HOW TO STUDY ACTIVITIES OF CHAPTER 1 CHEMICAL EQUATIONS AND REACTIONS? CLASS 10 NCERT

CHEMICAL REACTIONS AND EQUATIONS- CHAPTER-1 -NCERT CLASS 10- CHEMISTRY- ACTIVITIES 

chemical reactions and equations activities class 10 

In this chapter, you are going to study chemical reactions.

The various sub-topics included are characteristics of chemical reactions, balancing chemical equations, the implication of balanced chemical equation, four types of chemical reactions like the combination, decomposition, displacement, double displacement, precipitation reactions, neutralisation, oxidation and reduction.

Many activities involving chemical reactions are given in your NCERT textbook and these are very important in the examination point of view. In previous years board exams, you can find many questions from these activities including diagrams.

So we shall start with some activities. More emphasis is given for the colour change during the activities. This will help you to crack questions from these sections.

ACTIVITY-1.1  explains the reaction of Magnesium with Oxygen. On burning magnesium ribbon in air, it makes a dazzling light with oxygen to form a white powder. It is magnesium oxide.

Mg + O2 → MgO

ACTIVITY- 1.2 explains the reaction of lead nitrate and potassium iodide. It will undergo a double displacement reaction to form lead iodide which is a yellow precipitate and potassium nitrate which is colourless. (*an example for double displacement and precipitation reaction).

Pb(NO3)2 + 2KI → PbI2 + 2KNO3

ACTIVITY- 1.3 explains the reaction of zinc granules with dilute HCl or dilute H2SO4.The resultant products are hydrogen gas and zinc salts like ZnCl2 or ZnSO4. 

We can observe the bubbles of hydrogen gas around the zinc granules and can test the presence of hydrogen with the pop sound of a burning match stick. This reaction is exothermic and that is why the test tube is becoming hot during this reaction(* example for displacement reaction or exothermic reaction).

Zn + 2HCl → ZnCl2 + H2

CHANGES ACCOMPANYING A CHEMICAL REACTION are:

• change in state
• change in colour
• change in temperature
• evolution of gas

CHEMICAL EQUATIONS

Reactants → Products

Word equation- Shows change of reactants to products with an arrow between them.

Magnesium + Oxygen → Magnesium oxide

Unbalanced equation / skeletal equation- the number of atoms or the mass is not the same on the reactant side and product side.

Mg + O2 → MgO

Balanced equation - the reaction in which the number of atoms is the same on the reactant side and product side. The total mass of the reactants will be equal to the total mass of the products. 

Mg + O2 → 2 MgO

* Balancing of a chemical reaction is based on the law of conservation of mass. It states that mass can neither be created nor destroyed in a chemical reaction.

ACTIVITY 1.4- explains the reaction of calcium oxide (quick lime) with water. This is an example of the combination reaction where CaO reacts with water to form calcium hydroxide Ca(OH)2. During this reaction, a large amount of heat is produced(exothermic reaction).

CaO + H2O → Ca(OH)2

ACTIVITY- 1.5 explains about the decomposition reaction of ferrous sulphate crystals. On heating light green coloured ferrous sulphate in a dry test tube, FeSO4.7H2O loses its water of hydration and will become white coloured anhydrous ferrous sulphate (FeSO4). 

On further heating, it decomposes to form a dark brown coloured solid. the products formed are ferric oxide, sulphur dioxide and sulphur trioxide.

FeSO4.7H2O → FeSO4

2FeSO4 → Fe2O3(s) + SO2(g) + SO3(g)

ACTIVITY-1.6 explains about the thermal decomposition of lead nitrate. Lead nitrate is a white coloured powder. On heating, it will decompose to form a lead oxide, nitrogen dioxide and oxygen. The observation is the formation of brown fumes of nitrogen dioxide.

2Pb(NO3)2 → 2PbO + 4NO2 + O2

ACTIVITY - 1.7  explains about the electrolytic decomposition of water into hydrogen and oxygen. 

On electrolysis, the bubbles are formed and it can be tested using a burning candle. Hydrogen burns with a pop sound. We can notice that the volume of the gas formed is not the same. 

When two volumes of hydrogen are formed, only one volume of oxygen is formed. It is clear from the balanced equation given below:

 2 H2O → 2 H2 + O2

ACTIVITY -1.8 explains about the photolytic decomposition of silver chloride (AgCl). When white coloured silver chloride is exposed to sunlight, it will decompose to form grey coloured silver and chlorine gas.

