How does Douglass use irony to challenge the ideology of slavery?

Douglass uses irony in his narrative by highlighting the contradiction between the ideals of freedom and equality in America and the reality of slavery. By depicting the brutal treatment of slaves and the hypocrisy of slave owners, he challenges the notion that slavery is justified and exposes the deep-seated racism in society. This use of irony forces readers to confront the harsh truths of slavery and question the morality of the institution.