"Acid Cloud" experiment

How to obtain phosphoric acid using red phosphorus

In this stun­ning ex­per­i­ment, there’ll be a lot of smoke, a mys­te­ri­ous dis­ap­pear­ance, and a so­lu­tion will change col­or.

Reagents and equip­ment:

  • red phos­pho­rus;
  • a 2-l flask;
  • spir­it burn­er;
  • lit­mus so­lu­tion;
  • dis­tilled wa­ter;
  • spoon for burn­ing;
  • cork.

Step-by-step in­struc­tions

Pour dis­tilled wa­ter into a 2-l flask and add the lit­mus so­lu­tion. In the spoon for burn­ing light the red phos­pho­rus in the spir­it burn­er flame and low­er into the flask. Seal with a cork. The col­or of the lit­mus changes to red, and the white smoke grad­u­al­ly dis­ap­pears.

Pro­cess­es de­scrip­tion

When the phos­pho­rus burns, phos­pho­rus(V) ox­ide forms.

Pred + О₂ → Р₂О₅

As phos­pho­rus(V) ox­ide is an acidic ox­ide, when it in­ter­acts with wa­ter, phos­phor­ic acid forms.

Р₂О₅ + 3Н₂О →2Н₃РО₄

Lit­mus is an acid-base in­di­ca­tor, and de­pend­ing on the pH of the medi­um has three col­ors: red (an acid medi­um), pur­ple (a neu­tral medi­um), and blue (an al­ka­line medi­um).

Phos­phor­ic acid changes the col­or of the lit­mus in­di­ca­tor from pur­ple to red.

Safe­ty pre­cau­tions

Work in pro­tec­tive gloves and glass­es and in a well-ven­ti­lat­ed room. Ob­serve safe­ty rules with com­bustible sub­stances.

Warn­ing! Sub­stances of this ex­per­i­ment are tox­ic and high­ly dan­ger­ous for your health. Do not try this at home. Only un­der pro­fes­sion­al su­per­vi­sion.

Try it