nitrogen and Hydrogen are present in the ratio of 14:3.

Then comes the atomic theory by John Dalton. His theory gave an explanation to the law of conservation of mass and the law of constant proportion. According to Dalton, every matter is made up of small particles called atoms.

The postulates of Dalton's atomic theory are:

(i) All matter is made of very tiny particles called atoms.

(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.

(iii) Atoms of a given element are identical in mass and chemical properties. 

(iv) Atoms of different elements have different masses and chemical properties. 

(v) Atoms combine in the ratio of small whole numbers to form compounds.

 (vi) The relative number and kinds of atoms are constant in a given compound.

ATOM

The building blocks of all matters are atoms. All matter, whether an element, a compound or a mixture is composed of small particles called atoms.

It was Dalton who gave symbols for the atoms for the first time. Berzelius suggested that the symbols of elements be made from one or two letters of the name of the elements. Nowadays, IUPAC (International Union of Pure and Applied Chemistry) approves names of elements. Some symbols have been taken from the names of elements in Latin, German or Greek.

 

symbols of elements

Aluminium Al         Potassium K            Boron B                Hydrogen H

Copper Cu              Silicon Si                 Bromine Br           Iodine I

Nitrogen N             Sodium  Na             Carbon C               Lead Pb

Argon Ar                Silver-Ag                 Calcium Ca            Iron Fe

Fluorine F              Sulphur S                Chlorine Cl            Magnesium Mg 

Oxygen O              Uranium U               Cobalt Co              Neon Ne 

Barium Ba             Zinc Zn                    Gold Au 

    

Atomic Mass

Determining the mass of an individual atom was a relatively difficult task. So relative atomic masses were determined using the laws of chemical combinations and the compounds formed.

For a universally accepted atomic mass unit, carbon-12 isotope was chosen as the standard reference for measuring atomic masses.

 One atomic mass unit is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12. The relative atomic masses of all elements have been found with respect to an atom of carbon-12.

The atomic mass of certain elements are listed below:

Hydrogen- 1      Carbon- 12         Nitrogen -14 

Oxygen -16        Sodium- 23         Magnesium- 24 

Sulphur -32         Chlorine -35.5     Calcium -40

Molecule

A molecule can be defined as the smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance. 

Atoms of the same element or of different elements can join together to form molecules.

A molecule of certain elements contain only one atom, but some elements may contain more than one atom. The number of atoms present in a molecule says about its atomicity.

The atomicity of Fe, Na, Ar and He is one. Hence they are monoatomic molecules.

The atomicity of O2, H2, N2, Cl2 and F2 is two. Hence they are called diatomic molecules.

Ozone O3 is a triatomic molecule, Phosphorus P4 is tetra atomic and Sulphur S8 is polyatomic with atomicity 8.

Atoms of different elements join to form compounds. We can find their atomicity by counting the number of atoms present in them. 

Eg. The Atomicity of Water H2O is 3, CO2 is 3, Ammonia NH3 is 4.

Ions

Atoms carrying charges are called ions. The charged species can be positive or negative. A positively charged ion is called a cation and a negatively charged ion is called an anion.

Sodium chloride contains Na+ cation and Cl- anion. Magnesium chloride contains Mg²⁺ and Cl-.

Ions can be present as a single charged atom or a group of atoms. Polyatomic ions are a group of atoms carrying charge. Example: OH-(hydroxide),  SO4²⁻(sulphate)

Writing Chemical Formula

What is chemical formula? As a beginner, you may always wonder how to write a chemical formula. A compound's chemical formula is a symbolic representation of its composition. A learner can easily understand the elements present in a compound by looking at the chemical formula. Moreover, it gives the number of atoms of each element present in it.

In order to write a chemical formula, we must learn the symbols and valency or combining capacity of elements.

Valency- the combining capacity of an element is called its valency. 

In water H2O, one atom of Oxygen is combined with two atoms of Hydrogen. So the valency of O is 2. 
In NaCl, the valency of sodium and chlorine is 1 as it combines with one atom only.

In Aluminium chloride, AlCl3, the Valency of Al is 3 and the valency of Cl is 1. It is very evident that Al is combined with 3 atoms of Cl and Cl is combined with one atom of Al.

