CBSE ADDA

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 remo

CHAPTER - 6 COMBUSTION AND FLAME Ncert Notes for classs 9th 1) 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. 2) Combustion :- The chemical process in which a substance reacts with oxygen to produce heat is called combustion. The substance which undergoes combustion is called a combustible substance. It is also called a fuel. Air is necessary for combustion. Sometimes light is also produced during combustion either as a flame or as a glow. 3. Ignition temperature :- The minimum temperature at which a substance catches fire and burns is called its ignition temperature. A substance will not catch fire and burn if its temperature is lower than its   ignition temperature.  Different substances have different ignition temperatures.  Eg:- The ignition temperature of kerosene is less than t

Q.1: Which separation techniques will apply for the separation of the following? (a) Sodium chloride from its solution in water. (b) Ammonium Chloride from a mixture containing Sodium Chloride and Ammonium Chloride. (c) Small pieces of metal in the engine oil of a car.    (d) Different pigments from an extract of flower petals. (e) Butter from curd. (f) Oil from water. (g) Tea leaves from tea. (h) Iron pins from sand. (i) Wheat grains from husk. (j) Fine mud particles suspended in water. Ans: (a) Crystallization or Evaporation. (b) Sublimation. (c) Centrifugation or Sedimentation. (d) Chromatography. (e) Centrifugation. (f) Separating funnel. (g) Hand-picking. (h) Magnetic separation. (i) Winnowing. (j) Centrifugation. Q.2: Write the steps you would use for making tea. Use the words - solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue. Ans: Take the solvent, water, in a kettle. Heat it. When the solvent boils, add the solute, milk. Milk and water forms a

  Chapter 2 . Acids, Base and Salts 1. A milkman adds a very small amount of baking soda to fresh milk 2. Why do acids not show acidic behaviour in the absence of water? 3. Alcohols and Glucose contain hydrogen but are not categorized as acids. 4. Plaster of Paris should be stored in a moisture-proof container. Explain why? 5. Why is calcium sulphate hemihydrates called 'Plaster of Paris'? 6. Equal lengths of the magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH 3 COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why? 7. Name a solution reacts with crushed egg-shells to give a gas that lime-water milky. 8. Why does distilled water not conduct electricity, whereas rain water does. 9. What is aqua-regia ? 10. Name the sodium compound which is used for softening hard water. 11. Why should curd and sour substances not be kept in brass and copper vessels? 12. What