What are the dramatic devices used in The Merchant of Venice, and how do they evoke the audience's emotions?

In Act II, scene 5, there's a classic example of dramatic irony. This is where the audience knows something that one or more of the characters in the play doesn't. Shylock has been invited to dinner by Bassanio. Before he leaves, he instructs his daughter Jessica to lock all the doors and windows. He also instructs her not to stick her head out of the window and stare at what he calls "Christian fools" with painted faces participating in the masquerade.
Just before Shylock leaves, his sneaky servant Launcelot turns to Jessica and gives her a secret message:

Mistress, look out at window, for all this.
There will come a Christian by
Will be worth a Jewess' eye.

Launcelot has already carried a secret letter from Jessica to her gentile lover, Lorenzo. And now he's giving Jessica a verbal reply to that letter; Lorenzo will come visit her this very evening while her father's out dining with Bassanio.
This is an example of dramatic irony because we the audience know what's going on, but Shylock is blissfully unaware that he's being taken for a fool. In terms of the audience's emotional response, it all rather depends on what we think about Shylock. If we don't like him, then we'll feel pleased that he's getting his comeuppance. However, if we find him a much more sympathetic character, then we'll be rightly appalled at Launcelot and Jessica's betrayal.