Valencies of some common ions and polyatomic ions are given in Table3.6 of the NCERT Science textbook. 

The rules for writing a chemical formula are:

• The valencies or charges of the ions must balance in a compound and overall structure must be neutral.
• the symbol of metals should be written first followed by the symbol of non-metal (eg: FeS)
• If there is more than one polyatomic ion, they should be enclosed in a bracket. (eg: Al2(SO4)3)

Steps for writing the chemical formula

Write the symbol of atoms present in a compound.

Write the valency or charge of each one under the symbol.

Crossover the valencies of the combining atoms and write it as a subscript on the right side of the symbol (like MgCl2)

If the valency is 1 on each atom, no need to specify it in the symbol (like NaCl).

Use brackets for more than one number of the same polyatomic ions (like Ca(OH)2 )

Sodium carbonate

Na        CO3

1            2

Crisscross the charges or the valencies.

We can write the chemical formula as Na2CO3

(Valency of sodium Na is 1 and hence it is not to be mentioned) 

COAL AND PETROLEUM CLASS 8 EXTRA QUESTIONS INCLUDING ASSERTION REASON TYPE QUESTIONS

             COAL AND PETROLEUM

coal and petroleum

EXTRA QUESTIONS INCLUDING ASSERTION REASON 

FILL IN THE BLANKS

1. Earlier --------- was used in railway engines to produce steam to run the engine.

2. The slow process of conversion of dead vegetation into coal is called -----------.

3. Coal, --------- and natural gas are fossil fuels.

4. The resources that are present in unlimited quantity in nature and are not likely to be exhausted are called ----------.

5. A petroleum product, -------- is used in place of coal tar for surfacing the road.

6. ----------- is obtained during the processing of coal to get coke.

7. Naphthalene balls which is used as a moth repellent is obtained from ---------.

8. The word petroleum is derived from the words -------- and -------.

9. Coal is of plant origin and --------- is of animal origin.

10. Refining of petroleum is carried out in ------------.

11. ------- is a less polluting fuel and is said to be a cleaner fuel.

12. Petroleum is called ----------- due to its great commercial importance.

MCQ

1. Which among these is an inexhaustible natural resources?

a. coal    b. petroleum    c. sunlight    d. natural gas

2. Which product of coal is used in the manufacture of steel?

a. coal tar    b. coke    c. coal gas    d. bitumen

3. The process of separating the various fractions of petroleum is called --------

a. mining    b. filtering    c. carbonisation    d. refining

4. Which among these petroleum product is used as a solvent for dry washing?

a. petrol    b. diesel    c. kerosene    d. paraffin wax

5. ------- is used in thermal power plant to produce electricity.

a. petrol    b. coal tar    c. coal    d. coke

ASSERTION-REASON QUESTIONS

In the following questions, a statement of assertion(A) and a statement of reason(R) is given. Select the correct option for the following assertion-reason questions:

a. Both A and R are true and R is the correct explanation of A.

b. Both A and R are true and R is not the correct explanation of A.

c. A is true but R is false.

d. A is false and R is true.

1. Assertion- The amount of exhaustible natural resources are limited.

   Reason- Exhaustible  natural resources are not likely to be exhausted by human activities.

2. Assertion- Coal is a fossil fuel.

   Reason- Coal is formed from the remains of vegetation.

3. Assertion- CNG is cleaner fuel.

   Reason- CNG can be supplied directly through pipes.

4. Assertion- Coal, petroleum and natural gas can be prepared in the laboratory.

   Reason- Formation of fossil fuel is a very slow process.

5. Assertion- The layer of petroleum and natural gas are seen above the water layer in oil wells.

   Reason- Petroleum and natural gas are lighter than water.

