Writing with White Phosphorus
A solution of white phosphorus in carbon disulfide is placed on a piece of filter paper. Shortly thereafter, the paper catches fire in the places where the solution was applied. The phosphorus combines with oxygen to form P4O10 in a highly exothermic reaction. The equation for the reaction is given.
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Keywords
combustion reaction, descriptive chemistry, elements, exothermic process, oxygen, phosphorus/phosphorus oxides/phosphoric acid, reactivity - kinetic/thermodynamic stability, redox reaction, spontaneous process
Multimedia
Writing P4
Play movie
(QuickTime 3.0 Sorenson, duration 43 seconds, size 3 MB)
White phosphorus dissolved in carbon disulfide is taken into a medicine dropper and used to write on a piece of filter paper. The pale yellow color of the white phosphorus can be clearly seen on the paper as the writing is done. As the solvent carbon disulfide evaporates away, the phosphorus begins to react with oxygen from the air. This spontaneous combustion reaction is an exothermic one that causes the paper to char, leaving P4, the formula for white phosphorus burned into the piece of filter paper.
 White phosphorus dissolved in carbon disulfide is used to write. |
 The phosphorus reacts with oxygen. |
 The formula for white phosphorus is burned into the paper. |
Additional still images for this movie
Writing X
Play movie
(QuickTime 3.0 Sorenson, duration 35 seconds, size 2.4 MB)
An element dissolved in carbon disulfide is taken into a medicine dropper and used to write on a piece of filter paper. As the solvent, carbon disulfide, evaporates away, the element begins to react with oxygen from the air in a spontaneous, exothermic combustion reaction. What is this element?
 White phosphorus dissolved in carbon disulfide is used to write. |
 The phosphorus reacts with oxygen. |
 The letter 'X' is burned into the paper. |
Additional still images for this movie
Discussion
The white allotrope of phosphorus consists of tetrahedral P4 molecules. When exposed to air in the dark it glows with greenish light, a phenomenon known as phosphorescence. In moist air, white phosphorus ignites spontaneously at 30 oC. The ignition temperature is higher in dry air. White phosphorus is extremely dangerous and toxic-much more so than the black and red allotropes.The equation for the reaction seen here is
P4 + 5O2 --> P4O10
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Demonstration Notes, Warnings, Safety Information, etc.
Exam and Quiz Questions
P4 segment
1. What element is the phosphorus reacting with?
2. Is the phosphorus very reactive? Use evidence from the video to support your answer.
3. List as many observations as possible concerning this video segment.
X segment
1. List as many observations as possible concerning this video segment.
2. Turn on the voice-over track for this question!
What element is dissolved in the carbon disulfide?