Q.3 Give reasons why the following are considered as chemical changes.
1. Copper carbonate on heat gives copper oxide and carbon dioxide.
2. A bright light is seen evolved when a strip of magnesium is heated.
3. Sulphur when burnt in air evolves a gaseous acidic product.
4. An iron nail kept open in the atmosphere rusts.
5. A piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid.
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Answers
Answer:
Q3) Give reasons why the following are considered as chemical changes.
1) Copper Carbonate on heat gives copper oxide and carbon dioxide.
2) A bright light is seen to have evolved when a strip of magnesium is heated.
3) ulphur, when burnt in air, evolves a gaseous acidic product.
4) An iron nail kept open in the atmosphere rusts.
5) A piece of magnesium strip is dropped into a beaker containing dilute hydrochloric acid.
Solution:
Copper carbonate is green colored which gives copper oxide and carbon dioxide, which are new substances with new properties. This reaction is irreversible, hence it’s a chemical change.
CuCO3-->CuO+CuO2
When magnesium strip is heated it produces magnesium oxide in air. The composition changes to white powder and the change is irreversible. Hence, it is a chemical change.
Sulphur produces sulphur gas when burnt in air, this acidic product is new and changes the composition of sulphur. Hence, it is a chemical change.
Iron rust is a brown flaky powder formed after iron reacts with air, a new product with new properties is formed which are different from iron metal. Hence, it's a chemical change.
4Fe+3O2-->2Fe203 H2O
When a piece of magnesium strip is dropped in dilute hydrochloric acid, a new product hydrogen gas is evolved and Magnesium chloride has properties different from that of magnesium, which is irreversible and hence, it’s a chemical change.
Answer:
Q.3 Give reasons why the following are considered chemical changes.
1. copper carbonate [CuCO3] green color on heating gives copper oxide [Black color CuO] and CO2. Hence composition is changed new substances CuO [Black] and CO2 with new properties are produced and it is an irreversible reaction hence it is a chemical change.
2. A bright light is seen evolved when a strip of magnesium is heated. Answer: Magnesium is heated producing a bright light to form MgO in the air is a chemical change as the composition changes (MgO white powder) is formed, is irreversible. Sulphur when burnt in the air evolves into a gaseous acidic product.
3. When the magnesium strip is heated it produces magnesium oxide in the air. The composition changes to white powder and the change is irreversible. Sulphur produces sulphur gas when burnt in the air, this acidic product is new and changes the composition of sulphur. Hence, it is a chemical change.
4. Rusting is a chemical reaction that takes place when the iron is exposed to moist air. It reacts with oxygen and water to form iron oxide. So, the iron nail kept near the gateway of India in Mumbai will rust faster because there the humidity is more.
5. When a piece of magnesium strip is dropped in dilute hydrochloric acid, a new product hydrogen gas is evolved and Magnesium chloride has properties different from that of magnesium, which is irreversible and hence, it's a chemical change.