METALS AND NON METALS Notes for class 8

Class 08 CHAPTER -4    MATERIALS : METALS AND NON METALS

1) Occurrence of metals and non metals :-

Out of the 92 naturally occuringelements 70 are metals and about 22 are nonmetals. 

Some elements show properties of both metals and non metals. They are called metalloids.

•Only some metals like gold, silver, platinum etc are found in the free state. Most metals are found in the combined states as oxides, sulphides, carbonates, silicates etc.

•Some non metals are found in the free state like helium, neon, argon etc. and some are found in free and combined states like sulphur, phosphorus etc.

2) Metallurgy :-

•Metallurgy:-is science of extraction of metals from their ores and their purification.

•Minerals:-are naturally occuringsubstances containing one or more elements or their compounds.

•Ore:-is a mineral from which one or more metals can be extracted profitably.

•Metallurgical processes:-consists of three main steps. They are :-i) Concentration of the ore ii) Reduction iii) Refining

•Concentration of the ore:-is the removal of impurities from the ore.

•Reduction:-the process of obtaining the metal from its compound.

•Refining:-is the process of purification of the impure metals to obtain the pure metal.

3) Physical properties of metals and non metals:-

•Metals

•Metals are solids (except mercury).

•Metals are hard (except sodium, potassium etc.

•Metals have metallic lustre.

•Metals have high melting points and bolilingpoints.

•Metals are malleable ( can be made into thin sheets).

•Metals are ductile (can be made into thin wires).

•Metals are good conductors of heat and electricity.

•Metals are sonorus(produces sound).

•Non metals

•Non metals may be solids, liquids or gases.

•Non metals which are solids are brittle (diamond is the hardest).

•Non metals do not have lustresome have a dull luster.

•Non metals have low melting points.

•Non metals are not malleable.

•Non metals are not ductile.

•Non metals are bad conductors of heat and electricity (except graphite).

•Non metals are not sonorous

4) Chemical properties of metals and non metals:-

a) Reaction with oxygen:-

Metals react with oxygen to form metallic oxides. These oxides are  basic oxides because they react with water to form bases. Eg. Magnesium burns in air to form magnesium oxide. Magnesium  reacts with water to form magnesium hydroxide.

2 Mg + O2--à2 MgO

MgO+ H2O-à  Mg(OH)2

Non metals react with oxygen to form non metallic oxides. These  oxides are acidic oxides because they react with water to form  acids.

Eg. Sulphurburns in air to form sulphurdioxide. Sulphurdioxide  reacts with water to form  sulphurousacid.

S + O2->SO2

SO2+ H2O---> H2SO3

b) Reaction with water:-

Metals react with water to form metal hydroxides and hydrogen.

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

2 Na + 2 H2O--> 2 Na OH + H2

Magnesium reacts with water to form magnesium hydroxide and hydrogen.

Mg + H2O ---> Mg(OH)2+ H2

Non metals do not react with water.

c) REACTION WITH ACIDS:-

Metals react with acids to form metallic salts and hydrogen.

 Eg. Zinc reacts with dilute hydrochloric acid to form zinc chloride  and hydrogen.

Zn + 2 HCl -----> ZnCl2+ H2

Most non metals do not react with acids.

Some non metals like sulphur reacts with concentrated nitric acid to forn sulphur dioxide, nitrogen dioxide and water.

S + 4HNO3 ------> SO2+ 4 NO2+2 H2O

d) Metals replace metals:-

A more reactive metal replaces a less reactive metal from its salt  solution.

Eg. Magnesium replaces copper from copper sulphate solution to form magnesium sulphate and copper.

Mg + CuSO4---> MgSO4+ Cu

Zinc replaces copper from copper sulphate solution to for zinc sulphate and copper.

Zn + CuSO4-----> ZnSO4 + Cu

Iron replaces copper from copper sulphate solution to form iron sulphate and copper

Fe + CuSO4-----> FeSO4+ Cu

Based on the reactivity of metals, they can be arranged in the decreasing order of their activity.

5) Activity series of metals :-

The arranging of metals in the decreasing order of their reactivity is called activity series of metals.

In decreasindg order

Potassium

Sodium

Magnesium

Aluminium Decreasing

Zinc order of

Iron reactivity

Lead

Copper

Silver

Gold

6) Noble metals :-

Metals like gold, silver, platinum etc. retain their lustre because they do not react with air, water or acids. So they are called noble metals.

Gold dissolves in aqua regia. Aqua regia is a mixture of concentrated nitric acid and concentrated hydrochloric acid in the ratio 1:3.