ANSWER THE FOLLOWING: 

1. Name any two places in which natural gas is found in India.

2. Name the different products obtained on processing of coal.

3. Name three fossil fuels.

4. Name the fraction of petroleum which is used in road surfacing.

5. List out any six constituents of petroleum.

6. Expand CNG.

7. Differentiate between exhaustible and inexhaustible natural resources.

8. What are fossil fuels?

9. What is carbonisation?

10. Write any three uses of coal.

11. What is refining of petroleum?

12. What are the characteristics of coke?

13. Explain the of formation of coal. 

14. Explain the formation of petroleum.

15. List out any four ways by which we can save fossil fuels. 

ANSWERS

FILL IN THE BLANKS:

1. coal

2. carbonisation

3. petroleum

4. inexhaustible natural resources

5. bitumen

6. coal gas

7. coal tar

8. petra, oleum

9. petroleum

10. petroleum refinery/ refinery

11. CNG

12. black gold

MCQ

1. sunlight

2. coke

3. refining

4. petrol

5. coal

ASSERTION-REASON TYPE

1. c

2. a

3. b

4. d

5. a

SOIL CHAPTER 9 CLASS 7 SCIENCE NOTE- STUDY MATERIAL

SOIL CHAPTER 9 CLASS 7 SCIENCE NOTES

                                SOIL 

There are many natural resources on earth. Soil plays an important role among them. Soil provides shelter for many animals. We can see many organisms in the soil which dwell their life in it. It helps human beings also in many ways. Our crops, forests, water resources, buildings, and constructions are very much related to the soil.

You can collect soil samples from different places and observe the kind of insects and small organisms present in them. Different plants and herbs can be seen in it. Tabulate your result and make a comparative study of it.

 

Collect a sample of soil from your garden. Put that soil in a transparent glass tumbler of water. Stir it properly and allow it to settle down. Observe the distinct layers seen in the tumbler.

We can see that the heavy gravel particles are settling at the bottom of the tumbler. Just above that layer, we can observe sand particles. Clay particles are finer and smaller than sand and hence it will be settling on top of the sand. There will be a muddy water layer just above the clay layer. Water will become more clear as time passes and it will be visible as a separate layer. Very lighter and less dense things will be floating on the top layers. It may include dry leaves, animal remains, and twigs.

HUMUS

The rotting dead matter of plants and animals present in the soil is called humus. Normally the top layer of the soil will be rich in humus.

SOIL PROFILE

How soil is formed on earth? Have you ever thought of the formation of soil on earth?

The soil we see today has been formed through different processes that occurred in nature. The rocks that were there on earth undergone many changes due to climate change, rain, heat, and flowing water. 

Water that gets collected in the cracks of rocks will be freezing at night and it expands to make bigger cracks on it. It started breaking down into smaller pieces and might have carried by the wind or water. 

The process of breaking down rocks into the soil by the action of wind, water, and climate is called weathering.

When you are taking a ride in a hilly place, you can see the vertical cross-section of soil through which the roads are made. Have you noticed the difference in the colour and texture of each layer?

SOIL PROFILE

The vertical section through various layers of soil is called a soil profile.

These layers in a soil profile are called horizon. Each horizon will be of different colour, texture, depth, and composition.

We can discuss the features of these horizons in detail.

A-HORIZON or TOPSOIL

• It is the uppermost layer of the soil.
• It is dark in colour as it is rich in humus and minerals.
• It is soft and porous.
• It can retain more water.
• It is a shelter for many animals.
• It helps the roots of plant to spread easily through the soil.

B-HORIZON

• It is the next layer to the topsoil.
• It has a lesser amount of humus.
• It has more amount of minerals.
• It is generally harder and more compact than the topsoil.

C-HORIZON

• It is the third layer of the soil profile.
• It is made up of small lumps of rocks with cracks and crevices.

BEDROCK

• It is the last layer of the soil profile.
• It is the hardest layer.
• It contains a bed of rock which is difficult to dig with a spade.

TYPES OF SOIL

Soil formed from rocks in different places will be different in its composition.

Soil may contain different proportions of rock particles, clay, and humus.

The soil is classified into three types based on the proportion of particles present in it.

a. Sandy soil

b. Loamy soil

c. Clayey soil

The soil which contains a greater proportion of big particles is called sandy soil.

SANDY SOIL

If the proportion of fine particles present in the soil is higher, it is called clayey soil.

CLAYEY SOIL

If the proportion of large particles and fine particles are almost the same, it is called loamy soil.

