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 highest BIS score corresponding to the inability to repeat words was 81 . 5 ( 95 % CI = 78 . 1 to 84 . 8 ) .
### Output Text:
The mean highest BIS score corresponding to the inability to repeat words was 81 . 5 ( 95 % CI = 78 . 1 to 84 . 8 ) . 