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: The mean BIS score corresponding to the last word recalled from prior to the initiation of the sedation was 96 . 7 ( + / - 2 . 4 ; range 84 to 98 ) .
### Output Text:
The mean BIS score corresponding to the last word recalled from prior to the initiation of the sedation was 96 . 7 ( + / - 2 . 4 ; range 84 to 98 ) . 