How does Shakespeare create a sense of fear and confusion in Act 5, scene 1?

Setting
Language
Structure of lines
Use of characters
Dramatic methods

• Unity of time and place by 'Outside Bianca's house' - links to beginning of play in Act 1-scene 1 where the audience were first introduced to Iago and Roderigo getting up to no good. Act 1 -scene 1, audience were aware that the characters were nasty what with trying to get Othello and Desdemona in trouble but a much darker atmosphere is set in act 5 scene 1 as it set at night time - pathetic fallacy to portray a murder?

• Iago instructs Roderigo to 'stand behind this bulk', making the audience fully aware that Roderigo is still obeying to Iago's devilish plan. This is where tension begins in the audience because they know that they're attempt to kill Cassio is coming very close.
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  Iago tells Roderigo that he'll be 'at thy elbow', this is dramatic irony as he is anything but supporting him. Further on in the scene, the audience see that Iago wants Roderigo dead as much as Cassio when he says that 'every way makes his gain'. This emphasises Iago's duplicitous characteristics once more as he presents yet another empty promise. Additionally, Shakespeare portrays Iago as the devil when he says 'I'll be at thy elbow' because this symbolises medieval myths of the devil being summoned by calling his name. Iago is referring to himself as the devil as he says he will help when called.
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  Confusion is evoked in the audience when Roderigo admits to having 'no great devotion to the deed', making the audience question why he will do it then. Shows that he is too afraid of Iago to challenge him - evoking fear once more for the antagonist. 
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  Psychopathy - makes the audience feel fear as 'every way makes his gain', when referring to the two men dying. This would scare he audience as he is so unmerciful. 
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  Perhaps Iago is afraid of himself and since his lack of morals has been made so aware by Cassio's purity, Iago's corruption that he must get rid of him, in order to make himself feel better. Relates to other parts in the play. 
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  Catharsis, as theoried by Aristotle, is put into action when they feel bad for Cassio as he is being attacked for no reason by Roderigo.
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  Confusion is aroused in audience when Othello mistakes Roderigo for being Cassio 'O Villain that I am/It is even so'. Shows that Iago is Othello's eye and ears and this is Othello's tragic flaw. This is emphasised because of the setting being at night - highlighting the mood of death.
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  Fear for desdemona when Othello realises that he has to present his end of the deal where he kills Desdemona 'thine eyes, are blotted'. Here, we see just how vicious Othello is (negro-stereotype?) and this is where the peripeita takes place rapidly. Everything is downhill from now on.
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  Confusion as to who Roderigo is calling a 'wretched villian' - himself? Cassio? or Iago?
• Bianca is confused as to why she is being blamed for the attack and states that she is as honest as Emilia - this would not be seen to be true as they are from two different realms of the patriarchal society, Emilia would be seen as the good honest woman who tends to her husbands needs whilst Bianca would be seen as a mad/bad woman as she is a prostitute. Emilia is also confused as to why Bianca would even think that those two are equal. Marxism possibly - class.
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  Iago manufactures the idea that Cassio and Roderigo are fighting over Bianca, this take the attention from Iago.