simplify and give reasons for 8 th class chap 4 exercise 4.1
Answers
Step-by-step explanation:
Give reasons for the following.
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods for heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Ans. (a) Aluminium is one of the least reactive metals, so it does not react with food items and does not alter the taste. Moreover, being a metal; aluminium is highly malleable and can be made into very thin foils which are perfect for wrapping food.
(b) Immersion rods for heating liquids are made up of metallic substances because metals are good conductors of heat and electricity. The immersion rod needs electric supply to get heated and in turn to heat liquids.
(c) A metal can displace a less reactive metal from its salt in an aqueous solution. But zinc is more reactive than copper. Therefore, copper cannot displace zinc from its salt solution.
Cu(s)+ ZnSO4 (aq) → No reaction
(d) Sodium and potassium are highly reactive metals. If kept in open, they readily react with oxygen in the atmosphere. The reaction is so quick and that sodium and potassium easily catch fire when exposed to air. To prevent accidental fire, they are stored in kerosene.