LOAMY SOIL

DIFFERENCE BETWEEN SANDY, LOAMY AND CLAYEY SOIL

SANDY SOIL

• The particle size of the soil is large.
• There is a large space between the particles and it cannot fit closely together.
• Sand is well aerated.
• Water can drain quickly through the space between the particles.
• Less water holding capacity.
• Sand is light and dry.

CLAYEY SOIL

• The particle size is very small.
• The soil particles are tightly packed and there is very little space between them.
• Sand is less aerated.
• Water will not drain easily.
• Water holding capacity is more.
• It is heavier as it holds more water.
• It is the best soil for making pots, statues, and toys.

LOAMY SOIL

• Loamy soil is the best soil for the growth of the plants.
• It is a mixture of sand, clay, and silt.
• It has the right amount of humus.
• it has the right water holding capacity.

* SILT- It is the deposit of soil seen at the river bed. The particle size of silt is between sand and clay. It is very fertile as it carries all the minerals from the hills and mountains. it helps in the growth of plants.

PROPERTIES OF SOIL

The important properties that we are going to discuss are the percolation rate of the soil, moisture in the soil, and the water absorption capacity.

PERCOLATION RATE

Have you ever noticed how fast water seeps down through the soil? If you are collecting different samples of soil, the amount of water that seeps down will be different. Why it is so?

The time taken by the water to percolate through a particular sample of soil depends upon the particle size of the soil. We can observe that the time for percolation will be less in the case of sandy soil as it is loosely packed. Water goes down very fast through it.

So percolation rate can be calculated for a particular sample of soil by knowing the amount of water percolated and the time taken for percolation.

Percolation rate (ml/min) = amount of water(ml) /percolation time(min)

If a given sample of soil has taken 10 minutes to percolate 300 ml of water, the percolation rate will be 300/10=30ml/min.

MOISTURE IN SOIL

If you are heating a sample of soil from your garden in a test tube, you can observe tiny droplets of water getting condensed on the inner sides of the test tube. Where does this water come from?

It is due to the moisture or the water content present in the soil.

On a hot summer day, we can observe the air above the hot soil shimmering. The water vapour which is coming out of the soil reflects the sunlight and it appears to shimmer. Hence we can conclude that there is moisture present in the soil.

ABSORPTION OF WATER BY SOIL

Different types of soil will be absorbing water to a different extent.

The amount of water retained by clayey soil will be more than that of sandy soil.

An activity can be performed to observe this. 

Take a funnel and pour a known amount of soil into it. Note down the initial volume of water in a measuring jar and start pouring that into the soil. Make sure that you are pouring it all over the soil. 

Look at the tip of the funnel. When it starts dripping, stop pouring and note down the final volume of water. The difference will give you the volume of water absorbed by the soil.

The percentage of water absorbed by the soil can be found using the equation;

Percentage of water absorbed = U-V/W x100

where U is the initial volume of water in the measuring cylinder, V is the final volume of water in the measuring cylinder and W is the weight of the soil.

SOIL AND CROPS

Wheat and gram - clayey soil and loamy soil which is good at retaining water.

WHEAT

Paddy- clayey soil is rich in clay and organic matter and can retain more water.

PADDY

Lentils and pulses- loamy soil that drains water easily.

Cotton - sandy loam or loamy soil that can drain water easily and are well aerated.

COTTON FARM

In this chapter, you have learned about the formation of soil, soil profile, types of soil, and the properties of soil. You have already studied soil erosion and soil pollution in your geography lessons. The activities that are mentioned in the NCERT textbook can be performed at home to make the concepts more clear. This abstract of soil chapter 9 class 7 notes will definitely help you to enhance your knowledge of this chapter.

METALS AND NON-METALS NOTES PART-2 CLASS 10 NCERT

NCERT 2020-2021 CLASS 10- METALS AND NON-METALS NOTES PART-2

CHEMICAL PROPERTIES OF METALS
 

NCERT CLASS 10- 2020-2021-METALS AND NON-METALS- NOTES- PART-2- CHEMICAL PROPERTIES OF METALS

You have studied the physical properties of metals and non-metals. The metals can be distinguished more from non-metals by studying the chemical properties of metals. From class 10 metals and non-metals, you can expect many application-level questions.

