CHEMISTRY- AIR AND ATMOSPHERE CLASS VII

Transcription

1 CHEMISTRY- AIR AND ATMOSPHERE CLASS VII Q1. Explain the following terms. 1. Catalyst: A catalyst is a chemical substance that alters the rate of a chemical reaction without undergoing any chemical change itself. 2. Green-house effect: The phenomenon by which the sun s radiation reflected from the earth s surface is trapped by the gases in the lower atmosphere is called as green-house effect. 3. Global warming: The accumulation of green-house gases causes the atmosphere of the earth to heat up. This is known as global warming. 4. Acid rain: Rain that contains acids such as sulphuric acids, nitric acid, and carbonic acid is called as acid rain. 5. Air pollutant: Undesirable gases and particles present in the air that can have harmful effect on plants and animals are called as air pollutant. 6. Rusting: When iron comes in contact with atmospheric oxygen and moisture overtime, reddish-brown layer of hydrated ferric oxide (also known as rust) form on it. This process of formation of rust is called as rusting. Q2. Give reasons: 1. Air is called as mixture. Ans: The concentration of components of air is NOT FIXED at all places, hence air is a mixture. 2. Nitrogen is used for packing food items. Ans: Nitrogen is used for packing food items because it is inert i.e. it is highly stable in its diatomic form. 3. Carbon dioxide is used in fire extinguisher. Ans: Carbon dioxide is neither combustible nor does it support combustion. Hence it is used in fire extinguisher. 1

2 4. On adding vinegar to a dough containing baking soda, the dough becomes light and rises. Ans: Baking soda contains carbonate and vinegar contains acetic acid. The carbonate reacts with the acid to produce carbon dioxide. The carbon dioxide formed escapes out from the pores of the dough, making it rise. Q3. Distinguish between the following: 1. Slow oxidation and Rapid oxidation Slow oxidation The type of oxidation that is very slow and the energy released is negligible is called as slow oxidation. Eg: rusting of iron. Rapid oxidation/combustion The type of oxidation in which oxygen reacts very quickly with a substance with the release of heat and light energy is called as rapid oxidation. Eg: wood, coal, petrol, kerosene, LPG and candle wax. 2. Combustion and Rusting Combustion The type of oxidation in which oxygen reacts very quickly with a substance with the release of heat and light energy is called as rapid oxidation. Rapid oxidation Eg: Burning of wood, coal, petrol, kerosene, LPG and candle wax. Rusting When iron comes in contact with atmospheric oxygen and moisture overtime, reddish-brown layer of hydrated ferric oxide (also known as rust) form on it. This process of formation of rust is called as rusting. Slow oxidation Eg: rusting of iron lock, nail, etc. 3. Respiration and Combustion Respiration The process by which food (glucose) is broken down to release energy is called as respiration. Cellular process Energy is released as ATP Occurs at body temperature Combustion The type of oxidation in which oxygen reacts very quickly with a substance with the release of heat and light energy is called as rapid oxidation or combustion Non-cellular process Energy is released as heat and light Occurs at high temperature Q4. What are the uses of nitrogen? OR Give any 3 uses of nitrogen. It is used as preservative to preserve food such as potato chips. Liquid nitrogen is used as refrigerant for freezing food. It is used in preparation of ammonia by Haber-Bosch process. 2

3 Nitrogen is used to manufacture nitrogenous fertilizers such as AMMONIUM NITRATE (NH4NO3) Nitrogen is used in making explosives like Trinitrotoluene (TNT), Nitrocellulose, and Trinitroglycerine. Nitrogen is used in dyeing industries for making dyes that are used to colour fabric. Q5. Name the process for preparation of ammonia. Give the chemical equation for the reaction of nitrogen with hydrogen. Ans: Haber-Bosch process. Q6. Give the balanced chemical and word equation for the decomposition of the following: 1. Hydrogen peroxide (H2O2) 2. Potassium chlorate (KClO3) Q7. What happens when? a. Carbon dioxide is bubbled in lime water- it turns lime water milky due to formation of calcium carbonate which is milky. b. Carbon burns in excess of air- Carbon dioxide is formed. c. Phosphorus burns in excess of air- phosphorus pentoxide is formed. d. Sulphur burns in air- sulphur dioxide is formed. Q8. State any two physical properties of oxygen. Ans: Colourless, tasteless and odorless gas Slightly heavier than air. More soluble in water than nitrogen. 3

4 Neutral to litmus. Q9. Give the balanced chemical and word equation for the laboratory preparation of oxygen. i. From hydrogen peroxide. ii. From potassium chlorate. Q10. Observe the figure and answer the following questions: i. Identify and name the labels A, B, C, D and E. ii. What is the role of C in this process? iii. Why is the D produced in this process collected over water? Ans: i. A- Dropping funnel, B- Hydrogen peroxide, C- Manganese dioxide, D- Oxygen, E- Water. ii. iii. C- Acts as a catalyst. The D produced in this process collected over water because it insoluble in water and is lighter than water. Q11. Give the balanced chemical and word equation for the reaction of following metals with oxygen. i. Sodium Sodium + Oxygen Sodium oxide 4Na + O2 2Na2O 4

5 ii. iii. iv. Calcium Calcium + Oxygen Calcium oxide 2Ca + O2 2CaO Magnesium Magnesium + Oxygen Magnesium oxide 2Mg + O2 2MgO Potassium Potassium + Oxygen Potassium oxide 2K + O2 2K2O Q12. Give any two uses of Oxygen. Ans: It is used in Oxy-acetylene torch or oxy-hydrogen torch for welding and cutting metals. It is used in manufacture of iron and steel. In blast furnace, oxygen is used to extract iron from its ore. Q13. Give the word equation to show the renewal of oxygen in the atmosphere. Q14. Give the uses of carbon dioxide. Ans: In making aerated drinks- carbon dioxide dissolves in the water forming carbonic acid. As a dry ice, a solid form of carbon dioxide acts as a good refrigerant. In making fertilizer. Carbon dioxide is neither combustible nor does it support combustion. Hence it is used in fire extinguisher Green plants use carbon dioxide for carrying out photosynthesis. Q15. Name the air pollutants responsible for causing acid rain. Ans: Sulphur dioxide, carbon dioxide and oxides of nitrogen. 5

6 Q16. Give any two effects of acid rain. Ans: Acid rain damages the heritage buildings like the Taj Mahal. The stone of Taj Mahal is made up of limestone (CaCO3) which reacts with the acid in rain and corrodes them. It makes the soil and water bodies acidic thereby affecting plants and animals. Q17. What is air pollution? Give man-made and natural causes of air pollution (any two for each). Ans: The release of air pollutants into the air through unwanted human activities or natural process is called as Air pollution Man-made causes of air pollution: Exhaust from automobiles, thermal power plant and industries. Deforestation Burning of fossil fuels, incomplete combustion of fuels. Use of chlorofluorocarbon for refrigeration and air conditioning. Natural causes of air pollution: Volcanic eruptions Forest fires Release of Methane gas from marshes Q18. Give any four methods to reduce air pollution. Ans: Reducing the use of fossil fuels by following steps such as use of public transport and by switching off motor vehicles at red lights. Use of wet scrubbers in factories to absorb sulphur dioxide from exhaust. Planting more trees i.e. afforestation to remove excessive carbon dioxide from air. Avoid burning of polythene especially plastics. Keeping residential areas away from factory areas. ************************************************************************ 6