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: Valproate - induced hyperammonemic encephalopathy is an uncommon but serious effect of valproate treatment .
### Output Text:
<span class="chemical">Valproate</span> - induced hyperammonemic encephalopathy is an uncommon but serious effect of <span class="chemical">valproate</span> treatment . 