Procedure: makes sure not to cross contaminate!!!! Use the graduated cylinder to

Question

Procedure: makes sure not to cross contaminate!!!! Use the graduated cylinder to measure out 25.0 mL of the water:acetone solution and add the solution to the 125 ml Erlenmeyer flask. Place the magnetic stir bar in the in the 125 ml Erlenmeyer flask, place the flask on the stir plate and stir at a medium rate. Add 2 drops of bromothymol blue to the flask. Use the 1 ml calibrated pipette to measure and add 1.00 ml of 0.100 M NaOH to the flask. Be sure that none of the NaOH solution ends up stuck to the side of the flask. bullet Why is it important to ensure to that the NaOH don't stick to the sides of the flask? Use the 2 ml calibrated pipette to measure 2.00 ml of 0.100 M tert-butyl chloride in acetone. Add the 2.00 ml of tert-butyl chloride solution to the flask(be careful none sticks to the sides) while your partner simultaneously starts the stopwatch. The passage of one half-life will be indicated by a color change from blue to yellow. The record elapsed time in seconds upon color change as precisely as possible. Repeat (l)-(6). Prelab Questions: Adding 3 elementary steps given in introduction, write the overall (sum) equation. If the solution takes 55 seconds to change color, calculate the rate constant. Write a rate expression for this reaction with all values known filled in. What order reaction is this and how did you know? Is the rate constant (k) constant under all conditions?

Explanation / Answer

1. Overall reaction : t-Butyl chloride + NaOH ==> t-Butyl hydroxide + Cl-

2. t1/2 = 0.693/k

or k = 0.693/t1/2 = 0.693/55 = 0.0126 /sec

3. molarity of t-butylchloride in the flask = 2mL*0.1M/(25+2)mL =0.0074M

rate = k[t-butyl chloride]

rate = 0.0126 /sec[0.0074]

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4.This is an example of SN1 reaction which is Nucleophilic substitution via unimolecular reaction. So, this is a first order reaction.

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