2AgCl(s) → 2Ag(s) + Cl2(g)

 Similar is the case with silver bromide.

2AgBr(s)  → 2 Ag(s) + Br2(g)

ACTIVITY- 1.9 explains the displacement reaction of the iron nail with copper sulphate. This topic was already studied in lower grades. The more reactive metal can displace a less reactive metal from its salt. So in this activity iron being more reactive displaces copper from copper sulphate.

iron nail

blue coloured copper sulphate and green coloured iron sulphate

 

The blue colour of copper sulphate fades and changes into a light green colour due to the formation of iron sulphate. Brown deposits of copper can be observed on iron nails.

Fe + CuSO4 → FeSO4 + Cu

 ACTIVITY -1.10 explains about the double displacement reaction of barium chloride and sodium sulphate. On adding these, it undergoes double decomposition to form a white precipitate of barium sulphate and sodium chloride. This is an example of precipitation reaction as well.

Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

a white precipitate of barium sulphate

* Another example for precipitation reaction was a reaction with lead nitrate and potassium iodide(yellow precipitate of lead iodide).

ACTIVITY-1.11 explains about the oxidation reaction of copper powder. Brown coloured copper powder on heating reacts with oxygen in the air to form black coloured copper oxide.

2Cu + O2 → 2 CuO

brown coloured copper vessels

copper oxide coating on a copper vessel

Do you want to study acids, bases and salts and metals and nonmetals? You can refer my blog for these topics.

YOU CAN ALSO READ: ACIDS, BASES AND SALTS

NCERT SCIENCE CLASS 6--sorting materials into groups -chapter 4- study material

SORTING MATERIALS INTO GROUPS- CHAPTER 4 -IMPORTANT TOPICS

NCERT SCIENCE CLASS 6--sorting materials into groups -chapter 4- study material

Look at this picture. How nicely the hats are arranged on each shelf! Have you ever wondered why we are sorting and arranging things? What is the need for sorting different materials and which are the criteria for sorting? Is sorting materials into groups makes our task easier?

In this session, we can discuss the sorting of materials into groups based on their properties. The objects we see around us are made up of one or more materials like metal, plastics, glass, wood, mud, etc. You can make a list of materials that are around you and group them according to the material by which it is made up of.

Certain objects that we choose may be using different materials. For example, you may have chairs made up of wood, plastic, or metals at home.

plastic chair

wooden chair

Similarly, we can find that a plate, pen, or cot made of different materials. Make a list of objects and the materials by which each one can be made.

Contrary to this, we can think about a material like wood or plastic and list out objects made by this. For example, using cotton, we can make clothes, bed sheets, bags, curtains, etc. Make a table of items like this and find out five items each.

So we can find that objects around us are made of different materials and one material could be used for making many different objects.

PROPERTIES OF MATERIALS

When we are choosing a material for making an object, we need to consider many things like its availability, properties, cost factor, manufacturing methods, etc. Among this, the most important factor is the properties of the material. If we know the properties, sorting of materials into groups is easy. Some of the properties that are discussed here are appearance, hardness, solubility, floating, and transparency.

(a) Appearance

copper

Materials are always different in their appearance and we can make out it from its texture and luster. Metal looks different from wood. Metals like gold, silver iron, copper, etc are lustrous. On exposure to air for a long period of time, iron and copper may become dull. But when it is freshly cut, it shines.

(b) Hardness

Certain objects around you can be compressed easily whereas other objects are difficult to compress. A sponge is easily compressible. You can make a mark on wood with an iron nail by scratching on it. That means iron nail is more hard than wood.

Materials that can be compressed or scratched easily are called soft material and materials which are not easy to compress are called hard materials.

soft sponge

hard rock

    (c) Solubility

You might have noticed that some of the objects dissolve completely in water and some of them do not dissolve. This is one of the important properties for sorting materials into groups. On dissolving salt or sugar in water, it gets soluble easily. If you are adding and mixing chalk powder in water, it may not be dissolving completely.

The substances that are completely dissolving are called soluble substances. Substances that do not mix with water and do not dissolve even after stirring are called insoluble substances.

Solubility is applicable to liquids and gases also. On mixing water and vinegar, it is easily miscible. But on mixing oil and water, we will get two separate layers. Some gases like oxygen are soluble in water. We know that aquatic living things are depending on dissolved oxygen in the water.

fish need oxygen

   (d) Floatation

ice floating

We have seen ice floating on water. Depending on the density, objects can float or sink. The object which is less dense will float. Ice is less dense than water. Similarly, a dry leaf thrown into a pond floats in water, while a stone sinks. When a few drops of honey are poured into a glass of water, it sinks.

