[robocop12]

So heres the situation. Lab called for putting t-butylchloride into 1M NaOH and water and bromophenol blue.
It turned blue to yellow in about 90s to 180s (did 3 tries, all fell in that range)

Now I used the same conc of tbutylchloride and NaOH yet I put acetone in, with some water, versus just acetone.

I know Acetone is a polar APROTIC substance, which favors Sn2..yet this is E2. This reaction ended up taking about 30s.

Why? If Im keeping all things constant what does acetone do to the reaction?

[discodermolide]

t-butyl chloride is insoluble in water, that is, when you added the NaOH solution you will get two immiscible phases. The reaction, therefore, happens at the interface of the two phases, making it slow as the OH has to get to the t-butyl chloride to cause the elimination. Adding an amount of acetone will probably cause the phases to partially mix resulting in a faster reaction. You didn't say how much acetone you used, if you used enough you may only get one phase in that case the reaction will be rapid.
So it is a solvent effect causing partial dissolution of the two immiscible layers resulting in a faster reaction.

[orgopete]

Hint, the water concentration is being varied. There is water in every trial.