Pure is 24 carat gold. It is very soft and cannot be used for making ornaments. So it is mixed with some silver or copper to make it hard.

7) Uses of metals :-

Iron :-is used for making pins, nails, nuts, bolts, tools,

machines, construction of buildings, bridges etc.

Aluminium :-is used for making utensils, wires, furniture,  parts of aircrafts, vehicles, machines, for packing food and medicines etc.

Copper :-is used for making wires, vessels, electric  gadgets etc.

Gold :-is used for making jewellery, coins medals etc

Silver :-is used for making jewellery. Coins, medals etc.

Platinum :-is used for making jewellery, electric gadgets, plugs in vehicles etc.

Sodium :-compounds are used as common salt,  chemicals etc.

Calcium :-compounds are used for making cement, glass etc.

8) Uses of non metals:-

Sulphur:-is used for making sulphuric acid, salts of  metals etc.

Oxygen:-is used for respiration by living things, burning  of fuels etc.

Nitrogen:-is used for making ammonia which is used for  making fertilizers.

Hydrogen:-is used for making ammonia which is used for making fertilizers, as fuel in rockets, for welding etc.

Chlorine:-is used to kill germs in water.

Iodine:-is used as tincture iodine which is an antiseptic

10) Corrosion:-

The surface of some metals gets corroded when exposed  to moist air for a long time. This is called corrosion.

Prevention of corrosion of metals:-

The corrosion of metals can be prevented by:-

i) Applying oil or grease.

ii) Applying paint

iii) Galvanisation ( coating of metals with non corrosive metals like zinc)

iv) Electroplating ( coating of metals with non corrosive metals like chromium tin by passing

electricity)

v) Alloying ( Eg. When iron is alloyed with chromium and nickel, it forms stainless steel which is resistant to corrosion) 

CBSE 8th Solved Question Ch: Combustion and Flame Extra Mark Gainer

Class 8th solved question Combustion and Flame

1. Chose the substances which will produce flame on burning and why?  Charcoal, molten wax, paper, coal, mustard oil.

Ans: molten wax and mustard oil.

2. Draw a well labeled diagram for the flame of a candle and answer the following

Questions:

(a) Which zone is luminous and why ?

(b) Why is the innermost zone grey in colour and the coldest zone ?

(c) Which zone is called the zone of complete combustion and why?

Ans: (a) inner most zone is luminous due to partial combution . The unburnt carbon particles impart a pale yellow colour to the flame.

(b) The innermost zone is grey in colour and the coldest zone because It contains unburnt gas particles. No combustion takes place here as no oxygen is available.

(c)Outer most zone is called the zone of complete combustion Here, carbon and hydrogen are completely oxidized to Carbon dioxide and water vapour.

3. Calorific value of wood is approx.17000-22000kj/kg .what does it mean?

Ans: when 1 kg  fue (wood)  is burnt completely in oxygen produce approx.17000-22000kj heat energy.

4. Why is it dangerous to burn coal in a closed room?

An: When coal burn  in a closed room produce toxic fumes or smoke or other harmful product .

5. Write any four characteristics of good fuel .

Ans: he main characteristics of a good fuel are :-

i) Is readily available and cheap. ii) Does not leave behind any undesirable substances.

iii) Is easy to store and transport.  iv) Burns at a moderate rate.

v) Produces a large amount of heat.    vi)  Does not cause pollution.

6. Name the gases which lead to formation of acid rain?

Ans: Oxides of sulphur and nitrogen dissolve in rain water and form acids. Such rain is called Acid Rain. It is very harmful for crops, buildings and soil.

7. In an experiment 10 Kg of a fuel produced 200,000 KJ 0f heat . Calculate the calorific value of the fuel

Ans: The calorific value of a fuel :- is the amount of heat energy produced on complete combustion of 1 kg of a fuel. The calorific valve of a fuel is expressed in kilo joule per kg.

The calorific value of the fuel = 200,000 KJ/10 Kg =200,00 KJ/kg

8. How does CO2 help in fire fighting?

Ans: Carbon dioxide is the best fire extinguisher to put out fire caused by inflammable materials like oil and petrol and electrical equipments. Carbon dioxide is heavier than air and it covers the fire and cuts off the supply of oxygen and puts out the fire.

