Fill in the blanks.
1. Carbon dioxide gas turns limewater_____.
2. Iron filings on heating with sulphur form iron___.
3. Burning of petrol is a
______change.
4._____and_____are necessary for rusting.
5. Crystals of a substance are obtained from its_____
solution.
Answers
Answer:
1. When carbon dioxide reacts with the lime water Ca(OH)2, it forms calcium carbonate CaCO3 which turns lime water milky.
2. 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 mixture of iron and sulphur powder is a chemical change.
3. Burning of liquefied petroleum gas is a chemical change because on heating it produces carbon dioxide and water. Hence, it is a chemical change. Evaporation of petrol does not involve any chemical reaction.
4. Rusting of iron takes place in the presence of moisture and air. So the presence of air and water vapour in air are two necessary conditions for rusting of iron.
5. The process of deriving large crystals of pure substances from their solutions is known as crystallisation. It is a physical change. Crystals of salt are obtained by the evaporation of sea water.
Explanation: