Physical and Chemical Changes
• Physical changes are the change which only affect the physical properties like colour, hardness, density, melting point etc of matter but do not affect the composition and chemical properties of matter.
• Crystallisation, sublimation, boiling, melting, vaporisation, cutting of trees, dissolving sugar or salt in water etc are physical changes.
• Chemical changes affect the composition as well as chemical properties of matter and result in the formation of a new substance.
• Burning of fuel, burning of candle and paper, electrolysis of water, photo- synthesis, ripening of fruits etc are examples of chemical changes.
• Burning of candle involves both physical and chemical change.
Boiling Point
• It is the temperature at which the vapour pressure of a liquid becomes equal to the atmospheric pressure.
• The boiling point increases in the presence of impurities. That's why boiling point of sea water is more than the boiling point of pure water (as the former contains impurity).
• At high altitudes, the atmospheric pressure is less than sea level and hence, water boils at a lower temperature (less than 1000C) and food takes more time to cook.
• Inside the pressure cooker, pressure is higher and hence, water boils at a higher temperature (i.e., boiling point o water increases) and food is cooked quickly.
• The air éscaping from a punctured tyre is cold because the air escapes from a region of high pressure to low pressure.
Atom, Molecule and Element
• Atom is the smallest part of a matter that takes part in chemical reactions but cannot exist in free state.
• Atom is made up of electron, proton and neutron. Protons and neutrons reside in the nucleus (at the centre of atom) whereas electrons revolve around the nucleus. Atoms combine to form molecules, the smallest part of matter which can exist in free state.
• Element contains only one type of atoms. e.g., carbon (C), sulphur (S), diamond, graphite etc.
Isotopes and Isobars
• Isotopes have the same number of protons (i.e., atomic number) but different number of neutrons and mass number (atomic number + number of neutrons), e.g., 1H 1 , 1H 2 , 1H 3
• Isobars have the same mass number but different atomic number. e.g., 18Ar 40 , 19K 40 , and 20Ca 40.
Dating Techniques
• Radiocarbon dai.ing is used go determine the age of carbon bearing material? like wood, fossil etc.
• Uranium dating is used to determine the age of earth minerals and rocks.
Colloids
• These are heterogeneous solutions, containing two phases dispersed phase and dispersion medium.
• These show Tyndall effect (i.e., scattering of light by colloidal particles) and Brownian motion.
• Colloids can be dispersion medium loving (i.e., lyophilic) dispersion medium hating (i.e., lyophobic). Lyophilic colloids are more stable and reversible in nature.
• Dialysis a technique to purify colloids is used to purify blood with the help of artificial kidney machine.
Battery
• Battery is a device, used to convert chemical energy into electrical energy and is of two types
• Primary batteries (non-rechargeable) act as galvanic cell, e.g., dry cell, mercury cell etc.
• Secondary batteries (rechargeable) act as galvanic as well as voltaic cell e.g., lead storage battery, nickel- cadmium battery etc.
• In electrolytic refining, anode is made by impure metal anda strip of pure metal acts as cathode.
Corrosion
• The oxidative deterioration of a metal surface by the action of environment is called corrosion, an electrochemical process
• When exposed to air, iron surface turns brown due to the formation of hydrated ferric oxide (Fe203 • xH20) which is also called rust, silver surface turns black due to the formation of silver sulphide (Ag2S) and copper and bronze surfaces turn green due to the formation of basic copper carbonate,
• Corrosion of iron is called rusting and is accelerated by the presence of impurities, H+, electrolyte such as NaCl and gases like C02, S02, N02 etc.
• Corrosion is prevented by electroplating, by applying oil, grease, paint, varnish etc or by galvanisation (i.e., deposition of zinc layer over iron articles).
• A sliced apple, when exposed to air, turns brown after sometime. This is because apple contains iron which gets oxidised and gives a brownish colour to apple.
Renewable and Non-renewable Natural
Resources
• Renewable resources are available in large excess, i.e., never ends, e.g, air, sunlight etc.
• Non-renewable resources are available in limited quantity and end, if used excessively, after a limited period of time.
e.g., mineral, coopetroleum, natural gas etc.
Fuels
• The substances which produce heat and light on combustion are called fuels. A strong foul smelling substance, called ethyl mercaptan, C2H5SH, is added to LPG to detect its leakage as LPG is an odourless gas.
• The amount of heat obtained when lg of a fuel is burned in excess of oxygen is called calorific value.
• Vehicle carrying inflammable substances, have metallic ropes touching the ground during motion in order to provide earthing for lightning. Fuels used in rocket are called rocket propellants. A mixture of liquid hydrogen and liquid oxygen, is most common rocket propellant.
Coal
Coal is obtained by carbonisation of vegetable matter and is available in different varities : Peat (60% C), lignite or brown oal (70% C), bituminous coal (80% C), anthracite coal (90%C). ut of these, bituminous is the most common form.
Flame
Flame contains three parts
(i) Innermost part which is black due to the presence of unburned carbon particles—has lowest temperature.
(ii)Middle part is yellow due to incomplete combustion of fuel.
(iii)Outermost part which is blue due to complete combustion of fuel, is the hottest and used by goldsmith to heat the gold.
Fire Extinguishers
• Water is the most common fire extinguisher, i.e., used to extinguish fire.
• Water extinguishes fire because as it evaporates, the vapours surround the burning substance, cutting off the oxygen supply, thus inhibiting burning process.
• Hot water will extinguish fire more quickly than cold water as hot water will evaporate faster. in case of electrical or oil (Petrol) fires, water cannot be used as extinguisher. This is because water is a conductor of electricity and heavier than Oil. Thus, oil floats over it and continues to burn.
• Carbon dioxide, which is generated by the reaction of baking soda with acid, is used to extinguish electrical or oil fires.
• Quality of petrol is measured in terms of octane number and that of diesel in terms of number. TEL (Tetra Ethyl Lead) is an antiknock compound.
Safety Match
• In safety match, the stick consists of a mixture of antimony trisulphide and potassium chlorate at its one end. The box side contains a mixture of powdered glass and red phosphorus.
Acids and Bases
•Acids turn blue litmus red and gives proton (H+ ) in water.
•Bases turn red litmus blue and accept proton (H+ ) from other substances.
•pH is the measure of acidityfbasicity.
•pH of some important substances are
•Gastric juice 1.0 to 3.0
•Urine (Human) 4.8 to 8.4
•Saliva (Human) 6.5 to 7.5
•Tears 7.4
•Milk (Cow) 6.3 to 6.6
•Sea water 8.5
Inorganic and Organic Chemistry
Carbon Dioxide
It is an acidic oxide of carbon and is used by green plants for photosynthesis. It does not help in burning.
▪︎ Air and our breath contain carbon dioxide. Thus, when lime water is kept in air or we pass our breath into it, the lime water turns milky.
▪︎ When 'ENO' is dissolved in water, there appears effervescence due to liberation of carbon dioxide gas.
Carbon Monoxide
It is a neutral oxide of air and hag more affinity towards haemoglobin than oxygen (about 200 times more). That's why in the environment of carbon monoxide—which is a non-poisonous gas—people die for the need of oxygen.
Plaster of Paris
•It is chemically calcium sulphate hemihydrate (CaSO4 —1/2 H20) and is prepared by heating gypsum—which is calcium sulphate dihydrate (CaSOc 2H20)—-at 373 K.
•On mixing with water, plaster of Paris further sets into a hard solid, called gypsum. Thus, it is used to plaster factured bones, for making toys, materials for decoration and for making surfaces smooth.
Heavy Water
Heavy water is deuterium oxide (D20), its molecular mass is 20. It is called heavy due to the presence of deuterium, the heavy hydrogen.
Portland Cement
It is a complex mixture of silicates and aluminates of calcium with small amount of gypsum. Raw material used for the manufacture of Portland cement are limestone and clay.
The composition of Portland cement is calcium oxide (50-60%), alumina (5-10%), and magnesium oxide (2-3%) Gypsum is added to cement to decrease its rate of setting.
In cement, if lime is in excess, cement cracks during getting and if lime is less, cement is of weak strength.
Mortar a mixture of sand, cement and water is used for joining bricks and plastering walls. Concrete—a mixture of gravel, sand, cement and water is used for flooring and making roads. Reinforced Concrete (RC)—which is concrete with steel bars and wires is used for constructing roofs, bridges and pillars.
Glass
Glass—an amorphous solid or super- cooled liquid——contains mainly silica (Si02).
Different substances are added to obtain glass of different colours e.g.,
Hard Water
The water in which soluble bicarbonates of calcium magnesium are present, is called temporary hard and in which soluble sulphates and chlorides of magnesium and calcium are present is called permanent hard
The temporary hardness of water is removed by boiling or by adding calcium hydroxide, Ca(OH) —the Clark's process.
The permanent hardness of water is removed by adding sodium carbonate (Na2C03), or calgon (sodium hexameta_ phosphate, or zeolite— which is also called Permutit (hydrated sodium aluminium silicate Na2A12Si208.xH20).
Pesticides
These hemicals are used to destroy the organisms that harm the crop . These are of following types
Insecticides e.g., DDT, gammaxane, aluminium phosphate.
Fungicides e.g., Bordeux mixture, organo- mercury compounds.
Herbicides e.g., Benzipam, sodium chlorate.
Rodenticide e.g., Aluminium phosphide.