 (e) Transparency

transparent glass

Can you see through these glass tumblers? Yes, they are transparent. Substances or materials through which things can be seen are called transparent materials. In our daily life, we come across many transparent materials.

frosted glass

When we are looking through frosted glass, we can not the other side clearly. It allows the light to pass through it partially. Such materials through which objects can be seen partially, not clearly are called translucent. You can think about more examples of this.

wooden plank

Are you able to see the other side when you look through these wooden logs? The materials like wood and metals will not allow the light to pass through it. Hence we can not see the other side. These materials are called opaque materials. List out more examples of opaque objects.

 So we can sort different materials into different groups based on the similarity of their properties. Grouping or sorting is done for our convenience. In shops, libraries, textile,s and even at home, we store different things by sorting things for our easy access. Grouping or sorting of materials into groups is helpful to study the properties of groups and to observe the pattern in these properties.

NCERT SCIENCE-CLASS 9-SEPARATION TECHNIQUES , IS MATTER AROUND US PURE-PART-2

IS MATTER AROUND US PURE? - PART-2 SEPARATION OF MIXTURES

In the first part, we have discussed element, compound, types of solution and mixtures. In this session, we shall discuss the various methods to separate the components of a mixture.

NCERT SCIENCE-CLASS 9-SEPARATION TECHNIQUES, IS MATTER AROUND US PURE-PART-2

Is matter around us pure? Substances which we see around us may not be pure always. In many instances, we have to separate the components present in a mixture. So we are using several separation techniques, In the case of a heterogeneous mixture, components can be separated by simple methods like handpicking, sieving, filtering, magnetic separation etc. 

In this session, we can see other methods of separation used in a homogeneous mixture and some special cases of heterogeneous mixtures.

1. Evaporation 

The evaporation process is used for separating sea salt from seawater, which you have studied in lower grades. The same process can be used for separating the volatile component (solvent) from its non- volatile solute.

INK

Example: Ink is a mixture of dye. To obtain dye particles from ink, few drops of ink can be heated on a watch glass. It should not be heated directly. By keeping the watch glass over a beaker containing water and by heating the beaker ink particles are obtained as a residue. You can refer to the diagram given in your textbook.

2. Centrifugation

How can we separate butter from buttermilk? You might have seen churner used for this purpose. Still, we are using churner to collect butter and we make ghee from it.

When the solid particles present in a liquid is very small in size, it will pass through the filter paper. Those mixtures can be separated by the separation techniques called centrifugation. 

CENTRIFUGE

The principle of centrifugation is that the denser particles are forced to the bottom of the centrifuging tube and the lighter component in the mixture will remain on top when it is spun at high speed.

Using this principle we can:

• separate butter from curd
• test blood and urine in the diagnostic lab
• squeeze out water from wet clothes in a washing machine.

3. Separating funnel

How can we separate oil from a mixture of oil and water? Two immiscible liquids can be separated based on its densities. The apparatus used for this separation technique is called separating funnel. By opening the stopcock of the separating funnel, we can pour out the lower layer carefully.

SEPARATING FUNNEL

4. Sublimation

How can we separate a white coloured ammonium chloride from a similar coloured common salt? The sublimation process can be used to separate a mixture containing a component which sublimes from a component which does not sublimes.

Ammonium chloride will undergo sublimation on heating, while common salt does not. On cooling it further, ammonium chloride will undergo deposition and it can be separated.

There are many other compounds like naphthalene and anthracene which can be separated by this method.

5. Chromatography

It is the separation technique for separating solutes that dissolve in the same solvent. This technique got its name from the Greek word Kroma which means colour. It was used for the separation of colours in dyes earlier. Using advanced technology, now we are using it in various fields like separating drugs from the blood.

DYE

A dye is a mixture of two or more colours mixed together. By chromatography, the coloured component that is more soluble in the water rises faster and gets separated. So depending upon the solubility different coloured components are seen on different zones.

6. Distillation

DISTILLATION

This is a very popular separation technique. Distillation is the method used to separate components of a mixture containing two miscible liquids that boil without decomposition. Each component should have sufficient difference in boiling point and it should be more than 25 K.The basic principles behind this is evaporation followed by condensation. The component which boils first will get evaporated first and is collected after condensing it.

