Upon being brought together a lump of whitephosphorus and chlorine gas react in flame.

Reaction of White Phosphorus and Chlorine

Purpose To observe a combination reaction

between two non-metals

To understand that a combination

reaction is a redox reaction

Demonstration

There was a brief induction period before the phosphorus began to burn in the chlorine

The white coating on the inside of the florence flask was the product of the reaction, solid phosphorus pentachloride

Concepts

1. Allotropes

2. Covalent Compounds

3. Combination Reactions

1. Allotropes Different forms of the same

element

Carbon• graphite• diamond

Phosphorus • white phosphorus P4

• red phosphorus

2. Covalent Compounds As opposed to ionic compounds Composed of two or more non-

metals Examples

• carbon + oxygen• phosphorus + oxygen• phosphorus + chlorine

Shared electrons between the elements are themselves what we call covalent “bonds”

CO CO2

P4O10

PCl5

3. Combination Reactions A + B C

P4(s) + Cl2(g) PCl5(s)

Oxidation Number Changes

Start Finish EffectP 0 5+ loses electrons

Cl 0 1- gains electrons

410

is oxidized

is reduced

Conclusions Two non-metals reacted to form

a covalent compound

The reaction was both

“Burning” occurred without oxygen as long as another oxidizing agent is present

a combination reactiona redox reaction

Comments Although the element phosphorus

is essential for life its elemental form is highly reactive and poisonous

White phosphorus is stored under water to prevent it from reacting with oxygen in the air

Red phosphorus is found in matches and is relatively air stable compared to white phosphorus

P4 + O2 P4O10