You have studied earlier that on burning the magnesium ribbon, white ash is produced. Magnesium burns with a dazzling flame and when this white ash is dissolved in water and tested with red litmus paper, it turns blue in colour.

Another activity for a non-metal can be performed. Sulphur is taken in a china dish and it is heated over a Bunsen burner. 
Some gas is evolved and when this gas is collected by bringing an inverted test tube and then it is dissolved in water. It is found that it turns blue litmus to red in colour.

So now we will discuss the chemical properties of metals. 
What happens when metals are burnt in the air? 
Different metals are taken and burned in the air and it is found that different metals react with air differently. 

 
Some metals like sodium and potassium burn in the air without heating. When they are exposed to air they will burn and convert into oxide. There are some other metals that react on heating strongly in air and form their oxides on reacting with oxygen present in the air.

 So a general equation can be written.
 Metal + Oxygen →  Metal oxides

We have studied in the previous chapter that copper is a reddish-brown powder. When it is heated in the air, it forms black coloured cupric oxide.  So the balanced chemical equation can be written:
 2 Cu + O2  → 2 CuO
Similarly aluminium on heating in the air forms aluminium oxide. Its formula is Al2O3.
Balanced a chemical equation is:
 4Al  +  3 O2 → 2 Al2O3
Metal oxides react with the acids and form salt and water. So metal oxides are basic oxides or behave as bases and form salt and water.
Amphoteric oxides- There are certain oxides which on dissolving in water behave as acids and bases. They show both acidic and basic nature. Some metals react with acids as well as bases and form salt and water. Such oxides are called amphoteric oxides.

 
These oxides not only react with the acids they also react with the bases and form salt and water. Aluminium oxide and Zinc oxide are examples.
Al2O3 reacts with hydrochloric acid and forms aluminium chloride and water.
Al2O3 + 6 HCl →2AlCl3 + 3 H2O
Aluminium oxide also reacts with a base, ie, sodium hydroxide and it forms sodium aluminate.
Al2O3  + 2 NaOH  → 2 NaAlO2  +  H2O

The reaction of metal oxides with water

The reaction of metal oxides with water also comes under the chemical properties of metals. Most metal oxides are insoluble in water. 
 Some of the metal, oxides dissolve in water and form alkalis. 

Sodium oxide and potassium oxide react very violently with water and form sodium hydroxide and potassium hydroxide.  So these water-soluble hydroxides are also called alkalis. 
Na2O + H2O → 2 NaOH 
K2O + H2O → 2 KOH
Sodium, as well as potassium, react vigorously. So when these metals are exposed to the air they will catch fire. That is why both sodium and potassium metals are kept immersed in kerosene oil so that they do not come in contact with the oxygen present in the air. 

To avoid accidents precaution has to be taken. These metals should not be touched with wet hands.
Metals like magnesium, aluminium, zinc and lead also continuously keep reacting with the oxygen present in the air and they get covered with a layer of their oxides. This oxide layer protects these metals from further oxidation. 

The metal underneath does not further undergo oxidation. The oxide layer acts as a protective layer.
Iron does not burn when heated but if the iron filings are sprinkled over the flame, it will burn.  Copper does not burn. Silver and gold are the very least reactive metals. They do not react with oxygen even at high temperatures and do not form oxides.

When silver jewellery or silver articles are exposed to air for a long time, it becomes black in colour. It forms silver sulphide on reacting with hydrogen sulphide gas (H2S) present in the air.

silver sulphide coating

Anodizing- certain metals react with the oxygen present in the air and form an oxide layer which acts as a protective layer and this property is used for making certain cooking utensils and some decorative pieces by the process of anodizing. 

Aluminium metal is covered by an aluminium oxide layer which prevents it from further oxidation which prevents it from corrosion.

How anodizing is done? By electrolysis. The aluminium utensil or any aluminium object to be coated with an aluminium oxide layer is made anode and any other metal is made the cathode. It is electrolyzed using dilute sulphuric acid. 

