In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: A 72 - year - old woman was admitted to the hospital with " flash " pulmonary edema , preceded by chest pain , requiring intubation .
### Output Text:
A 72 - year - old woman was admitted to the hospital with " flash " pulmonary edema , preceded by chest pain , requiring intubation . 