Example: a mixture of acetone and water.

DISTILLATION

For mixtures with less than 25 K boiling point difference, fractional distillation is used. It is widely used in petroleum refineries to separate fractions of petroleum-like petrol, diesel, kerosene etc. Components of petroleum and different gases present in the air are separated by an advanced separation technique called fractional distillation.

fractional distillation

7. Crystallisation

Have you ever wondered how crystals are formed? Do you know how these beautiful crystals are made? 

Crystallisation is a method usually used to purify solids. It separates a pure solid component in the form of crystals from its solution leaving behind the impurities in it.

Example: Pure copper sulphate can be obtained from its impure sample by crystallisation. Salt from seawater is also purified by this method.

crystals

crystals

So depending upon the nature of the components present in a mixture, we can select various methods of separation. These separation technique has got much application in the manufacturing field of many substances.

 

NCERT science class 8- metals and non metals, chapter-4, notes

METALS AND NON-METALS CHAPTER-4 CLASS-8  

NCERT science class 8- metals and non-metals, chapter-4, notes

We are familiar with a variety of materials which are used in our daily life. In lower grades, we have classified materials based on its appearance, hardness, transparency and texture.

In this session, we will deal with a major classification of materials. 
Based on its physical and chemical properties we can classify materials like metals and non-metals.

Out of 118 elements discovered, the majority of them are metals and these elements are arranged in the periodic table to make our studies easier. Gold, silver, iron, copper and aluminium are some of the popular metals.

copper metal

PHYSICAL PROPERTIES OF METALS

• Metals are generally hard. But there are few soft metals like sodium and potassium which can be cut with a knife.
• Metals are generally solid. But mercury is a liquid metal at room temperature.
• Metals are lustrous- having a shining surface.
• Metals are malleable- It can be beaten into thin sheets. We are using aluminium foil and silver foil as thin sheets. 

• Malleability-It is the property of metals by which it can be beaten into thin sheets.
• Metals are ductile- It can be drawn into wires. Aluminium and copper wires are normally used in electrical cables and wires.           Ductility- It is the property of metals by which it can be drawn into wires.
• Metals are good conductors of heat and electricity.
• Metals are sonorous- makes a ringing sound when struck hard.
• Melting point and boiling points of metals are generally high.

aluminium foil

conductors of electricity

PHYSICAL PROPERTIES OF NON-METALS

• Non-metals are not hard and they exist as solid, liquid and gas. Solid- carbon, sulphur, phosphorus, liquid- bromine, gas- hydrogen, oxygen, nitrogen
• They are not malleable.
• They are not ductile.
• They are poor conductors of electricity and heat.
• They are generally dull except iodine.
• They are non- sonorous.
• Non- metals have a comparatively low boiling point and melting point.

CHEMICAL PROPERTIES OF METALS 

1.Reaction of metals with oxygen

Metals will react with oxygen to form their corresponding oxides.

Metal + Oxygen → Metal oxide

Magnesium burns with oxygen to form Magnesium oxide (white powder)

On dissolving magnesium oxide with water, it forms magnesium hydroxide which turns red litmus paper to blue.

Mg + O2 → MgO

MgO + H2O → Mg(OH)2

Similarly iron reacts with oxygen and water in the air to form an iron oxide which we commonly call as rust.

Fe + O2 + H2O → Fe2O3 .xH2O

RUSTED GATE

Copper reacts with air to form basic copper carbonate which is commonly called as verdigris(green coating).

Cu + O2 + H2O + CO2 → Cu(OH)2 + CuCO3

VERDIGRIS GREEN COATING

Metal oxides formed are generally basic in nature.

2. Reaction of metals with water

Different metals are reacting with water in different manners. Some react very slowly and some of them do not react at all. But metals like sodium and potassium react very violently with water. Hence they are stored in kerosene to prevent its reaction with water and other components in the air. 

Iron reacts very slowly with water. Noble metals like gold and silver do not react with water.

3. Reaction  of metals with acids

Metals react with acids to form metal salts and hydrogen.

Mg + HCl → MgCl2 + H2

The presence of hydrogen can be tested using a burning match stick. It burns with a pop sound when bought near the mouth of the test tube.
The reaction condition is different for different metals. Some react at room temperature, but some of them will react when warmed.

Copper reacts with sulphuric acid, but it does not react with hydrochloric acid even on heating.
Less reactive metals like silver and gold do not react with dilute acids.

