“Breath as a reagent” experiment

How to change a color of a solution just by a breath

Chemists are real ma­gi­cians, only they have sci­ence on their side! They can show an in­ter­est­ing and spec­tac­u­lar ex­per­i­ment with a few reagents.

Safe­ty pre­cau­tions

This ex­per­i­ment is safe. Care must be ob­served in work­ing with phe­nolph­thalein, it is a lax­a­tive. If the so­lu­tion gets into the mouth, it must be rinsed out with wa­ter.

Reagents and equip­ment:

  • cal­ci­um ox­ide (1 g);
  • dis­tilled wa­ter (300 ml);
  • flask;
  • 1% phe­nolph­thalein so­lu­tion;
  • straw;
  • beaker.

Step-by-step in­struc­tions

We dis­solve cal­ci­um ox­ide in 300 ml of wa­ter. A di­lut­ed so­lu­tion of cal­ci­um hy­drox­ide is the re­sult. Then we pour the so­lu­tion into a flask and add a few drops of in­di­ca­tor, for ex­am­ple phe­nolph­thalein. We put a straw in it and pass ex­haled air through the so­lu­tion. We ob­serve the change in the col­or of the so­lu­tion and the pre­cip­i­ta­tion of a white sed­i­ment.

Pro­cess­es de­scrip­tion

Cal­ci­um ox­ide eas­i­ly dis­solves in wa­ter with the for­ma­tion of cal­ci­um hy­drox­ide. The so­lu­tion has an al­ka­line medi­um, as when the phe­nolph­thalein in­di­ca­tor is added, the col­or changes to ma­gen­ta. When the so­lu­tion has ex­haled air passed through it, which con­tains more car­bon diox­ide than the at­mo­spher­ic air, the white sed­i­ment of cal­ci­um car­bon­ate starts to pre­cip­i­tate, and the so­lu­tion be­comes col­or­less, as the medi­um be­comes neu­tral, as cal­ci­um hy­drox­ide turns into an in­sol­u­ble car­bon­ate.