9. What are the drawbacks of using solid fuel?

Ans: The drawbacks of solid fuels are as follows:

1. They have a high ignition temperature.

2. They produce a large amount of residue (soot, ash) after combustion.

3. Their calorific value is low.

10. What are the harmful effects on the environment due to burning of fuels?

Ans: i) Fuels like wood, coal, petroleum release unburnt carbon particles which cause respiratory diseases like asthma.

ii) Incomplete combustion of fuels release carbon monoxide gas which is a very poisonous gas which can cause death.

iii) Burning of most fuels release carbon dioxide gas which causes rise in the temperature of the atmosphere. This is called global warming. It causes melting of polar ice, rise in sea level and flooding of coastal areas.

CHAPTER - 6 COMBUSTION AND FLAME CBSE Notes for class 8th

Class 8th solved Question Combustion and Flame by Jsunil Tutorial

Class 8th solved question Combustion and Flame

1. Define Fuel. Give examples of solid, liquid and gaseous fuels.

Ans: The substance that undergoes combustion is called fuel. Fuels are substances which, on combustion produce heat energy without producing undesirable by-products.

Fuels are of three main types. They are :-

i) Solid fuels :- Eg:- wood, coal, charcoal etc.

ii) Liquid fuels :- Eg:- kerosene, petrol, diesel etc.

iii) Gaseous fuels :- Eg:- CNG, LPG, biogas, hydrogen etc.

2. Differentiate between combustible and non-combustible substances with two examples of each kind?

Ans: Combustible substances:- Substances which burn in air to produce heat and light are called combustible substances.  Eg :- wood, coal, charcoal, kerosene, petrol, diesel, liquified petroleum gas (LPG), compressed natural gas (CNG) etc.

Substances like stone, glass, iron nails, etc. do not burn on being exposed to flame. Such substances are called non-combustible substances.

3. What is combustion?

Ans:  Combustion: - The chemical process in which a substance reacts with oxygen to produce heat is called combustion.  Combustion is the burning of substances in air or oxygen to release heat and light.

e.g. magnesium burns to form magnesium oxide and produces heat and light.

4. Why does a candle stop burning when covered with a glass tumbler?

Ans: A candle stop burning when covered with a glass tumbler due to absence of oxygen that support burning. Air is necessary for combustion.

5. How is spontaneous combustion different from explosion?

Ans: Spontaneous combustion:- is combustion in which a substance burns spontaneously and produces heat and light without the help of external heat. Eg:- phosphorus burns spontaneously at room temperature

Explosion:- is a combustion in which a substance burns suddenly and produces heat, light and sound with the help of heat or pressure. Eg:- explosion of crackers on applying heat or pressure.

6. Special care should be taken to store kerosene oil. Give reason.

Ans: kerosene oil is combustible substance and produce heat and light immediately so Special care should be taken to store kerosene oil.

7. When the clothes of a person catch fire, the person is covered with a blanket to extinguish the fire. Can you guess why?

Ans: Blanket cut off supply of air or oxygen to extinguish the fire

8. Why is L.P.G labeled as inflammable substance?

Ans:  L.P.G has low ignition temperature and catches fire easily so L.P.G labeled as inflammable substance.

9. Which substance added to LPG to detect any leakage?

Ans: A small amount of ethyl mercaptan, an inert gas with a characteristic odour, is added to LPG to detect any leak.

10. How does water help to extinguish fire?

Ans:  When water is poured over a burning substance, it absorbs heat from the substance. As a result the temperature of the substance falls below the ignition temperature, and it stops burning

CHAPTER - 6 COMBUSTION AND FLAME CBSE Notes for class 8th

8th Combustion and Flame CBSE Test Paper

Science CLASS – VIII COMBUSTION AND FLAME
Q.1 Name a few fuels used in our homes.
Q.2 Name a few fuels used in trade and industry.
Q.3 What fuels are used for running automobiles?
Q.4 What is the difference between the burning of a candle and burning of a fuel like coal?
Q.5 What is combustion?
Q.6 Define a fuel?
Q.7 (i) What are the essential conditions required for combustion?
(ii) What is the essential condition required for extinguishing fire?
Q.8 What are inflammable substances?
Q.9 In what form is LPG stored in cylinders?
Q.10 Name the most common fire extinguisher?
Q.11 Water is not suitable for extinguishing fires involving electrical equipment oil and petrol. Why?
Q.12 Explain how CO2 is able to control fires?
Q.13 What are the requisites (qualities) of a good (ideal) fuel?
Q.14 Explain the following terms:-
(i) Global warming
(ii) Acid rain

Q.15 Suppose you are asked to boil a given quantity of water using cow dung  cake, coal and LPG as fuels. Which fuel would you prefer? Give your reason.
Q.16 Define calorific value of a fuel. Though hydrogen has got highest calorific value but it is not used as a domestic fuel. Why?
Q.17 Make a labeled diagram of a candle flame.
Q.18 Name various types of combustion. Give example of each type?
Q.19 Differentiate between.
      (a) Combustible and non combustible substances
      (b) Complete combustion and incomplete combustion.
      (c) Luminous and Non-luminous flames.
Q.20 Define the term ignition temperature. Why substances like alcohol and petrol are called inflammable substances? 

