Is it copper sulfate or sulphate?

Both "copper sulfate" and "copper sulphate" are correct; the choice depends on regional English conventions.

This spelling variation exists across all sulfate/sulphate compounds. United States and Canada use "sulfate," while United Kingdom, India, Australia, and many Commonwealth countries use "sulphate." Scientific journals typically accept both, though they may have style preferences. When writing, maintain consistency throughout your document.