The biogas is then burnt as fuel (Change − B). Anaerobic bacteria digest animal waste and produce biogas (Change − A). (iv) None of these processes is a chemical change. (iii) Both processes A and B are chemical changes. The following statements pertain to these changes. When it comes out from the cylinder it becomes a gas (Change − A) then it burns (Change − B). The gas we use in the kitchen is called liquefied petroleum gas (LPG). Therefore, rusting of iron objects is faster in coastal areas than in deserts. In desert areas, the amount of moisture in air is even lower. In coastal areas, the quantity of moisture present in air is more than that in deserts. Both air and moisture are required for rusting to take place. Explain why rusting of iron objects is faster in coastal areas than in deserts.Īns. By painting an iron gate, we prevent its contact from the air and moisture present in the atmosphere. Rusting is aided by both moisture (water) and air (oxygen). Explain how painting of an iron gate prevents it from rusting.Īns. Slowly, the crystals of copper sulphate separate out. It is then filtered into a china dish and allowed to cool. ![]() Copper sulphate powder should be added on till the solution becomes saturated. The water is then heated and when it starts boiling, copper sulphate powder is added with stirring. Few drops of dilute sulphuric acid are added to this. Crystals of copper sulphate are prepared by the method of crystallization. Describe how crystals of copper sulphate are prepared.Īns. However, when we cut wood, only the shape and size of the wood are changed. When we burn wood, a new substance, coal, is formed. Explain why burning of wood and cutting it into small piece are considered as two different types of changes.Īns. Since these are the properties of a chemical change, setting of curd is a chemical change. ![]() Also, both milk and curd have different properties. Once the curd is formed, milk cannot be re-obtained from it. How would you show that setting of curd is a chemical change?Īns. Physical change → Breaking down of larger food particles into smaller particles When a candle burns, both physical and chemical changes take place.Įating of food is another example where both physical and chemical changes occur simultaneously. Give another example of a familiar process in which both the chemical and physical changes take place.Īns. When a candle burns, both physical and chemical changes take place. Lemon juice( Citric acid) + Baking soda (Sodium hydrogen carbonate) → Carbon dioxide + Other substances In this change, citric acid contained in lemon juice reacts with sodium hydrogen carbonate which results in the evolution of carbon dioxide gas. The bubbles are formed due to the evolution of carbon dioxide gas. When baking soda (Sodium hydrogen carbonate) is mixed with lemon juice (citric acid), bubbles are formed. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. (e) Changes in which new substances are formed are called chemical changes. (d) Changes in which only physical properties of a substance change are called physical changes. (c) Two methods by which rusting of iron can be prevented are galvanization and painting. (b) The chemical name of baking soda is sodium hydrogen carbonate. (a) When carbon dioxide is passed through limewater, it turns milky due to the formation of calcium carbonate (CaCo 3) (e) Changes in which new substances are formed are called _changes.Īns. (d) Changes in which only _ properties of a substance change are called physical changes. (c) Two methods by which rusting of iron can be prevented are _and (b) The chemical name of baking soda is _. (a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _. Fill in the blanks in the following statements: (True/False)Ĭutting a log of wood into pieces is a physical change.įormation of manure from leaves is a chemical change. (e) Condensation of steam is not a chemical change. (d) Iron and rust are the same substances. (c) Iron pipes coated with zinc do not get rusted easily. (b) Formation of manure from leaves is a physical change. (a) Cutting a log of wood into pieces is a chemical change. In case a statement is false, write the corrected statement in your notebook. State whether the following statements are true or false. (e) Beating aluminium to make aluminium foil → Physical change (b) Dissolving sugar in water → Physical change (e) Beating aluminium to make aluminium foilĪns. Classify the changes involved in the following processes as physical or chemical changes:
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