In which of the following chemical changes, the physical state of the substance also undergoes a change? (i) Burning of magnesium ribbon (ii) Heating of iron and sulphur together (iii) Burning of carbon (iv) Electrolysis of water (v) Heating mercuric oxide (a) (i), (if), (v) (b) (i), (iii), (iv) (c) (iii), (iv), (v) (d) (ii), (iv), (v)
Answers
Answer:
1.(A) Burning of magnesium in air
When magnesium is burnt, it reacts with the oxygen present in air to form magnesium oxide.
2Mg+O
2
→2MgO
The magnesium ribbon burns with a bright white light. After it burns, it forms a white powder of magnesium oxide.
Explanation:
2.Burning of coal is a chemical change. When coal is burnt, the chief component, carbon is changed to carbon dioxide. This process cannot be reversed.
3.When iron filings and sulphur powder are mixed and heated they undergo a chemical reaction and form ferrous sulphide (FeS). It is a new substance which has properties entirely different from Fe and S. Therefore, heating of a mixture of iron and sulphur powder is a chemical change.
4.Electrolysis of water is a chemical process as it involves with the conversion of water to hydrogen and oxygen. At the same condition again you cannot change them to water. There is chemical bond breaking and formation of new bonds occur. That is why its considered as a chemical change.
5.Actually, on heating, mercuric oxide decomposes to form mercury and oxygen, i.e., two new products arc formed. The mercury vaporises and liquefies on the cooler parts of the test Heating mercuric oxide brings tube. ... Thus, strong heating of mercuric oxide is a permanent change, which cannot be reversed.
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