8th Chemical reactions

Question:  1-Define the following terms- (Write equations to support your answer)

i. Chemical reaction

ii. Exothermic reaction

iii. Decomposition reaction

iv. Oxidation reaction

Question:  2- Write down two characteristics of chemical reaction.

Question:  3- Balance the following equations-

(i) H2 + O 2 à H2O

(ii) Mg + O2 à MgO

(iii) N2 + H2 àNH3

(iv) H2S + Cl2 àS + HCl

Question:  4- Write the formula of the following-

(i) Magnesium hydroxide

(ii) Sodium carbonate

(iii) Silver nitrate

(iv) Iron sulphate

Question: 5- Fill in the blanks-

(i) When two chemicals in a solution form react, and an insoluble substance is formed and settles down in the form of __________.

(ii) Heat is absorbed in _____________ reactions.

(iii) The formula of rust is _________.

CBSE Class 7 Solved Objective Questions Chapter - Acids, Bases and Salts (MCQs)

CBSE Class 7 Solved Objective Questions  Chapter - Acids, Bases and Salts MCQs

1. The word acid comes from the Latin word ------ which means sour.( acere)

2. The substances used to test whether a substance is acidic or basic are known as ----(indicators)

3. The most commonly used natural indicator is litmus paper . It is extracted from ----(lichens)

4. In acidic solution, litmus paper turns into ------(red)

5. In basic solution, litmus paper turns into ------(blue)

6. In distilled water , litmus paper turns into ------(purple)

7. China rose indicator turns acidic solutions ------and basic solutions to ------ [dark pink (magenta) , green]

8. The reaction between an acid and a base is known as ----- [neutralization]

9. Salt and water are produced in neutralization process with the evolution of heat.[ water]

10. H C l + N a O H ---->      ------- + H2O

11. Our stomach contains -------. It helps us to digest food[hydrochloric acid]

12. indigestion is painful so to relieve indigestion, we take an antacid such as milk of magnesia , which contains ------- [magnesium hydroxide]

13. The sting of an ant contains ---------[ formic acid]

14. The effect of the sting can be neutralized by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains ------- [zinc carbonate]

15. When the soil is too acidic, it is treated with ---------------[ bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide)]

16. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. its nature ---------------------- [Basic]

17. The wastes of many factories contain-------- [ acids]

18. Blue litmus paper is dipped in a solution. It remains blue. -------- is the nature of the solution. [basic]

19. Proteins that build part of our cells are made up of------ [amino acids]

20. The fats in our body contain ------ [fatty acids]

21. Each cell in our body contains an acid called ---------- [the deoxyribonucleic acid]

22. ----------- is common to all acids?[hydrogen ion]

23. ------ gas evolved when dilute sulphuric acid acts on sodium carbonate[CO2]

24. Acids do not show acidic behavior in absence of water because ------ dissociates from an acid only in in presence of water .[ hydrogen ions]

25. ---- base is also used in soda-acid fire extinguishers.[ Baking Soda]

26. -------- gas is usually liberated when an acid reacts with a metal [ H2]

27. The hydrogen ions combine with H2O to form ------------- [ hydronium ions (H3O+)]

28. Aqueous solution of acid conduct electricity due to -------- present in it. [ ion]

29. ------------ is the common name of the compound CaOCl2 [Bleaching powder]

30. -------------- is Universal Indicator [ pH Scale]

31. pH is the measure of Acidity or Alkalinity of a solution. The term pH stands for ----------[“Potential of hydrogen”]

32. If the pH rain water drops below ----------------. it is called acid rain[5.6]

33. The bases that dissolve in water are known as -----------[ alkalies]

34. Aqueous solution of sodium chloride (NaCl) is known as -------------[ Brine]

35. Salts containing water molecules in their crystal form are called --------- [hydrated salts]

36. water molecules present in salt s known as ------------ [‘water of crystallization’]

37. Phenolphthalein become colourless in ---- and pink in ------[ Acid, base]

38. --------- is the colour of methyl orange in acidic solution.[ pink]

39. ------------ and ------- acid are present in vinegar and lemon.[ acetic acid, citric acid]