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: Loss of righting ability was scored at 1 , 3 , 5 min post dosing and at 5 min intervals thereafter for 20 min .
### Output Text:
Loss of righting ability was scored at 1 , 3 , 5 min post dosing and at 5 min intervals thereafter for 20 min . 