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: In particular , the tendency of cocaine to produce chest pain ought to be in the mind of the emergency nurse when faced with a young victim of chest pain who is otherwise at low risk .
### Output Text:
In particular , the tendency of <span class="chemical">cocaine</span> to produce chest pain ought to be in the mind of the emergency nurse when faced with a young victim of chest pain who is otherwise at low risk . 