Question

i. Name a metal for each case :

(a) It does not react with cold as well as hot water but reacts with steam.

(b) It does not react with any physical state of water.

ii. When calcium metal is added to water the gas evolved does not catch fire but the same gas evolved on adding sodium metal to water catches fire. Why is it so ?​

Answer 1

a. aluminium , zinc , magnesium

b. mercury, gold , silver

c. In explanation

A. Magnesium has almost no reaction with cold water. It reacts very slowly with hot water. It reacts with steam when being heated and gives hydrogen gas and metal oxide

B. The physical state of the water that is present naturally is in form of solid, liquid and the gas.

The gaseous form is present after 100℃ and the liquid form is present after 0℃ to 99.999℃ and below zero it is solid ice.

The metal that doesn’t react well with the physical states of water are gold, silver, mercury, lead, etc.

The previous mentioned metal doesn’t react with water but some alkali metals like sodium and potassium react vigorously with water.

Therefore, metals like sodium and potassium is kept in kerosene or other inert liquid

C. When calcium metal is added to water and when sodium metal is added to water in both of the cases hydrogen gas is evolved but the difference is that when the calcium metal is added to water there is not much gas involved or released which is insufficient for hydrogen to catch fire or to burn.

Answer 2

Answer :

i.

• a. Iron. Metals like iron does not react with water because they are less reactive metals and can only react with steam and moist air.
• b. Copper. Copper is one of the least reactive metals in the reactivity series and hence, does not react with water in any of the conditions.

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ii.

• The reaction of calcium and water is less violent than that of with sodium. The heat evolved during the reaction is not sufficient for the evolved hydrogen to catch fire. Also, calcium sinks in water and the hydrogen evolved as bubbles stick to the surface of calcium metal and makes it to float on water.

• On the other hand, in the case of sodium, the reaction is very violent. Sodium metals is less denser than water and it floats on the surface. The heat produced in the reaction is sufficient to ignite the evolved hydrogen and it immediately catches fire.