Oxygen gas will be liberated at the anode which will react with aluminium and cover it with the layer of aluminium oxide which acts as a protective layer. This aluminium oxide layer can also be further dyed into different colours to make it more attractive.

 Thicker is the layer of aluminium oxide, protection will be more.

Anodized and dyed article

What happens when metals react with water?

Some metals react with cold water and some metals react with hot water and it has been found that some metals react with steam.

Metals react with water to form a metal oxide and hydrogen gas is liberated. Now, these metal oxides further react with water and form metal hydroxides.

Metals + Water→   Metal oxide + Hydrogen

Metal oxide + Water →   Metal hydroxide 

So let us see which are the metals that react with cold water and how do they react.

• Some of the metals react violently with water producing a lot amount of heat like sodium and potassium.  It is a very violent reaction and this reaction must be performed very carefully because the reaction is so much exothermic. The hydrogen gas liberated catches fire immediately.

• Calcium also reacts with cold water, but the reaction is not so violent.  It forms calcium hydroxide and hydrogen gas is liberated.

•  Magnesium does not react with cold water. It reacts with hot water and forms magnesium hydroxide and hydrogen gas. 
• Some metals do not react with hot water. Metals like aluminium, iron and zinc react with steam.

 ACTIVITY

An activity can be performed in which these metals will react with steam in a glass tube. The sample of the metal is taken and glass wool soaked in water is taken at one end of a dry glass tube and it is heated with the help of a Bunsen burner. Metal is a good conductor of heat. 

Steam will be formed which will react with the metal and the gas liberated is collected over water and this gas is hydrogen gas. When it is tested by bringing a burning match stick, it burns with a pop sound.  So the metals which react with the steam are aluminium, iron and zinc.

• Aluminium reacts with steam and it forms aluminium oxide and hydrogen gas. Same way iron reacts with steam and forms ferric oxide and hydrogen gas. In the same manner, zinc also forms zinc oxide and hydrogen gas is liberated.
• Metals like lead, copper. silver and gold do not react with water at all.

 How do metals react with acids?

An activity can be performed by taking various metals and testing them with dilute acids in the lab and seeing how these metals react with acids. Metals like sodium and potassium react violently with dilute acids. The reaction must be performed very carefully because it is an exothermic reaction.

Metal  + dilute acid   →  salt + hydrogen gas

As I have told you earlier sodium reacts violently with dilute hydrochloric acid and it forms salt sodium chloride and hydrogen gas.

2Na + 2HCl →  2NaCl  + H2

Magnesium reacts with HCl and forms the salt magnesium chloride and hydrogen gas.

Mg  + 2HCl →  MgCl2  + H2

Aluminium and Zinc also reacts with HCl. Now you can write the equations yourself.

So in this case what will be formed? Think over it and write it.

In the case of iron, ferrous chloride and hydrogen will be formed.

Now let us see what happens in the case of Copper. Copper is very less reactive and does not react with dilute HCl. No reaction occurs.

Write equations of the various metals with sulphuric acid yourself in the same manner. Various salts will be formed and hydrogen gas will be liberated.

Most of the metals do not react with nitric acid because nitric acid is a very strong oxidizing agent. It oxidizes the hydrogen gas liberated to water and nitric acid itself gets reduced to the oxides of nitrogen like dinitrogen oxide N2O nitric oxide NO and nitrogen dioxide NO2.  

So hydrogen gas is not liberated in the case of nitric acid reacting with metals.

But the metals like manganese and magnesium react with very dilute nitric acid and form salt and hydrogen. So manganese on reacting with nitric acid forms manganese nitrate and hydrogen gas and in the case of magnesium, the salt formed is magnesium nitrate.

Copper does not react with any of the dilute acids as we have discussed earlier. Other metals like silver, gold and lead also do not react with the dilute acids.  

Aqua Regia is a homogeneous mixture of concentrated nitric acid and concentrated HCl. One part concentrated nitric acid and three parts concentrated hydrochloric acid. The ratio of 1:3. 

It can dissolve the metals like platinum and gold. These metals do not dissolve in any of the acids but dissolve in the aqua regia.

How do metals react with the solutions of other metal salts?

 For studying this property an activity can be performed by taking two test tubes. In one test-tube iron nail is taken and it is dipped in copper sulphate solution which is blue in colour.

In another test tube, a copper nail is taken and it is dipped in FeSO4 solution which is green in colour. Now keep it aside for some hours and then observe the changes.

blue coloured CuSO4 & green coloured FeSO4

You will find that in the first test tube, the iron nail surface is covered by a reddish-brown layer and the colour of the copper sulphate solution is also a  bit faded whereas there is no change in the other test tube. 

Do you know why? You have already studied it. Think over it. Why has this happened?

Let us discuss a general reaction.

Metal A + Salt solution of Metal B →  Salt solution of Metal A + Metal B

Metal A has displaced metal B from its salt solution. ie, metal A is more reactive than metal B. We can now write the equation as follows:

 Fe + CuSO4  →  FeSO4 + Cu

The solution of ferrous sulphate is green in colour. So the light green colour will be obtained and you will find that the outer surface of the iron nail has become reddish-brown in colour due to the deposition of copper metal.

It clearly shows that iron is more reactive than copper. A displacement reaction has occurred.

You have studied earlier that a more reactive metal displaces a less reactive metal from its salt solution.

Now in the second test tube, copper is less reactive than iron and hence no reaction will occur.

Cu + FeSO4 → No reaction

Another activity is performed with a copper nail or a thin sheet of copper. It is placed in a silver nitrate solution. Will the reaction occur? Think over it?

In this particular case, the reaction will occur and copper nitrate will be formed and greyish white silver will be deposited on the surface of copper. What does it show? It shows that copper is less reactive than silver. 

On the basis of the displacement reaction, we come to know about the metals. We know about the reactivity of the various metals based on which a reactivity series can be made.

What is a reactivity series? It is the arrangement of metals in the decreasing order of their reactivity. It has a major role in the study of the chemical properties of metals.

Reactivity series

Potassium     (most reactive)

Sodium

Calcium

Magnesium

Aluminium 

Zinc

Iron 

Lead

Hydrogen

Copper

Mercury

Silver

Gold  (least reactive)

Potassium is the most reactive metal and gold is the least reactive metal. At the top are the most reactive metals and are good reducing agents and at the bottom are the least reactive metal. 

Do metals and non-metals react to each other?

We have studied earlier the reaction of metals with various reagents and now we will study how metals and non-metals react with each other. Why do metals and non-metals react?

To understand this let us study noble gases, metals and non-metals. Their electronic configuration will tell us the reason behind the reaction of metals and non-metals.

As you know noble gases are unreactive and have a stable electronic configuration. Their outermost shell is complete. All the noble gases have either two electrons in the outermost shell-like helium or eight electrons in the outermost shell-like neon or argon.

So let us first of all study why noble gases are inert in nature. Noble gases do not react because they already have a stable electronic configuration. Helium has 2 electrons in the outermost shell and this is a stable configuration.

Neon - atomic number 10 -  10 electrons- two shells -2,8 .

It has eight electrons in the outermost shell. This is a stable electronic configuration. It is inert in nature.

Argon has 18 electrons -2,8,8 .It is also inert in nature and chemically inactive.

Now let us study the electronic configuration of metals and non-metals.

Sodium - atomic number -11 -  11 protons and 11 electrons. The electronic configuration is 2,8,1. The outermost shell or valence shell is not complete. It has one electron in the outermost shell.

Magnesium -12 electrons. -2,8,2. It has two valence electrons.

Aluminium  - 13 electrons -  2,8,3. Three valence electrons are there.

Potassium -19 electrons - 2,8,8,1. one valence electron

Calcium -20 electrons - 2,8,8,2. It has 2 valence electrons

 So all these metals do not have a stable electronic configuration. What do we conclude from this? Metals react to attain inert gas configuration by losing electrons. If they lose the electrons from the outer shell to react they will attain an inert gas configuration or stable configuration.

