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Experiment: How to make acid cloud with a sprinkle of phosphorus

3,949 views · Published 22 June 2017 · 1:22 · Indexed 21 September 2026

Channel: MEL Science · 2017 · Science & Technology

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Warning! This experiment is not included in the MEL Chemistry subscription and is supposed to be conducted by a professional.
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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.

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.

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