4. Reaction with bases

Metals react with bases like sodium hydroxide to form hydrogen.

On dropping a strip of aluminium into sodium hydroxide solution, hydrogen gas is evolved which makes a pop sound on a burning match stick.

5. Displacement reaction

A more reactive metal can displace a less reactive metal from its compound in aqueous solution.

On placing an iron nail in blue coloured copper sulphate solution, it forms a green coloured iron sulphate solution and brown deposits of copper. Here iron being more reactive can replace copper from copper sulphate.

Fe + CuSO4 → FeSO4 + Cu

But copper is not able to replace iron as it is less reactive than iron.

copper sulphate

iron sulphate

Displacement reaction happens based on the reactivity series. It is the arrangement of metals in a vertical column in order of decreasing reactivity.

Reactivity series:

Potassium     (most reactive)

Sodium

Calcium

Magnesium

Aluminium 

Zinc

Iron 

Lead

Hydrogen

Copper

Mercury

Silver

Gold  (least reactive)

(mnemonics to learn reactivity series- please stop calling me a zebra, I like her calling me a smart goat- the first letter of metals)

CHEMICAL PROPERTIES OF NON-METALS

1. Reaction with oxygen

Certain non- metals with react with oxygen to form oxides and on dissolving with water, it forms acids. Hence non-metal oxides are acidic in nature.

For example, sulphur on burning with oxygen forms sulphur dioxide(SO2).On reaction with water, it forms sulphurous acid(H2SO3).

S + O2 → SO2

SO2 + H2O → H2SO3

2. Reaction with water

Non- metals are not reactive with water. Hence non-metals like phosphorus is stored in water to avoid the reaction with oxygen in the air. It is a very reactive non-metal and catches fire on exposure to air.

3.Reaction with acids

Non-metals are not reactive with acids generally.

4.Reaction with bases

The reaction of non-metals with bases are normally complex.

USES OF METALS

automobile

gate

rails

utensils

USES OF NON-METALS

fertilizer

for breathing

tincture iodine antiseptic

synthetic fibres and plastics class 8 extra questions, assertion reason type questions

SYNTHETIC FIBRES AND PLASTICS- IMPORTANT QUESTIONS

synthetic fibres and plastics class 8 extra questions, assertion reason type questions

FILL IN THE BLANKS:

1. Rayon is obtained by the chemical treatment of ---------

2. --------is the synthetic fibre used to make parachutes.

3. The synthetic fibre which resembles wool is -------

4. Polycot is a mixture of -------- and cotton.

5.The plastic which can be deformed easily on heating is known as ---------

6. ---------- is used to make handles of utensils.

7. A material which is not easily decomposed by natural processes are called --------

8. Plastics are ---------- of heat and electricity.

9. Uniforms of firemen have a coating of ---------- to make them flame resistant.

10. ----------- is used for non-stick coating on cookware.

ASSERTION-REASON QUESTIONS

Select the correct option for the following assertion-reason questions:

a. (A) is correct and (R) is the correct explanation of (A).

b. (A) is correct and (R) is not the correct explanation of (A).

c.(A) is correct and (R) is wrong.

d. (A) is wrong and (R) is correct.

1. Assertion(A): Bakelite is used for making electrical switches.

Reason(R): Bakelite is a poor conductor of electricity.

2. (A) Thermosetting plastics can not be remoulded.

(R) Thermosetting plastics can be softened on heating.

3. (A) Synthetic fibres are more popular than natural fibres.

(R) Synthetic fibres are more durable and less expensive.

4. (A) Nylon fibres can not be used for making ropes for climbers.

(R) Nylon fibres are very strong fibres.

5. (A) We should not use synthetic fabrics while working in the kitchen.

(R) Synthetic fabrics dry up quickly and are easy to wash.

SHORT ANSWER QUESTIONS:

1. Which fibre is called artificial silk? Why?

2. List five uses of nylon.

3. What are the uses of PET polymer?

4. What are the characteristics of synthetic fibres?

5. Differentiate thermoplastics and thermosetting plastics.

ANSWERS:

Fill in the blanks:

1. wood pulp

2. nylon

3.acrylic

4. polyester

5.thermoplastics

6. bakelite

7. non-biodegradable

8. poor conductors

9. melamine

10. teflon

Assertion-Reason type:

1. (a)

2. (c)

3. (a)

4. (d)

5. (b)