Question

hold one moist and one dry strip of blue litmus paper over dry HCL acid gas .which strip will turn red and why

Answer 1

It so happens because any two or more element reacts with each other only in presence of hydrogen ions . Thus a dry litmus paper will not show any effect in the presence of dry HCL due to the absence of moisture(H+ ions) in the the litmus paper , whereas on putting a drop of water,the blue litmus paper immediately turns to red due to the presence of water in it hence presence of hydrogen ions(H+ ions).

Answer 2

The moist litmus paper will turn red.

Because,

• Litmus paper turns red when it detects the H+ ion of an acidic substance.

• The gaseous HCl doesn't dissociates into H+ and Cl- ions in the normal dry conditions.

• But, when the gaseous HCl gets into the contact of the water present in the moist litmus paper,then it breaks into H+ and Cl- ions and the produced H+ ions produce the red colour of the litmus paper.