![]() ![]() It is a chemical change as it cannot be brought back to its original form.ġ9. Why is spoiling of food a chemical change?Īnswer: Spoiling of food is an unwanted quality change in a foodstuff, such as staling, discoloration, the development of off-flavours and odours. ![]() Magnesium oxide (MgO) + Water (H 2O) → Magnesium hydroxide ġ8. This change can be written in the form of the following equation: ![]() What happens when magnesium oxide is dissolved in water?Īnswer: On dissolving the magnesium oxide in water it forms a new substance. Why tearing of paper into pieces is a physical change?Īnswer: Tearing of a paper is a physical change because when the paper is torn only the shape and size of the paper is changed, no new substance is formed.ġ7. Iron (Fe) + Oxygen (O 2, from the air) + water (H 2O) → rust (iron oxide Fe 2O 3)ġ6. Write down the equation representing the process of rusting.Īnswer: The process of rusting can be represented by the following equation: Why a slice of an apple acquires a brown colour if it is not consumed immediately?Īnswer: A slice of an apple acquires a brown colour if it is not consumed immediately due to the formation of new substances.ġ5. A chemical change is also called a chemical reaction.ġ4. Why does rusting takes place faster during rainy season?Īnswer: Rusting takes place faster during rainy season because the content of moisture in air is high in rainy season.Īnswer: Properties such as shape, size, colour and state of a substance are called its physical properties.Īnswer: A change in which a substance undergoes a change in its physical properties is called a physical change.Īnswer: A change in which one or more new substances are formed is called a chemical change. Why a wet iron pan often gets rusted if left in that state for some time?Īnswer: A wet iron pan (tawa) often gets rusted if left in that state for some time because iron rust in the presence of oxygen and water.ġ0. Which technique is better for obtaining sugar from sugar solution?Īnswer: Crystallization is considered as a better technique for obtaining sugar from sugar solution.Īnswer: Large crystals of pure substances can be formed from their solutions. What happens when baking soda is treated with vinegar?Īnswer: Vinegar (Acetic acid) + Baking soda (Sodium hydrogencarbonate) → Carbon dioxide + other substancesħ. Name the two methods by which rusting of iron can be prevented.Īnswer: Two methods by which rusting of iron can be prevented are by painting or greasing and by galvanizing.Ħ. So, it is commonly known as blue vitriol.ĥ. This substance is called rust.Īnswer: Crystals of copper sulphate pentahydrate are blue in colour. Why souring of milk is a chemical change?Īnswer: Souring of milk is a chemical change because it results in formation of new substance.Īnswer: If a piece of iron is left in the open for some time, it acquires a film of brownish substance. Why formation of manure from leaves is a chemical change?Īnswer: Formation of manure from leaves is a chemical change because manure formed has a different composition from leaves.Ģ. What is added to steel to make it stainless?Īnswer: Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese. State the conditions necessary for rusting of iron?Īnswer: For rusting, the presence of both oxygen and water (or water vapour) is essential.Īnswer: The process of depositing a layer of metal like zinc or chromium on iron is called galvanisation.ġ1. What do you understand by chemical change?Īnswer: A change in which one or more new substances are formed is called a chemical change.ĩ. Which of the two is permanent change chemical change or physical change?Īnswer: Chemical change is a permanent change.Ĩ. ![]() What type of change is formation of manure?Īnswer: Formation of manure is a chemical change.ħ. What type of change is involved in rusting of iron?Īnswer: Rusting of iron is a chemical change.ĥ. What type of change is crystallisation?Ĥ. Physical and Chemical Changes Class 7 Science Extra Questions and Answers Very Short Extra Questions and AnswerĪnswer: The process of depositing a layer of zinc over iron is called galvanisation.Īnswer: The formation of rust over the surface of iron is known as rusting.ģ. ![]()
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