[Fischer]

So we carried out an experiment; t-butyl chloride in the presence of NaOH and water. Now the first reaction was using 0.1 M t-BuCl, and 0.2 mL of 0.1 M NaOH and 7.8 mL H2O.

The time of the reaction was relatively fast (about 65s)

Now the next reaction was carried using 5.7 mL H2O, 0.5 mL NaOH and 4.2 mL t-butyl chloride.
The time of the reaction increased to about 185s.

I don't know how to approach this. I know it's a SN2 reaction (even though it's t-BuCl, it still went through Sn2), I know that a polar protic solvent would increase the reaction time, so increasing water would increase the reaction time, however here, we decreased the amounts of water and increased the amounts of both substrate and NaOH.

Can someone please explain this? I'm I on the right track?

[Dan]

What is the overall concentration of the reagents at the beginning of each experiment? You have said that you used 0.1 M t-BuCl in the first experiment, but have not told us how much.

How do you know this is an S_N2 reaction?

[orgopete]

If I understand this correctly, you increased the NaOH and t-BuCl concentrations and the reaction became slower. Normally, if you doubled the NaOH or t-BuCl concentration, the rate should double and if both should 4x if SN2. If you think of the first conditions as modifications of the second, then adding water or reducing the NaOH and t-BuCl concentrations has increased the rate. What should that indicate about the mechanism?

[TwistedConf]

I know it's a SN2 reaction (even though it's t-BuCl, it still went through Sn2)

I'm quite willing to bet that it didn't.