Let us take the case of non-metals

Nitrogen -7 electrons  - 2,5

Oxygen -8 electrons -  2,6

Fluorine – 9 electrons -  2,7

Phosphorous - 15 electrons - 2,8,5

Sulphur -16 electrons- 2,8,6

Chlorine – 17 electrons -  2,8,7

Nitrogen has five electrons in the outermost shell and to attain inert gas configuration, it needs three more electrons. Oxygen has six electrons in the outermost shell and they need 2 more electrons for stable configuration.

Octet means having eight electrons in the outermost shell and if there are two electrons in the outermost shell, it is called duplet.

The same is the case with fluorine also. Has one electron less to attain octet.

So we can arrive at the conclusion that metals and non-metals react to complete their duplet or to complete their octet to attain inert gas configuration or a stable configuration.

Now let us take the case of metal sodium.

Sodium as you have seen it has one valence electron. We can represent sodium atoms by electron dot structure which is called the electron-dot representation of an atom.  Electron dot structure is written by writing the number of valence electrons on the symbol in the form of dots. So one dot is made on the symbol of sodium.

Na x

If sodium loses one electron it will attain an inert gas configuration.  So here it is 2,8,1.  After losing one electron, it attains the configuration of noble gas and becomes Na+.

Na → Na⁺  +  e⁻

But by losing one electron it also gains a unit positive charge because the number of electrons is less now and the number of protons is the same. That is eleven electrons became ten now.

 Electronic configuration of Cl is 2,8,7. So it has seven valence electrons. 

  xx                   

x Cl xx

  xx

The electron lost by the sodium atom is gained by chlorine and it becomes Cl⁻. Minus sign shows that the electron is negatively charged.

                       xx                   

  Na x ↗     x Cl xx

                       xx 

 

Cl  + e⁻  →  Cl⁻

Chloride ion has attained the configuration of argon(2,8,8). Sodium-ion has attained the configuration of neon(2,8). When these oppositely charged ions come close to each other they are attracted strongly by the electrostatic force of attraction and they form sodium chloride. 

Na⁺  + Cl⁻  →  NaCl

We can also discuss the case of MgCl2 (magnesium chloride). Magnesium has two valence electrons.

By losing these two electrons it also attains inert gas configuration and becomes stable and gains two-plus charges, whereas two chlorine atoms gain two electrons and form two chloride ions. Mg²⁺ and two Cl⁻ attract each other and form MgCl2. These types of compounds are called ionic compounds or electrovalent compounds.

Ionic compounds are formed by the transfer of electrons from one atom to another.

You can find some more ionic compounds and write down the electron dot structure and see how they are formed. Metals will lose electrons and form positive ions and non-metal will gain the electrons to form the negatively charged ions.

Properties of ionic compounds

• Ionic compounds are generally crystalline solids. Generally, ionic compounds are hard and crystalline solids because oppositely charged ions are packed together with strong electrostatic forces of attraction. That is why ionic compounds are solid and they are brittle. They easily break on being hammered.

crystal salt

• To study the next property an activity can be performed. Take an ionic compound in a spatula. Heat it over the flame of Bunsen Burner.

It is found that only on prolonged heating does sodium chloride melt. It has a very high melting point.

All the ionic compounds have very high melting and boiling points. The positively charged ions and negatively charged ions are held together by strong electrostatic forces of attraction and a lot of energy is required to separate them.

• Another property is solubility. Different ionic compounds like NaCl, KCl or MgCl2 are taken and their solubility in water and organic solvents like alcohol or ether is checked. It is found that ionic compounds are soluble in water, but are insoluble in organic solvents like alcohol and ether. Ionic compounds are insoluble in kerosene and petrol also.

• It shows that when NaCl is dissolved in water, sodium ions and chloride ions separate and allow the current to pass through the solution. Sodium chloride in the solid state does not conduct the electric current. In the molten state also sodium ions and chloride ions present in it will allow the current to pass through them.

Moreover, the electrostatic force of attraction between the ions is overcome due to the heat. So ionic compounds are good conductors of electricity in the solution form when dissolved in water or in the molten state. 

FOR PART -1 METALS AND NON-METALS-PLEASE CHECK




The chemical properties of metals is a very important topic from class 10 metals and non-metals in the examination point of view. Chemical equations from this topic are very important. You have to draw and practice the electron dot structure of the formation of different ionic compounds.